An Illustrated and Cross-Referenced Glossary of
Malacological and Conchological Terms

by Paul S. Mikkelsen

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All Terms in the Glossary
1754 terms were found.

Term Definition

MARGIN   [need definition].

PRODISSOCONCH   [need definition].

ABALONE   A member of the gastropod family Haliotidae (e.g., Haliotis spp.). The interior of Abalone shells exhibit a NACREOUS layer known as MOTHER OF PEARL.

ABAPICAL   Away from the APEX; opposite of ADAPICAL; see also: APICAL.

ABAXIAL   Away from the AXIS; opposite of ADAXIAL; see also: AXIAL.

ABERRANT   Abnormal; of freak shape or coloration.

ABORAL   Situated away from the mouth; see also: ORAL.

ABUTTING   Touching; contiguous; adjacent; see also: NAUTILOCONIC.

  Ocean depths from 2,000 to 6,000 meters, See also: HADAL, PELAGIC.

ABYSSOPELAGIC   The PELAGIC depth zone 4,000 to 6,000 meters. See also: PELAGIC; EPIPELAGIC (0-200m depth); MESOPELAGIC (200-1000m depth); BATHYPELAGIC (1000-4000m depth; HADAL (greater than 6,000m depth); NERITIC; OCEANIC; BENTHIC; PLANKTONIC.

(= ABO; A.B.O.)
  [need definition]. Term coined by Mel Carriker.

ACCESSORY MUSCLE   Any muscle other than ADDUCTOR and PALLIAL muscles, with SCAR of attachment to shell (convenient noncommittal term when referring to scars of muscles of uncertain origin).

ACCESSORY PLATE   A secondary CALCAREOUS structure formed in some bivalves (e.g., the Pholadidae) to protect the soft parts; see also: HYPOPLAX; MESOPLAX; METAPLAX; PROTOPLAX; SIPHONOPLAX.


ACETABULUM   The cup-shaped portion of a SUCKER of a CEPHALOPOD arm or TENTACLE.


ACLINE   Perpendicular to HINGE AXIS or almost so (applied to HINGE TEETH or, in some genera, to direction of elongation of body of shell; = ORTHOCLINE.

ACTINODONT   Descriptive of a bivalve shell having a HINGE with teeth that radiate outward from the UMBOS; with teeth radiating from BEAK, outer ones more or less elongate (applied to certain bivalves of early origin).

ACULEATE   Having sharp SPINES; see also: SPINOUS.

ACUMINATE   Tapering to a slender point; see also: ATTENUATED.

ACUTE   Sharply angled, pointed or edged; e.g., a spire with an angle of less than 90 degrees.

ADAPICAL   Toward the APEX; opposite of ABAPICAL; see also: APICAL.

ADAXIAL   Toward the AXIS; opposite of ABAXIAL; see also: AXIAL.

ADDUCTOR MUSCLE   One of two muscles connecting bivalve shells, tending to draw them together; these muscles leave diagnostic impressions on the inner surface of the valves; see also: ADDUCTOR SCAR; DIMYARIAN; MONOMYARIAN.



ADNATE   Barely attached. A term sometimes applied to shells of the bivalve family Unionidae, which are joined together by rigid CALCAREOUS material rather than a flexible LIGAMENT.


ADULT   Fully grown; sexually mature; see also: JUVENILE.

ADULT WHORLS   All whorls of a GASTROPOD shell beyond those of the nucleus, or PROTOCONCH; = TELEOCONCH; see also: NUCLEAR WHORL; PROTOCONCH.

AESTHETES   Sensory epidermal PAPILLAE in the Gastropoda and Polyplacophora; small ones are called MICRAESTHETES, while larger ones are MEGALAESTHETES, and may form eyes with a simple lens.

  To pass the summer or dry periods in an inactive state (common for some land snails, which may create an EPIPHRAGM to seal the APERTURE of the shell to conserve moisture); see also: HIBERNATE.

AFF. (AFFINIS)   An indication that a species has an affinity to another species, but is not that species; e.g. Conus aff. crocatus Lamarck, 1810. See also: CF (CONFER).

ALATE   Winged; having alae; = AURICLE; see also: BIALATE; DIFFUSE; DILATED; PINNATE.

ALBINISTIC   Tending toward being an ALBINO; nearly all white; see also: MELANISTIC.

ALBINO   All white in shell and soft parts; often, without having seen the ANIMAL, the white shell is called an albino; see also: ALBINISTIC.

ALIVINCULAR   Type of bivalve LIGAMENT not elongated in longitudinal direction nor necessarily situated entirely posterior to beaks, but located between CARDINAL AREAS (where present) of respective valves, with lamellar layer both anterior and posterior to fibrous layer; example: Ostrea; see also: DUPLIVINCULAR; MULTIVINCULAR; PARIVINCULAR.

ALLOMORPHISM   A term used erroneously by some authors for XENOMORPHISM.

AMBISEXUAL   Producing both eggs and sperm side by side; see also: HERMAPHRODITE; MONECIOUS.

AMMONITE   Members of an extinct group of CEPHALOPODS in the subclass Ammonoidea. See also: BELEMNITE.

AMMONOTELIC   [need definition]; see also: URICOTELIC.


AMPHIDETIC   Extending on both anterior and posterior sides of the BEAK; said of the ligamentary area in certain bivalve shells, e.g., Arca.

ANACHOMATA   Small tubercles or ridgelets on periphery of inner surface of right valve of bivalves; see also: CATACHOMATA; CHOMATA (sing. CHOMA).

ANAL   Pertaining to or near the anus or posterior opening of the alimentary canal.

ANAL CANAL   = POSTERIOR CANAL; = ANAL SULCUS. See illustration: Composite Gastropod.

ANAL FASCIOLE   A band on the outer lip generated by a sinus, notch, or slit, close to the suture and anal opening of a gastropod aperture; see also: SELENIZONE; SLIT BAND.

ANAL NOTCH   A break in the circumference of the aperature over the spot where the outgoing current leaves the mantle cavity on the right; i.e., a notch in the outer lip where it joins the body whorl (present in mesogastropods, especially in the Turridae [the "TURRID NOTCH"]). See illustration: Composite Gastropod.

ANAL SINUS   [need definition]. See illustration: Composite Gastropod.

ANAL SIPHON   A tube exiting at the posterior end of the gastropod aperture, through which solid waste matter is voided; in the Typhinae (Muricidae), the anal siphon is housed in a shelly tube.

ANAL SULCUS   A groove in the posterior portion of the aperture that accommodates the ANAL SIPHON; = POSTERIOR CANAL; = ANAL CANAL.

ANASPID   A Opisthobranch gastropod which belongs to the suborder Anaspidea, which is an older name for the Aplysiomorpha (SEA HARES, e.g. Aplysia spp.); the term is from the Greek meaning "without a shield" and refers to the lack of a head shield such as is common to the CEPHALASPID gastropods.

ANGULATE   Tabulate, as distinct from CONVEX; said of the whorl profile; formed with corners; angled. See also: BIANGULATE.

ANGULATION   The edge along which two surfaces meet at an angle.

ANIMAL   The fleshy, or soft part of a MOLLUSC; see also: CONCH.

ANISOMYARIAN   The condition, in bivalve molluscs, of having adductor muscle scars of unequal size, with the posterior one usually being the larger of the two; see also: MONOMYARIAN; DIMYARIAN; HETEROMYARIAN.

ANNULATE   Bearing more or less concentric rings, as on the inner surface of a gastropod operculum; see: OPERCULUM, ANNULATE.

ANNULUS   One of several concentric rings.

ANODONT   Lacking hinge teeth (in bivalves); = EDENTULOUS.


ANTERIOR   Toward the end at or from which the head, in gastropods, or the FOOT in bivalves, tends to emerge; opposite of POSTERIOR; see also: PROSOGYRATE.

ANTERIOR CANAL   The SIPHONAL CANAL; a tubular or trough-like extension of the anterior end of the gastropod aperture, enclosing the INHALANT SIPHON; = CAUDAL CANAL; see also: POSTERIOR CANAL.

ANTERODORSAL   Being both forward and upward; toward the front and upper regions.

ANTEROLATERAL   Forward, towards the ANTERIOR and also toward the side or LATERAL.

ANTEROVENTRAL   Being both forward and downward; toward the front and lower regions; see also: POSTEROVENTRAL.

ANTEROVENTRAL MARGIN   In bivalves, the anterior end of the valve margin opposite the hinge; See also: POSTEROVENTRAL MARGIN;

APERTURAL   Pertaining to the APERTURE.

APERTURAL LIP   The most recently formed margin of the aperture; = PERISTOME; see also: HOLOSTOMATE; SIPHONOSTOMATE; see also: INNER APERTURAL LIP; OUTER APERTURAL LIP.

APERTURAL LIP, INNER   [need definition]. See illustration: Composite Gastropod. See also: APERTURAL LIP; OUTER APERTURAL LIP

APERTURAL LIP, OUTER   [need definition]. See illustration: Composite Gastropod. See also: APERTURAL LIP; INNER APERTURAL LIP.

APERTURAL TOOTH   Shelly protuberances in the APERTURE or opening in the shell of a gastropod.

APERTURE   The major opening of a GASTROPOD shell, through which the animal protrudes. See illustration: Composite Gastropod. See also: PERISTOME; HOLOSTOMATE; MOUTH; SIPHONOSTOMATE.

(pl. APICES)
  The first-formed end of a gastropod shell, generally more or less pointed; the tip of the PROTOCONCH or NUCLEAR WHORLS; opposite of BASE; see also: APICAL.

APICAL   Pertaining to the APEX; see also: ABAPICAL; ADAPICAL.

APICAL PLUG   A CALCAREOUS plate at the spire-end of the tubular shells of the Caecidae (Gastropoda); see also: MUCRO.

APLACOPHORAN   A member of the class Aplacophora, a group of molluscs made up of the subclasses Neomeniomorpha (=Solenogastres) and Chaetodermomorpha (=Caudofoveata). See the WHOI website for details.

APOMORPHY   A derived or specialized character. See also: PLESIOMORPHY; SYNAPOMORPHY.>.

See the Paleos website for greater detail.

  In bivalves: A projecting peg-like or finger-like structure, functioning as a support for a muscle, e.g., that serving for attachment of pedal muscle in the Pholadidae or adductor muscle in some RUDISTS; = MYOPHORE. See also: APOPHYSIS (2).

  In CHITONS, the articulating plate on valves II to VII of a chiton shell. See also: APOPHYSIS (1).

APPRESSED   Pressed against or lying flat against another surface; having the WHORLS overlapping; see also: ADHERENT.

AQUACULTURE   The farming of organisms or plants in a water (AQUATIC) environment. The term is often used in reference to both freshwater and marine environments, but MARICULTURE is a better term for referring to marine environments.

AQUATIC   Pertaining to or living in the water; sometimes restrictively used to refer to fresh water only (as opposed to OCEANIC; MARINE); see also: FLUVIATILE; FRESH WATER; ESTUARINE; FLUVIATILE.

ARAGONITE   One crystalline form of CALCIUM CARBONATE, CaCO3 most evident in mollusks as NACRE or MOTHER OF PEARL; see also: CALCITE; VATERITE.

ARBOREAL   Pertaining to or living entirely in the trees; see also: TERRESTRIAL; HABITAT.

ARCHEOGASTROPOD   A large group of marine prosobranch gastropods, comprising the taxonomic order Archeogastropoda, which initially thrived in the Cambrian and which are still well represented today. They are mainly HERBIVOROUS, typically having two GILLS and a double-chambered HEART. To reproduce, their EGGS and SPERM are released into the water.

ARCHIBENTHIC   Ocean bottom depths from 800 to 1,000 meters; See also: BENTHIC; HADAL


ARGONAUT   The common name for Argonauta argo (and others of that genus), a CEPHALOPOD mollusc that lives a PELAGIC existence in the tropics and subtropics. The female produces an egg case called the PAPER NAUTILUS.

See: Mangold (1922-2003), Katharina M., Michael Vecchione, and Richard E. Young. 2010. Argonautidae Tryon, 1879. Argonauta Linnaeus 1758. Paper Nautilus. Version 03 February 2010.

Photo: Argonauta argo Linne, 1758

ARK SHELL   A member of the BIVALVE family Arcidae.
See the website: iEspana for examples of Arc Shells.

ARM   In squid, all but the 4th pair (TENTACLES) of 5 pair of appendages surrounding the mouth.

ARROW-HEADS   A common name by which fossils of the genus Belennites are known.

ARTICOID TYPE   Type of HETERODONT dentition in bivalves, intermediate between LUCINOID and CORBICULOID types; formerly termed: CYPRINOID TYPE.

ARTICULAMENTUM   Inner layer of a CHITON shell; the inner, usually hard, semi-porcelaneous shell layer, generally projecting past the TEGMENTUM on the sides and front of the valves to form the INSERTION PLATES and the sutural laminae.

ARTICULATED   Jointed; applied to parts of a shell which are fitted or jointed into each other (e.g., the valves of CHITONS, the OPERCULUM and shell of NERITES).

ASCOGLOSSAN   [need definition]. Newer, preferred term for the old term: Sacoglossan. They have a UNISERIATE RADULA from which old teeth fall from the RADULA RIBBON into an ASCUS SAC. See also: SEA SLUG; NUDIBRANCH.
Photo: Elysia chlorotica (Gould, 1870)

ASCUS SAC   The pouch-like container in ASCOGLOSSANS (previously called Sacoglossans) which stores old, used RADULA TEETH.

ASPELLOID   An informal group within the family Muricidae, which contains the genera Aspella, Dermomurex, and Ingensia.

ASTHENODONT   Hinge often essentially mactrid, but usually degenerate or OBSOLETE, owing to modifications due to the burrowing habit.

ATTACHED   Refers to shell which are connected to the substrate in some way, perhaps by a byssus (e.g., Mytilus spp.) or by calcareous secretions (e.g., Chama spp. or Spondylus spp.); see: FREE; ATTACHED BIVALVE; RADICATED; REPENT; VALVE, INFERIOR; VALVE, LOWER; ADHERENT; REPENT; PLEUROTHETIC.

ATTENUATED   Becoming thin and fine; see: ACUMINATE; LIGULATE.

  "Of authors;" when several authors erroneously identify and publish a name that does not apply to the original description, it is referred to (for example) as Conus crocatus of authors, OR: Conus crocatus Auctt. It means this cone is not true Conus crocatus Lamarck, 1810, but rather what authors have thought was crocatus; see also: TESTE.

AUGER   Common name for a SNAIL in the family Terebridae.

AURICLE   An anterior or posterior projection along the hinge line of a bivalve shell, commonly separated from body of shell by a notch or sinus; = HINGE EAR. See illustration: Composite Bivalve. See also: ALATE; BIALATE; SUBMARGIN.

(sing. CRUS)
  Blunt internal ridges, swelling out distally as low tubercles, marking lower border of auricles in some Pectinidae.

AURICULAR SULCUS   External furrow at junction of AURICLE (of bivalves) with body of shell. See illustration: Composite Bivalve.

AURICULATE   Having ears or ear-like appendages, e.g., the shells of the Pectinidae, or some ascoglossan rhinophores (Stiliger spp.); those shells having but one ear are UNIAURICULATE, while those with two ears are BIAURICULATE; see also: BIALATE.

AURIFORM   Shaped like a human ear; used in describing the rhinophores of Hermaea spp.; see also: AURICULATE; HALIOTOID.

AUSTRAL   Pertaining to the south (i.e., southern hemisphere); southern.

AUTOPHAGY   Eating part of itself.

AUTOTOMY   Voluntary separation of a part of the body; self amputation (usually initiated to avoid predation).

AVICULIFORM   [need definition].

AXIAL   Pertaining to or more or less parallel to the axis of coiling in a gastropod shell; see also: ABAXIAL; ADAXIAL; SPIRAL.

AXIAL SCULPTURE   SCULPTURE running parallel to the axis of the gastropod shell; see also: CONCENTRIC SCULPTURE.

AXIS   The center around which the WHORL of a gastropod shell coil. See illustration: Composite Gastropod. See also: COLUMELLA.

BANDING   A color marking in continuous stripes; see also: FASCIATE.
Photo: Melampus coffeus (Linne, 1758)

BASAL   Pertaining to the base or bottom.

BASAL FASCIOLE   A special band on the base of a shell formed by a series of more or less curved growth lines that define the SIPHONAL SINUS (canal).

BASAL FOLD   A fold (PLICA) near the anterior end of the columella and above the SIPHONAL CANAL; see also: COLUMELLAR FOLD.

BASAL MARGIN   Edge of shell opposite hinge, in bivalves; = VENTRAL MARGIN.

BASAL TOOTH   Calcareous deposit on the base of the apertural lip.

BASE   In coiled gastropods, the area below the periphery of the body whorl, excluding the aperture; opposite of APEX; in uncoiled or limpet-like gastropods, the apertural rim; also used, less precisely, for the flattened apertural side of cowries (Cypraeidae). In bivalves, the basal margin opposite the upper or hinge margin.

BATHYAL or BATHYPELAGIC   The PELAGIC depth zone 1,000 to 4,000 meters. See also: PELAGIC; EPIPELAGIC (0-200m depth); MESOPELAGIC (200-1000m depth); ABYSSOPELAGIC (4000-6000m depth; HADAL (greater than 6,000m depth); NERITIC; OCEANIC; BENTHIC; PLANKTONIC.

BEACHWORN   Referring to the quality of a shell as being of poor color and texture due to having been ERODED, as an empty dead shell, occurring on and being deteriorated by beach conditions.

BEADED   Sculptured in such a way as to resemble beads or strings of beads. See illustration: Composite Gastropod. See also: MONILIFORM.
Photo by Marlo F. Krisberg; Cerithium lutosum Menke, 1828.

BEAK (1)   In bivalves, the earliest part formed, = UMBO; any part which is drawn out like a beak or ROSTRATED. See illustration: Composite Bivalve.

See: Bivalve terminology, Anatomy of bivalves by Marlo Krisberg.

BEAK (2)   In cephalopods, the CHITINOUS plates of the mouth, which resemble the beak of a parrot.

See the excellent "Cephalopod Glossary" by Richard E. Young, Michael Vecchione, and Katharina M. Mangold.

BEAN COWRIE   Common name for Trivia spp.

BELEMNITE   Members of an extinct group of CEPHALOPODS in the subclass Belemnoidea. See also: AMMONITE.

BELOPTERA   The bony support of a species of CUTTLEFISH, partly resembling Sepia; see also: CUTTLEBONE


BENTHIC   Living on the bottom or in the bottom sediments; see also: BATHYAL; ARCHIBENTHIC, PELAGIC; PLANKTONIC.


BIALATE   With 2 wings or AURICLES, in bivalves (e.g., Pectinidae); see also: BIAURICULATE.

BIANGULATE   Having two angles. See also: ANGULATE.


BICOLORED   Composed of two different colors; see also: MULTICOLORED; VARIEGATED.

BICONIC   Composed of two conical shapes, base to base; diamond-shaped and having the spire about the same size and shape as the body whorl, in gastropods; CONICAL. See other gastropod shapes.

BIFID   Divided into two parts, often by a GROOVE; applied especially to the hinge teeth in bivalves; see also: BIFURCATE; BISECTED.

BIFURCATE   Forked, or double pronged; divided into two parts by a groove or cleft; = BIFID; BISECTED.


  The use of BINOMEN, that is a GENUS and SPECIES name combination to name and refer to a SPECIES; see also: ICZN; NONBINOMIAL.

  The combination of a GENUS and SPECIES name, conforming to the principles of binary nomenclature; the full generic and specific name of a species, e.g., Strombus gigas. Together, these names comprise the SCIENTIFIC NAME of a species; see also: COMMON NAME.

BIPARTITE   Divided into two parts; see also: TRIPARTITE.

BIPECTINATE   Having two comb-like margins; branched like a feather; see also: PECTINATE; MONOPECTINATE.

  Having two projecting parts or branches. See also: Having projecting parts or branches. See also: RAMOSE; TRIRAMOSE.


BISECTED   Divided into two parts; see also: BIFID; BIFURCATE.

BITTERSWEET   A COMMON NAME referring to a member of the bivalve genus Glycymeris.

BIVALVE   Typically, a mollusc in the class Bivalvia, with two shelly valves, such as an oyster or scallop; = CLAM. Additionally, other bivalved molluscs exist such as the Paleozoic ROSTROCONCHS, and the Recent bivalved gastropods of the family Juliidae; other phyla, such as the Brachiopoda, are not strictly referred to as "bivalves"; see: LAMELLIBRANCH; see also: UNIVALVE; MUSSEL.

BIVALVE, ATTACHED   Bivalves which have cemented themselves to a substrate, e.g., species in genera such as Crassostrea, Ostrea, Spondylus, Chama, Mytilus; see also: ATTACHED; BORING BIVALVES; CEMENTATION; INFERIOR VALVE.

BIVALVE, BORING   Bivalves with dissolve their substrate (rock or wood), forming burrows into which they exist and grow, e.g. SHIPWORMS, Teredo spp.; see also: ATTACHED BIVALVE.

BIVALVE, BROODING   A bivalve which undergoes internal fertilization, and sheds its young as miniature adults (commonly) or sometimes as larvae (less commonly) after having brooded or incubated them within the MANTLE CAVITY of the parent, e.g. Bornia spp., Parastarte spp., Lyonsia spp.

BIVALVED GASTROPOD   A GASTROPOD (e.g., Julia spp. [Ascoglossa: Juliidae]) with two VALVES, like a clam.

BLADE   An erect, flattened sculptural element perpendicular (or nearly so) to the shell surface; the broadened, distal portion of a PALLET.

BLUE MUSSEL   BIVALVES of the species Mytilus edulis or Mytilus trossulus. See also: MUSSEL.

BOARS TUSK   Common name applied to SCAPHOPOD shells of the genus Dentalium, due to their similar appearance to a boars tusk; = ELEPHANTS TUSK or, generally, TUSK SHELL.

BODY   In a gastropod shell, the body whorl exclusive of the shoulder and the siphonal canal. In bivalves, the entire shell, with the exception of WINGS or AURICLES; = DISK. In all molluscs, the ANIMAL, or soft tissue.

BODY WHORL   The most recently formed WHORL of a gastropod shell, usually enclosing most of the animal's body.
See illustration of Composite Gastropod.

BOREAL   Pertaining to the north (i.e., northern hemisphere; northern). See also: BOREAL PROVINCE; CIRCUMBOREAL.

BORER   A general term applied to species of molluscs which bore into rocks (some Pholadidae) or wood (Teredo spp.); = TEREBRATING SHELLS.

BOURRELET   Either of two portions of bivalve ligamental area flanking RESILIFER on its anterior and posterior sides, each comprises growth track and seat of the lamellar LIGAMENT. The posterior bourrelet is flattish in all oysters except the Exogyrinae, in which it is a narrow, sharp-crested spiral ridge on the left valve and a corresponding GROOVE on the RIGHT VALVE.

  The gills; see: GILL for list of the various type of taxonomic groupings.

BRANCHIAL PLUME   [need definition]. In nudibranchs… See illustration: Composite Nudibranch.

  Point on posteroventral margin of OYSTERS nearest to palliobranchial fusion, commonly forming conspicuously projected posteroventral tip on left valve, especially in sickle-shaped oysters; ABORAL end of GILLS points towards it.

BREATHING PORE   Opening in the MANTLE or mantle edge of SLUGS for passage of air (or often water in aquatic species) into the air sac or lung cavity; see also: PNEUMOSTOME.

BREVICONE   [need definition]; see also: CYRTOCONE; ORTHOCONE.

BRISTLE   A stiff, fine projection. In CHITONS, the GIRDLE may be adorned with bristles. See illustration: Composite Chiton.

BROODER   Term applied to a bivalve or gastropod which retains the young within the parental shell, and liberates them as miniature forms of the adult, or as larvae, but not as fertilized or unfertilized eggs; see also: BIVALVE, BROODING; DEVELOPMENT, DIRECT.

  A mass of bubbles (left image) generated by planktonic snails to keep them at the surface, maintaining accessibility to their prey (e.g., Portuguese Man of War, Physalia; the By The Wind Sailor, Vellella; or the Blue Buttons, Porpita. Also, Janthina creates a bubble raft (right, dual image) to support its EGGS.

Left Photo: Janthina pallida (Thompson, 1840)
Two Right Photos: Janthina sp. upperside and underside of its EGG MASS.

BUBBLE SHELL   A CEPHALASPID OPISTHOBRANCH mollusk. Examples are those species in the genera Bulla and Acteocina.

BUCCAL   Pertaining to the organs of the mouth area. In a gastropod, pertaining especially to the bulging, flexible tissue mass that supports the radula. In cephalopods, the rounded orifice containing the mouth and surrounded by tissue (the buccal membrane) at the base of the arms.

BUCCAL MASS   [need definition]

BUCCAL PUMP   The organ, in the nudibranch family Goniodorididae, which sucks only the juices of its food, the polyzoa and ascidians.

BUCCINOID   Having the shape of shells of the gastropod family Buccinidae. See other gastropod shapes.

BULBOUS   Bulging or globular.

BULLA   The form of a young COWRY (aka Cowrie), before it forms its final whorls and generates APERTURAL TEETH.

BULLOID   Bubble-shaped; in the shape of a shell of the genus Bulla. See also: BUBBLE SHELL.
See other gastropod shapes.

BUTTRESS   A shell-strengthening structure, e.g., a complete or partial supporting ridge. In bivalves, an internal projection from wall of shell, supporting hinge plate or chondrophore; see also: CLAVICLE.

BYNE'S DISEASE   A reaction of shells to acid vapors in the air, resulting in a white powdery residue on the shells. Oak wood is one source of such vapors. One thing to remember about Bynes Disease is that the cause has two components. The development of the condition requires (1) a material capable of releasing acid vapors, and (2) sufficient moisture to allow those acid vapors to form. Some woods, such as oak have the capacity to release such vapors, in the presence of moisture.

If you cannot keep your cabinets in an area free of high humidity, you should be careful about the wood they are made from. But if you have a good dry place to keep the collection, then the type of wood in the cabinets is far less problematic. Good ventilation is a plus, but it is not the deciding factor. If you have an acid-producing wood in a moist environment, then Bynes can occur, even with good ventilation (though probably more slowly than with poor ventilation). If you have the collection is a low humidity environment, then Bynes should not occur, even if the ventilation is poor. It is a good idea to control humidity regardless of what kind of cabinets you have, since high humidity tends to favor other problems as well, especially fungal growth. (Per: Paul Monfils, Conch-L listserve May 21, 2001).

See the Bynes Disease article, (Byne's Disease – Questions and Answers), on the Conchologists of America (COA) web site.

BYSSAL   Pertaining to the BYSSUS.

BYSSAL FORAMEN   Opening in the right valve in Anomiidae for passage of calcified byssus; see also: BYSSAL GAPE; BYSSAL NOTCH; BYSSAL SINUS.

BYSSAL GAPE   Opening between margins of a bivalve shell for passage of the BYSSUS; see also: BYSSAL FORAMEN; BYSSAL NOTCH; BYSSAL SINUS.

BYSSAL NOTCH   Indentation below anterior auricle of right valve in many Pectinacea for passage of the byssus or protrusion of the foot. See illustration: Composite Bivalve. See also: BYSSAL FORAMEN; BYSSAL GAPE; BYSSAL SINUS.

See: Bivalve terminology, Anatomy of bivalves by Marlo Krisberg.

BYSSAL PLUG   [need definition]

BYSSAL SINUS   Embayment of margin below anterior auricle of left valve in many Pectinacea, corresponding to byssal notch of right valve but usually shallower; see also: BYSSAL FORAMEN; BYSSAL GAPE; BYSSAL NOTCH.




  A clump of thread-like, CHITINOUS (usually) filaments secreted by the foot of a MUSSEL or other bivalve which serves to anchor it to the substrate; the byssus of the Anomiidae is CALCAREOUS. See illustration: Composite Bivalve. See also: RADICATED.

CAECUM   A blind pouch or cavity open at one end; see examples in the family Caecidae. See also: MUCRO.

CALCAREOUS   Composed mostly of, or impregnated with, CALCIUM CARBONATE (lime), three forms of which commonly occur in molluscs: ARAGONITE, CALCITE, and VATERITE; see also: CORNEOUS.

CALCITE   A common crystalline form of natural CALCIUM CARBONATE, CaCO3, that is the basic constituent of seashells (as well as limestone, marble, and chalk); see also: ARAGONITE; VATERITE.

= CaCO3
  The mineral, CaCO3, which makes up molluscan shells, occurring in different forms such as ARAGONITE, CALCITE, and VATERITE. See also: PRISMATIC LAYER; PORCELANEOUS LAYER; PRISMATIC LAYER.


CALLOUS   Coated with a smooth enamel-like layer (INDUCTURA).

CALLUM   Shell material filling a gape between valves in certain bivalves. Secondary CALCAREOUS structure present in some Pholadidae, forming anterior extension of shell proper and closing PEDAL GAPE in adult. Example: the MESOPLAX in Martesia striata (Linne, 1758).

CAMEO   A low relief carving into the surface of an object, such as a mollusc shell. Shells of the genus Cassis are often used for such art.

CANAL   In gastropods, a narrow notch or semitubular extension of the aperture, usually enclosing a siphon; see also: CANALICULATE; SIPHONAL CANAL.

CANALICULATE   Having a distinct groove or canal.

CANCELLATE   Having sculptural lines that intersect at right angles; = DECUSSATE; RETICULATE. See illustration: Composite Gastropod and Composite Bivalve. See also: TESSELLATE.
Photo: Chione cancellata (Linne, 1767)

CANTED   Slanted or sloped in relation to an adjoining structure; nonperpendicular.

CAPACIOUS   Large, roomy, spacious; said of the aperture or shell body of gastropods.

(pl. CAPSAE)
  [need definition]

CAP-SHAPED   Broadly conical, as in the shell of LIMPETS; see also: CANTED; PATELLATE; PATELLIFORM. See other gastropod shapes.

CAPTACULA   The cluster of feeding appendages of SCAPHOPODS. See illustration at UCMP.

CARDINAL AREA   In bivalves, situated more or less in the central part of the hinge area, immediately below the BEAKS. Flat or slightly concave, commonly triangular surface extending between beak and hinge margin in many bivalves, and partly or wholly occupied by LIGAMENT.

CARDINAL AXIS   Imaginary straight line along which 2 valves of shell are hinged; = HINGE AXIS.

CARDINAL COSTA   Ridge or rib demarcating cardinal area from outer surface of shell.

(sing. CRUS)
  Narrow lamelliform teeth radiating from apex of LIGAMENT PIT in the Pectinacea.

CARDINAL MARGIN   The edge of a BIVALVE shell on which the HINGE TEETH are located.

CARDINAL PIT   [need definition]

CARDINAL PLATFORM   Shelly internal plate bearing hinge teeth, situated below beak and adjacent parts of dorsal margins and lying in plane parallel to that of commissure; = HINGE PLATE.

CARDINAL TOOTH   The main or largest teeth (usually) in a bivalve HINGE, located just below the UMBONES. See illustration: Composite Bivalve. See also: TOOTH, LATERAL.

CARDO   [need definition]; (see: Popov, 1980).

  A keel-like part; a prominent knife-edged ridge; = KEEL. See illustration: Composite Gastropod. See also: WHORL, CARINATE; WHORL, BICARINATE.

CARINATE   Having a CARINA, especially at the periphery of a WHORL; = KEELED.


CARRIER SHELL   A SNAIL of the family Xenophoridae. These snails attach objects to the periphery of their whorls, thereby "carrying" them.

CARTILAGE   An old term used for the INTERNAL LIGAMENT in bivalves. The substrate on which a radula sits.

CARTILAGINOUS   Having a flexible or HORNY texture, as contrasted with SHELLY or CALCAREOUS.

CAST   The mould from a FOSSIL shell, composed of matter which entered the shell in a soft state and has subsequently hardened, the shell eroded away, and the hardened material left to represent the internal form of the shell. See also ENDOCAST.

CATACHOMATA   pits in the left valve of bivalves for reception of ANACHOMATA; see also: CHOMATA (sing., CHOMA).

CAUDAL CANAL   The elongated, hollow process which terminates the aperture anteriorly, in some gastropod shells (e.g., Murex spp.); = ANTERIOR CANAL; = SIPHONAL CANAL.

CAUDAL PIT   A conspicuous depression in the posterior dorsum of the foot of some snails which contains mucous glands.

CAUDATE   With narrow, tail-like extremity.

CEMENT BODY   Gland near the top of a SPERMATOPHORE containing a glue-like fluid.

CEMENTATION   Permanent fixation to the substrate in sessile molluscs, especially bivalves. See also: ATTACHED.

CENTRAL   At the center; see also: SUBCENTRAL.

CEPHALASPID   An OPISTHOBRANCH gastropod mollusc which possesses a "HEAD SHIELD"; examples include those in the genera Bulla and Acteocina. = BUBBLE SHELL. See also: ANASPID.

CEPHALOPOD   A member of the molluscan class Cephalopoda (once referred to, by Pliny, as Mollia), which is characterized by muscular tentacles attached directly to their head. They have a beaked mouth and their eyes are well developed. This term pertains to SQUID, OCTOPUS, CHAMBERED NAUTILUS, CUTTLEFISH and the extinct AMMONITES and BELEMNITES; see also: TEUTHOLOGIST; TEUTHOLOGY.

See the excellent "Cephalopod Glossary" by Richard E. Young, Michael Vecchione, and Katharina M. Mangold.

CEPHALOTOXIN   A toxin produced by the posterior salivary glands of CEPHALOPODS, used by OCTOPUS to paralyze crabs. See:
Ghiretti, F. 1959. Cephalotoxin: the crab-paralysing agent of the posterior salivary glands of cephalopods. Nature 183:1192-1193 (25 April 1959).

(pl. CERATA)
  On of the slender, club-shaped or horn-shaped dorsal appendages in the NUDIBRANCHIA and ASCOGLOSSA, which either lie separately or in several rows or may be clustered together in tufts and palmate bunched; they contain blood from the HAEMOCOEL and are invaded also by tubular branches of the digestive gland which, as evolution proceeds, becomes deployed on On of the slender, club-shaped or horn-shaped dorsal appendages in the Nudibranchia and Ascoglossa, which either lie separately or in several rows or may be clustered together in tufts and palmate bunched; they contain blood from the haemocoel and are invaded also by tubular branches of the digestive gland which, as evolution proceeds, becomes deployed on the dorsal surface; see also: CLADOHEPATIC; HOLOHEPATIC. See illustration: Composite Nudibranch.

CERATUS   A hornlike structure; a large spur; see also: LABIAL TOOTH.

CF (CONFER)   Sometimes put in front of a species name to mean that the species being identified is close to, but not exactly, a certain species; it also implies that you know for sure that it is not that species mentioned, but merely close to it, e.g., Conus cf. crocatus Lamarck, 1810; (a "?" prior to a species name indicate that the correct name is possibly the one mentioned). See also: AFF (AFFINIS).

CHAETODERM   [need definition].

CHALAZA   An EGG capsule; (see: Franz, 1971:177). See also: NIDAMENTAL GLAND.

CHAMBERED   Having an essentially discontinuous cavity, usually separated by diaphragms or septa, as in the chambers of the CHAMBERED NAUTILUS (chambers also occur in some species of Spondylus and several turrited gastropods); see also: CONCAMERATIONS.


CHANNEL   A deep groove; see also: FLUTED.

CHANNELED   Sculptured with deep grooved; having a groove; see also: FLUTED; STRIATE.

CHARACTER, ADAPTIVE   Those characters which are immediate modifications for a particular mode of life; see also: CHARACTER, PROGRESSIVE; CHARACTER, CONSERVATIVE.

CHARACTER, CONSERVATIVE   Those characters that persist unchanged over long periods. It is these characters that are most useful in showing real affinities of one group toward another; see also: CHARACTER, ADAPTIVE; CHARACTER, PROGRESSIVE.

CHARACTER, PROGRESSIVE   Those characters which usually show a definite trend of advance, often running parallel through several unrelated groups; see also: CHARACTER, ADAPTIVE; CHARACTER, CONSERVATIVE.

CHERRYSTONE   The midsized QUOHOG clam, Mercenaria mercenaria. See also: LITTLENECK.

CHEVRON (GROOVE)   V-shaped furrow on cardinal area in some Arctacea and early Pectinacea, for insertion of the LIGAMENT.

CHIASTONEURY   The condition in the GASTROPOD visceral nerve loop being twisted into a figure-8, during TORSION.

CHINESE HAT SHELL   A shell of the family Calyptraeidae. See also: SLIPPER SHELL; CUP AND SAUCER SHELL

CHINK   A long, narrow cleft, especially in the umbilical area.

CHIRAL   An object having the property of CHIRALITY.

CHIRALITY   An asymmetry property important in several branches of science. An object or a system is called CHIRAL if it differs from its mirror image, and its mirror image cannot superimpose on the original object. A chiral object and its mirror image are called ENANTIOMORPHS (Greek opposite forms) or, when referring to molecules, enantiomers. A non-chiral object is called ACHIRAL (sometimes also AMPHICHIRAL) and can be superimposed on its mirror image. Used in the context of Busycon and the SINISTRAL and DEXTRAL forms.

CHITIN   The general name for a group of HORNY, proteinaceous substances, one of which (CONCHIOLIN) is found in PROTOCONCHS, RADULAE, etc.

CHITINOUS   Chitin-like; composed of CHITIN; see also: HORNY.

CHITON   Common name for members of the molluscan class POLYPLACOPHORA, commonly called COAT OF MAIL SHELLS.
Photo: Acanthopleura granulata (Gmelin, 1791)

A glossary of chiton terms is also available on the Gallery of Chitons website.

CHOMATA   Collective term for ANACHOMATA, which are small tubercles or ridgelets on periphery of inner surface of right valve of bivalves, and CATACHOMATA, which are pits in the left valve for reception of anachomata; both generally restricted to vicinity of the hinge, but may encircle whole valve.

CHONDROPHORE   A pit or spoon-like shelf in the hinge of a bivalve, such as Mactra, and into which fits a CHITINOUS cushion or RESILIUM.. See illustration: Composite Bivalve. See also: LIGAMENT PIT; RESILIFER.

CHRESONYMY   A SYNONYMY that includes misuses of names as well as true synonyms (i.e., most "synonymies").

CHROMATOPHORE   Tiny, elastic, transparent cell fringed with pigment, and responsible for display of coloration; common in CEPHALOPODS.

CICATRIX   Old term for the scar, on the interior of a shell, due to a muscle attachment; see also: MUSCLE SCAR.

CILIA   Minute hairs; see also: MUCOCILIARY FEEDING.

CILIATED   Having minute hairs (or CILIA); see also: MUCOCILIARY FEEDING.

CINEREOUS   Grayish or ash-colored.

  A band or girdle, e.g., a band of color or raised sculpture.

CIRCUMBOREAL   Distributed around the world, in the northern BOREAL region. See also: PROVINCE.

CLADISTICS   [need definition]. See also: CLADOGRAM.

See the Paleos website.

CLADOGRAM   [need definition]. See also: CLADISTICS.

CLADOHEPATIC   Having the "liver" or digestive gland broken up and dispersed throughout the body and often into club-shaped CERATA or fleshy fingers on the DORSUM of OPISTHOBRANCHS. This condition originated independently in various groups and can be used only for identification and not classification; see also: CERATA; HOLOHEPATIC.

CLAM   Common term for a BIVALVE. See also some common names for various types of clams: COQUINA; DATE MUSSEL; GIANT CLAM; MUSSEL; OYSTER; PIDDOCK; QUAHOG; RAZOR CLAM; SHIPWORM.


CLASSIFICATION   An arrangement or hierarchy of animals and plants into taxonomic groups; i.e., grouped according to their similarities; see also: TAXONOMY; SYSTEMATICS.

CLATHRATE   Having intersecting sculptural elements forming a broad lattice.

  A CALCAREOUS, loose "sliding door" in the Clausiliidae (Pulmonata) which fits into the grooves of the COLUMELLA, serving as a door. When not prevented by counteracting pressure, the clausilium springs forward on its elastic LIGAMENT and encloses the animal into its shell.


CLAVATE   Having one extremity of a shell attenuated and the other suddenly VENTRICOSE or GLOBULAR.

CLAVICLE   Shelly buttress supporting a CHONDROPHORE in some genera.

CLEIDOIC   A type of egg which is not impermeable to water (the cytoplasm of the egg is adapted to tolerate a considerable water loss, rather than the shell to prevent it).

CLOSED   In bivalves, having the valves meet tightly along the entire margin; see also: GAPE; GAPING.

CLOSURE SEAM   A line of junction; a line, groove, or ridge formed by or between abutting edges.

CLUB   In squid, the expanded area (generally bearing large suckers) on the distal end of the tentacle.

CLUB-SHAPED   In a GASTROPOD shell, having a compact, rounded body and a long SIPHONAL CANAL.

COALESCED   Fused or merged together.

COAT OF MAIL (SHELL)   Common name applied to CHITONS (the molluscan class Polyplacophora), due to their resemblance to jointed armour.

COCHLEATE   Being hollow and oval, like a spoon, e.g., the LIGAMENT PIT of Mya spp.

COELOCONOID   Slightly concave; see also: CYRTOCONOID.
See other gastropod shapes.

COELOM   [need definition].

COFFEE BEAN SNAIL   A GASTROPOD of the genus Melampus.

COGNATE   Of, or proceeding from, the same stock; allied; of the same or similar nature, as in the case of closely related forms or species on both sides of the Central American isthmus.

COILING   In gastropods, the wrapping of one WHORL around a previous whorl; see also: LOGARITHMIC SPIRAL; LOOSELY COILED; TIGHTLY COILED.

COLL.   An abbreviation for the latin, Collegit, meaning: Collected by. However, this abbreviation is also interpreted as: In the collection of. Because of this ambiguity, the use of LEG. is preferred over COLL.

COLLABRAL   Parallel or nearly so. See also: COLLABRAL LINES.

COLLABRAL LINES   A series of similar, adjacent lines. See also: GROWTH LINE.

COLLAR   A raised rim bordering a suture. In cephalopods, the free edge of the mantle in squids, etc., at the "neck."

COLUMELLA   A pillar surrounding the AXIS around which the shell is coiled, formed by the inner surface of the WHORL; the wall opposite the outer APERTURAL LIP. See illustration: Composite Gastropod. See also: AXIS; PILLAR.

COLUMELLA, STRAIGHT   [need definition].

COLUMELLA, TRUNCATE   [need definition].

COLUMELLAR   Pertaining to the COLUMELLA.

COLUMELLAR CALLUS   A smooth, shelly layer extending over the COLUMELLAR area, secreted by the mantle; see also: PARIETAL CALLUS.

COLUMELLAR FOLD   A raised ridge on the COLUMELLA that follows the helical growth pattern of a gastropod shell.; see also: FUNICLE.

COLUMELLAR LIP   The part of the inner lip, of a gastropod shell, nearest to the axis of coiling, and comprising the visible part of the COLUMELLA.

COLUMELLAR PLAIT   [need definition]. See illustration: Composite Gastropod.

COLUMELLAR PLICAE   [need definition]. See illustration: Composite Gastropod.

COLUMELLAR TOOTH   A sharply raised projection, emanating from the COLUMELLA and protruding into the APERTURE of a GASTROPOD. See illustration: Composite Gastropod.


COMMARGINAL   [need definition].

COMMARGINAL RIB   [need definition]; see also: OVERRIDE.

COMMENSAL   The association of one species with a different species in which one or more is benefitted, and others are not harmed. See also: PARASITE.

COMMISSURE   Line of junction of 2 VALVES of a BIVALVE.


COMPLANATE   Flattened; level; unsculptured; see: COMPRESSED.

COMPRESSED   Flattened, typically laterally (opposite of DEPRESSED); having reduced thickness or height; see: COMPLANATE.

CONCAMERATIONS   A series of chambers joining each other, as in Nautilus spp.; see: CHAMBERED; PHRAGMOCONE.

CONCAVE   Hollowed and curved or rounded; opposite of convex; see also: COELOCONOID; CYRTOCONOID.

CONCAVITY   The quality or state of being CONCAVE; a concave point.

CONCENTRIC   Having a common center, as circles. In gastropod shells, said of structures roughly parallel to growth lines (referred to as LONGITUDINAL by some authors); see also: ANNULATE; TRANSVERSE. The term COMMARGINAL is preferred by some modern authors. See also: ECCENTRIC.

CONCENTRIC LINE   See: GROWTH LINE. See illustration: Composite Bivalve.

CONCENTRIC SCULPTURE   [need definition]; see also: AXIAL SCULPTURE.

CONCH   A COMMON NAME referring to a member of the gastropod family Strombidae. Also, and generally, a seashell; see also: ANIMAL. People that study seashells (conchs) are CONCHOLOGISTS.
Note: Although the "Florida Horse Conch" (Triplofusus giganteus (Keiner, 1840)) is so named, it is a misnomer and is more properly called a "Horse Whelk," as it is in the whelk family: Fasciolariidae.

CONCH PEARL   A PEARL, often pink in color, produced by the Queen Conch, Strombus gigas.

CONCHIOLIN   A HORNY, proteinaceous material that makes up the periostracum of a shell and also forms the organic matrix for calcareous parts of the shell; often termed CHITIN; see also: PRISMATIC LAYER; CALCITE; ARAGONITE; VATERITE.

CONCH-L LISTSERV   A mailing list on a LISTSERV supported by the University of Georgia (UGA). Members subscribe to "the list" to facilitate an easy exchange of emails via "posting" one email to "the list" which is distributed by the Listserve to all subscribers of the list to which the initial email was sent.

See the compilation of information about Molluscan Listserves.

CONCHOLOGIST   A specialist in the study of molluscan shells (CONCHS). A group organized to share such interests is the CONCHOLOGISTS OF AMERICA (COA). See also: MALACOLOGIST; TEUTHOLOGIST.

CONCHOLOGISTS OF AMERICA (COA)   A group organized to share interests in CONCHOLOGY and which describes itself on the COA website as a "society for shell enthusiasts from all walks of life, at all levels of interest." This organization publishes American Conchologist. See also: MALACOLOGICAL SOCIETY; SHELL CLUB.


CONCHOMETRY   [need definition]. See references:
Boycott, A.E. 1928. Conchometry. Proc. Malac. Soc. London 18:8-31.
Parodiz, J.J. 1951a. Me´todos de conquiliometry #305;´a. Physis 20(58):241–248.
Parodiz, J.J. 1973e. Gastropod conchometry. Pittsburgh Shell Club Bulletin 8:14–16.

CONDYLE   An enlarged and prominent end of a RIDGE, serving as a pivot.

CONE SHELL   Common name applied to a SNAIL of the genus Conus. See also: CONOTOXIN.
Also, see: The Conus Biodiversity Website.

CONFLUENT   Coming together; merging; see also: COALESCED.

CONGENER   A species belonging to the same genus as the species used as a point of reference; see also: CONSPECIFIC.

CONGENERIC   Belonging to the same genus as the species used as a point of reference; see also: CONGENER.

CONICAL   Cone-shaped; tapering; see also: BICONIC; CONICAL; CYLINDRICAL.
See other gastropod shapes.

CONMARGINAL   Preferred term by some modern authors for structure with direction coinciding with that of growth lined; = CONCENTRIC, in bivalves.

CONOTOXIN   A neurotoxin produced by the venom gland of GASTROPODS of the genus Conus; often referred to as CONE SHELL venom.

CONSPECIFIC   Of the same species as an organism used as a point of reference; see also: CONGENER; CONGENERIC.

CONSTRICTED   Marked by a more or less abrupt narrowing; waist-like; pinched.

CONSTRICTION   A narrowed area.

CONTIGUOUS   Touching each other, as in the WHORLS of some gastropods in which the whorls rest upon or touch each other; see: DISCONTIGUOUS; DISCONTINUOUS; DISTAL; PROXIMAL.

CONTINUOUS   Uninterrupted; intact from one point to another; see: CONTIGUOUS; DISCONTINUOUS; HOLOSTOMATE; SIMPLE.

CONTRACTED   Drawn together; reduced in extent; shrunken.

CONTRACTILE   Capable of reducing length by shortening and thickening; see also INVERSIBLE.

CONVEX   Curved or rounded; bulging outward; opposite of CONCAVE; see also: CYRTOCONOID.

CONVEXITY   Degree of inflation.

CONVOLUTE   Having the body whorl of the shell expand abruptly so as to wrap around and conceal all the older, subsequent whorls. See also: INVOLUTE. See other gastropod shapes.

COPULATORY ORGAN   Usually a penis or other organ used by the male to insert sperm into the female; see also: VERGE.

COQUINA CLAM   Common name for CLAMS of the genus Donax.

CORBICULOID TYPE   Heterodont dentition (in bivalves) with 3 cardinal teeth in each valve, middle one of right valve occupying median posterior position below BEAKS; formerly termed CYRENOID TYPE.

CORBULIFORM   Shaped like the shells of the bivalve genus Corbula.

CORD   A thickened round-topped transverse (i.e., spiral) or axial sculptural element.

CORDATE   Shaped like a heart; often applied to shells such as Cardium, Cardita, and Venus; see also: CORDIFORM; SEMICORDATE.

CORDED   Sculptured with cords.

CORDIFORM   Heart shaped, as in the bivalve Corculum cardissa. See also: CORDATE.

  HORNY in texture and composition; see also: CALCAREOUS.

CORONA   A crown-like structure; see also: CORONATE.

CORONATE   Crown-like; having a CORONA; encircled by a row of spines or prominent nodes, especially at the shoulder of the last whorl in gastropods.

CORRODED   Worn away (usually with age), as in the UMBONES of some bivalves or SPIRES of some gastropods; see: DECOLLATE; OBSOLETE.

CORRUGATE   Folded or ridged on the surface; broadly or heavily sculptured with FOLDS.

CORSELET   A differentiated (by sculpture) POSTERIOR area of a BIVALVE.

(pl. COSTAE)
  A round-topped sculptural element, stronger than a cord, usually formed by periodic thickening of the outer lip in gastropods. Moderately broad and prominent elevation of surface of shell, directed radially or otherwise; see also: COSTELLA.

COSTATE   Having rib-like AXIAL sculptural elements.
See illustration: Composite Gastropod and Composite Bivalve.

COSTELLA   Rather narrow linear elevation of surface of shell; formerly: COSTULE; see also: COSTA.

COSTULATION   A pattern of sculpture in small RIDGES.

COSTULE   Old term for COSTELLA.

COWL   A hood; a fold-like structure extending over the front or outward like a hood.

  Common name applied to gastropods in the family Cypraeidae. See also: BULLA.

CRABBED   A gastropod shell, usually in poor condition, formerly used as a home for a hermit crab (Crustacea: Paguridae). The columella may have a U-shaped worn area.

CRENATE   Having a regularly notched or scalloped edge; see also: CRENULATE.

  Same as CRENATE, but implying smaller or finer divisions. See illustration: Composite Bivalve. See also: DENTICULATION

CRENULE   Small notches or beads.

CREST   The apex of a peak or ridge; the top of a sculptural element.

CRISPATE   Irregularly curled; roughened into small frets, waves, or folds.

CROSSED-LAMELLAR   Type of shell structure comprised of primary and secondary LAMELLAE, the latter inclined in alternate directions in successive primary lamellae.

CRUMPLED   Creased or pressed into wrinkles or folds.

CRURAL   Pertaining to CRURA.

(pl. CRURA)
  Pairs of diverging ridges on the hinge of some bivalves, resembling teeth.

CRYPTODONT   Lacking HINGE TEETH (applied to certain groups of early origin only); see also: EDENTULOUS; EDENTATE; ANODONT.

CRYSTALINE STYLE   [need definition]. In bivalves...



CTENOLIUM   Comb-like row of small teeth on the lower side of BYSSAL NOTCH in some Pectinacea.

See: Bivalve terminology, Anatomy of bivalves by Marlo Krisberg.

CUNEIFORM   Wedge-shaped.

CUP AND SAUCER SHELL   A shell of the family Calyptraeidae. See also: SLIPPER SHELL; CHINESE HAT SHELL

CURVED   Arched or gently bent; = ARCUATE.

CUSP   A prominence or point, especially on a RADULAR TOOTH or a DENTICLE on the shell.

CUSPIDOBLAST   One of the cells in a CAECUM or pouch at the posterior of the RADULA which secrete the radular teeth.

CUTICULAR SHIELD   In Aplacophorans…

  The internal shell of the CUTTLEFISH (Cephalopoda), Sepia officinalis. See also: BELOPTERA.

CUTTLEFISH   [need definition]. A CEPHALOPOD… See also: BELOPTERA.

CYATHIFORM   Cup-shaped (as in the "cup" of "cup and saucer" limpets, the Calyptraeidae).

CYCLODONT   BIVALVE DENTITION with HINGE TEETH curving out from below HINGE MARGIN, HINGE PLATE being small or absent.

CYLINDRICAL   Like a cylinder; applied to shells with sides which are nearly parallel, with the extremities either rounded, flat or conical. See also: CONICAL. See other gastropod shapes.

CYPRAEIFORM   A shape exemplified by the gastropod genus Cypraea. See other gastropod shapes.



CYRTOCONE   In cephalopods, laterally compressed, curved shells; see also: BREVICONE; ORTHOCONE.

CYRTOCONOID   Slightly convex. See also: COELOCONOID. See other gastropod shapes.

DART SAC   A muscular caecum developed from the vagina in which is produced a fine, pointed, calcareous shaft, the TELUM AMORIS, or "love dart;" see also: SARCOBELUM.

DATE MUSSEL   Common name applied to CLAMS of the genus Lithophaga. See also: MUSSEL.

DEAD SHELL   Term applied by collectors to a shell which did not have a live animal in it when collected; see: LIVE SHELL.

DECK (1)   A small sheet of SHELLY substance in the UMBONAL region of a valve; see also: DECK (2).

DECK (2)   The diaphragm of slipper shells (Crepidula spp.), sometimes called the SHELF; see also: DECK (1).

DECOLLATE   Cut off; TRUNCATED, e.g., the top several whorls of the spire (as in Truncatella spp.); typically, the loss of this portion of the shell is by design, rather than wear or corrosion; see: CORRODED.

DECORTICATED   Missing the NACRE and/or true coloration.

DECURRENT   Extending downward; see also: DEFLEXED.

DECUSSATE   Having intersecting sculptural elements, not necessarily at right angles; RETICULATE. See illustration: Composite Gastropod and Composite Bivalve. See also: CANCELLATE; LATTICED.

DEFLEXED   Bent sharply backward or downward; see also: DECURRENT; RECURVED; REFLEXED.

DEHISCENT   Capable of falling off very easily; often used in reference to the PERIOSTRACUM; see also: EXFOLIATE.

DELIMITING   Bounding; fixing a limit.


DEMARCATION LINE   In bivalves, an imaginary line on the surface of valve originating at the BEAK and marking locus of points on successive positions of margin where transverse growth component has had maximum effect; forms dorsoventral profile when VALVE is viewed from one end; see also: CORSELET; DIAGONAL RIDGE; ESCUTCHEON RIDGE.

DEMIBRANCH   One of the paired lamellibranch gills. The longitudinal half of a feather-shaped gill; see also: DIBRANCH; TETRABRANCH.


DENTATE   Toothed; having HINGE TEETH; having a toothed margin; see also: DENTICULATE; TRIDENTATE.

DENTICLE   A small, tooth-like projection.

DENTICULATE   Having small, tooth-like projections; see also: DENTATE; SERRATE.

DENTICULATION   The overall pattern of DENTICLES in a given shell or specimen.


DEPAUPERATE   Poorly developed.

DEPRESSED   Pressed down, typically dorso-ventrally (opposite of COMPRESSED); low in proportion to diameter.; see also: DISCOIDAL.

DEPRESSION   A hollowed area; a concavity.

  Identified by. Example on a specimen label: Det: John Doe; or: John Doe, det. See also: LEG.

DETACHED   Separated; marked off; see also ATTACHED.

DETORSION   [need definition]. See also: TORSION.


DEVELOPMENT, DIRECT   Passing the entire larval stages within an egg case or within the adult; lacking a free-swimming or floating larval stage; see also: BROODER; DEVELOPMENT, PLANKTONIC.


DEVOLUTE   [need definition]; see also: LOOSELY COILED.

DEXTRAL   Turning clock-wise or to the right, or "right-handed" in gastropods; the direction of coiling in which, with the shell held upright (apex at the top), the aperture is at the right; and in which, with the shell viewed from above the apex, the coiling proceeds from the apex in clockwise direction; = RIGHT HANDED.; opposite of SINISTRAL; See also: CHIRALITY; ENANTIOMORPH; HETEROSTROPHY; ULTRADEXTRAL.
See other gastropod shapes.

DIAGENODONT   Bivalve DENTITION with differentiated CARDINAL and LATERAL TEETH located on HINGE PLATE, laterals not exceeding 2 or cardinals 3 in either valve; example: Astarte spp.; see also: TELEODONT.

DIAGNOSIS   A short, comparative description of a SPECIES.

DIAGNOSTIC   Central to identification; especially characteristic; reflecting critical comparative scrutiny.

DIAGONAL RIDGE   In bivalves, a ridge running from the UMBO toward posteroventral part of VALVE; see also: CORSELET; DEMARCATION LINE.

DIAMETER   The greatest width of a snail shell at right angles to the shell axis. See illustration: Composite Gastropod. See also: WIDTH; WRS.


DIAPHRAGM   The septa which divide the chambers of MULTILOCULAR and other shells. Also, the DECK of SLIPPER SHELLS.

DIBRANCH   Possessing two gills (CTENIDIA); the name applied to all living cephalopods, except Nautilus, which is a TETRABRANCH; see also: EULAMELLIBRANCH; FILIBRANCH; LAMELLIBRANCH; PROTOBRANCH; PSEUDOLAMELLIBRANCH; SEPTIBRANCH; TECTIBRANCH.

DIFFUSE   Spread out; applied to the APERTURE of a gastropod shell which is widened into a flat surface; = ALATE; = DILATED.

DIGESTIVE GLAND   [need definition].

DIGITATE   In a finger-like fashion; having finger-like processes.

DIGITATION   A finger-like part; a pattern of finger-like parts.

DILATED   Expanded or spread; = ALATE; = DIFFUSE.

DIMORPHISM   Having two forms, e.g., differing forms for different sexes = sexual dimorphism; see also: POLYMORPHISM.

DIMYARIAN   The condition in bivalve molluscs of having two ADDUCTOR MUSCLES, the anterior and posterior; see also: ANISOMYARIAN; HETEROMYARIAN; MONOMYARIAN.

DIOECIOUS   Having the male and female sexes separate; see also: AMBISEXUAL; HERMAPHRODITE; MONECIOUS; PROTANDRY.

DIOTOCARDIAN   Having a heart with two auricles. See also: MONOTOCARDIAN.


DIRECTIVE SPIRAL   Spiral curve formed by DIRECTIVE RIB within its own plane.

DISC   The VALVES of bivalves; in Pectinacea, the whole of the valve, excluding the AURICLES; see also: FLANK.

DISCOIDAL   Round and flat, like a disk.; see also: DEPRESSED; LENTICULAR; PLANISPIRAL; SEMIDISCOIDAL. See other gastropod shapes.

DISCONTIGUOUS   Not touching each other, as in the whorls of some gastropods in which the whorls are separated and do not rest upon or touch each other; see: CONTIGUOUS; CONTINUOUS; WHORL, DISJUNCT; GYROCONIC.

DISCONTINUOUS   Interrupted; not continuing intact from one point to another; see: CONTINUOUS.

DISSOCONCH   The postlarval shell of bivalves (and scaphopods?). See illustration: Composite Bivalve. See also: MESOCONCH; NEPIOCONCH; PRODISSOCONCH.

DISTAL   Situated away from the base or point of attachment; = DISTANT; opposite of PROXIMAL; see also: CONTIGUOUS.

DISTANT   See: DISTAL; see also: REMOTE<.a>.

DIVARICATE   Having the sculpture composed of pairs of rather widely divergent COSTAE or threads, as in the genus Divalinga. See illustration: Composite Bivalve. See also: LATTICED; SCISSULATE; TRANSVERSE.
Photo: Divalinga quadrisulcata (d'Orbigny, 1846)

DOCOGLOSSATE   Having a radula in which the RACHIDIAN TOOTH is small or absent, and there are 3 LATERAL TEETH with hard, black tips, flanked by 3 smaller, unpigmented MARGINALS on each side; = STEREOGLOSSATE; examples in the Patellacea: Acmaeidae, Lepetidae, Patellidae; RADULAR FORMULA: 3+D+2+R+2+D+3 or 3+D+2+0+2+D+3 (where R = RACHIDIAN, D = DOMINANT DENTICLE).

DONACIFORM   A form of TRIGONAL shape exemplified by the BIVALVE genus Donax. See other bivalve shapes.

DORATOPSIS   The LARVAL stage of the CEPHALOPOD family Chiroteuthidae.

DORSAL   Of, pertaining to, or situated on the back or upper surface; in bivalves, at or toward the HINGE; see also: VENTRAL.

DORSUM   The DORSAL surface of a shell or animal. The "back" of a gastropod shell, opposite the APERTURAL side.


DRAP MARIN   The French naturalist term for periostracum.

DRUPE   Common name applied to gastropod shells of the genus Drupa.

DUPLIVINCULAR   The type of bivalve LIGAMENT with lamellar component repeated as a series of bands, each with its 2 edges inserted in narrow grooves in cardinal areas of respective valves; example: Arca; see also: ALIVINCULAR; PARIVINCULAR; MULTIVINCULAR.

DWARF   Of less than usual or normal size for a given stage of development.

DYMANTIC   Referring to a response to fear or disturbance, characterized by changes in coloration (in the cephalopoda) and appearance.

DYSODONT   In bivalves, a HINGE with small, weak teeth close to BEAKS (as in some Mytilacea).


EAVES   In CHITONS, the portions of the TEGMENTUM just over the points where the INSERTION PLATE and sutural laminae push from under it.

ECCENTRIC   Not having the same center; not CONCENTRIC; deviating from the center, as in an elliptical orbit. In the gastropod shell, not following the GROWTH LINES.

ECHINOSPIRA   A type of VELIGER, in the Lamellariidae, Cypraeidae (Eratoinae) and Capulidae [all Gastropoda], in which the young definitive shell is covered by a much larger secondary shell, the SCAPHOCONCHA, which has practically no weight and assists in floatation during the long swimming life of a larva.; see: LARVA.

ECOLOGIC FORM   A morphological condition brought about by the influence of the environment, such as long SPINES in quiet waters; also called: ECOTYPE or ECOPHENOTYPE. See also: FORM or FORMA

ECOMORPH   One whose morhology is determined by the ecology; = ECOPHENOTYPE.

ECOPHENOTYPE   An organism whose visual characteristics (PHENOTYPE) have been influenced by the environment. Example: a shell having longer spines due to growing in calm waters vs. having short or no spines due to life in fast-flowing waters. See also: ECOMORPH; ECOPHENOTYPIC VARIATION; FORM; GENOTYPE.

ECOPHENOTYPIC VARIATION   Variation caused by environmental conditions. Such variability has been use by SPLITTERS to distinguish one "species" from another. See also: ECOLOGIC FORM; ECOPHENOTYPE.


ECTOPARASITE   Living PARASITICALLY on the outside of another organism; for example, the Pyramidellidae.

EDENTATE   Toothless; same as ANODONT, in bivalves.



EGG   A female gamete or reproductive body; an ovum. See also: CHALAZA; EGG MASS; EGG CAPSULE.


EGG MASS   A cluster of EGGS, sometimes deposited by an individual, but sometimes by multiple individuals contributing to a single mass (e.g., some Muricids). For a PELAGIC example, see: BUBBLE FLOAT.
Photo: Murex pomum Gmelin, 1791

ELEPHANTS TUSK   Common name applied to SCAPHOPOD shells of the genus Dentalium, due to their similar appearance to an elephants tusk; = BOARS TUSK or, generally, TUSK SHELL.

ELEVATED   ERECT; raised; said of prolonged sculptural elements and other structures; see also: DEPRESSED.

ELLIPTICAL   Like an ellipse or flattend oval; see also: ELONGATE ELLIPTICAL.
See other bivalve shapes

ELONGATE   Lengthened; extended in one dimension. Illustration: Solen sp. See also: ENSIFORM; LINGUIFORM.
See other bivalve shapes.
Photo: Tagelus divisus (Spengler, 1794)

ELONGATE ELLIPTICAL   A basically ELLIPTICAL shape that has been elongated; like a flattened oval.
See other bivalve shapes.

EMARGINATE   Notched at the MARGIN.

EMBAYMENT   An indentation; a bay. Sometimes used referring to the PALLIAL SINUS in bivalves.

EMBRYONIC WHORL   A single WHORL of the NUCLEUS or PROTOCONCH; the earliest portion of the LARVAL SHELL.

ENANTIOMORPH   A mirror image of another; perhaps said of two GASTROPOD specimens of a single species, one specimen which has a SINISTRAL shell and one which has a DEXTRAL shell.

ENCRUSTED   Covered with foreign matter derived from living organisms.

ENDEMIC   Confined to a particular geographic area; native; see also: INDIGENOUS.

ENDOCAST   A FOSSIL formation created by material entering the interior of a shell hardening; the exterior shell material then degrades and dissolves away with the outside of the CAST taking on the interior shape of the shell; = STEINKERN.

ENSIFORM   An ELONGATE bivalve shape, like an Ensis; with outline resembling a curved sword. See other bivalve shapes.

ENTIRE   Continuous; having no breaks; said of the margin (PERISTOME) of a shell aperture; see also: HOLOSTOMATE.

EPIDERMIS   Skin of the soft part (= "ANIMAL") of a mollusk; see also: PERIOSTRACUM.

EPIPELAGIC   The PELAGIC depth zone 0 to 200 meters. See also: PELAGIC; MESOPELAGIC (200-1000m depth); BATHYPELAGIC (1000-4000m depth; ABYSSOPELAGIC (4000-6000m depth; HADAL (greater than 6,000m depth); NERITIC; OCEANIC; BENTHIC; PLANKTONIC.

EPIPHRAGM   A temporary apertural seal of dried mucous constructed prior to AESTIVATION to prevent loss of moisture; found in the higher PULMONATE gastropods, such as Helicidae. The epiphragm may become very thick and even calcified, as in the Achatinidae.

EPIPODIUM   A fringe, like a false MANTLE, around the base of the gastropod foot, which bears delicate tentacles that come in contact with the substratum and are probably both chemosensory and tactile.

EQUILATERAL   In bivalves, having the anterior and posterior ends of equal size; see also: EQUIVALVE; INEQUILATERAL; SUBEQUILATERAL.

EQUIVALVE   In bivalves, having each VALVE equal in size and shape; see also: EQUILATERAL; INEQUIVALVE.
See other bivalve shapes.

ERECT   Upthrust or upright; see also: ELEVATED.

ERODED   Worn away; see also: BEACHWORN.

ESCARGOT   Common name for SNAILS, typically of the genus Helix (often H. pomatia, but also H. aspersa and H. lucorum), which are an epicurean delicacy cooked in a garlic and butter sauce and served as an appetizer.

ESCUTCHEON   In bivalves, a long, somewhat depressed area on the dorsal surface just posterior to the BEAKS. See illustration: Composite Bivalve. See also: LUNULE.

See: Bivalve terminology, Anatomy of bivalves by Marlo Krisberg.

ESCUTCHEON RIDGE   Ridge extending posteriorly from beak in each valve (of bivalves) and forming border of ESCUTCHEON; see also: DEMARCATION LINE.

ESOPHAGUS   The tubular portion of the digestive tract that leads from the PHARYNX to the stomach.

ESTUARINE   Pertaining to or living in salt water which is measurably diluted with fresh water (to decrease the salinity below oceanic levels: 35 parts per thousand); see also: AQUATIC; FRESH WATER; HABITAT; MARINE; OCEANIC.


EUPYRENIC   The numerous, small, normal type of SPERM; see also: OLIGOPYRENIC.

EUTHYNEUROUS   Having straight visceral nerve loops (as in some gastropods); see also: STREPTONEUROUS.

EVANESCENT   Transient; ephemeral; barely discernable.

EVOLUTE   [need definition]; see also: DEVOLUTE.


EVOLUTION, CLANDESTINE   The development of many structures by the larvae for its own needs, as distinct from the morphology of the adult; as such, larvae are not always reliable guides to PHYLOGENY; see also: ONTOGENY.

EVOLUTION, PROGRAMME   Having several independent groups running through a series of broadly similar changes.

EX   From; example: Ex Doe, MS. = from Doe's manuscript or unpublished work; ex pisces = from the stomach (usually) of a fish.

EXCAVATED   Strongly depressed; hollowed out.

EXCERTED   Prominently extended or elongated; = EXSERTED.

EXCURRENT   Forming a passage for current of water expelled from within the MANTLE CAVITY; applied to mantle opening or siphon; = EXHALENT; see also: HYPONOME.

EXFOLIATE   To come off in layers or scales. See also: DEHISCENT.

EXHALANT SIPHON   [need definition]; see also: HYPONOME; INHALANT SIPHON.


EXOGASTRIC   In CEPHALOPODS, having the hyponomic sinus on the convex side.

EXOGYRATE   Shaped like the shell of Exogyra, that is, with the left valve (of bivalves) strongly convex and its dorsal part coiled in posterior direction, with right valve flat and spirally coiled.

EXPANDED   Enlarged; swollen; distended; see also: COMPRESSED.


EXTANT   Living; typically referring to a SPECIES or taxonomic group of species; opposite of EXTINCT.

EXTENDED   In gastropods, the state of the animal being exposed out of its shell; also the condition of its TENTACLES being out and functioning or (in NUDIBRANCHSs) a branchial BRANCHIAL PLUME being exposed. In bivalves, the condition of the clam having its FOOT and/or SIPHONS exposed during digging or feeding, respectively. See also: RETRACTED.

EXTERNAL   On the outside; see: INTERNAL.

EXTINCT   No longer continuing to exist, typically referring to a SPECIES or a taxonomic group of species; opposite of EXTANT.

EXTRA-BRANCHIAL APPENDAGE   [need definition]. In NUDIBRANCHS… See illustration: Composite Nudibranch.

EXTRAPALLIAL FLUID   That fluid between MANTLE and the PERIOSTRACUM, which is rich in CaCO3 in solution, which precipitates out, forming the shell.

EYE STALK   The extensible and retractable (sometimes INVERSIBLE) pedestal which terminates with the eye of many gastropods. See also: TENTACLE.

FAIR   Term used in shell trade to designate the quality of a shell as having either major breaks or poor coloration; see also: GRADING SYSTEM.

FALCIFORM   Sickle-shaped.

FAN SHAPED   A CLAM (bivalve) shape exemplified by the bivalve genus Atrina. See other bivalve shapes.
Photo: Atrina rigida (Lightfoot, 1786)

FASCIATE   Banded or striped. See also: BANDING.

FASCICLE   Small bunch (of RIBS); see also: FASCICULATED.

FASCICULATED   Having a little bunch of hairs or BRISTLE against each end of each VALVE (as in some species of the genus Chiton). Arranged in small bunches; see also: FASCICLE.

FASCIOLE   A spiral band generated by a notch, bordered by successive lamellar growth striae of a canal (either anterior or posterior) in gastropods; see also: SIPHONAL FASCIOLE.

FATHOM   A measure of water depth, equal to six feet.

FAUNA   The animal life living in a given region or during a specified period of time.

FENESTRATE   Having depressed, rectangular, pit-like "windows."

FERRUGINEOUS   Of an iron rust color.

FIDE   Trusting to; on the word of; often used to document the designation of a SYNONYM.

FILIBRANCH   A type of bivalve CTENIDIUM or gill in which [need definition]. The Mytilacea, Pteriacea, Pectinacea, and Anomiacea have filibranch CTENIDIA. See also: DIBRANCH; EULAMELLIBRANCH; LAMELLIBRANCH; PROTOBRANCH; PSEUDOLAMELLIBRANCH; SEPTIBRANCH; TECTIBRANCH; TETRABRANCH.

  A border or fringe; see also: FIMBRIATE; FIMBRIATION.

  Fringed; bordered by fine, frilly sculptural elements; = FIMBRICATED; see also: FIMBRIA; FRILLED; LACINIATE.

FIMBRIATION   A fringe; see also: FIMBRIA.

FIN, LATERAL   Fleshy projections on the each side of the mantle of squids.

FINE   A term used in the shell trade to designate the quality of a shell as having minor breaks or scars; see also: GRADING SYSTEM.

FINE+   A term used in the shell trade to designate the quality of a shell as very slightly irregular. See also: GRADING SYSTEM.

FISSURE   A slit or cut. See also: GROOVE.

FLABELLIFORM   Fan-shaped.

FLAGELLUM   A tubular outgrowth of the PENIS in which the SPERMATOPHORE is secreted by the male duct.


FLAMULE   A small, flame-shaped spot of color; = FLAMULATION; see also: FULGURATE.
Photo: Astyris lunata (Say, 1826)

FLANGE   A rib or flattened ridge lending strength and reinforcing the juncture of two shell structures.

FLANK   Median part of surface of valve (of a bivalve), limited posteriorly by posterior ridge where present; see also: DISC.

FLARING   Opening or spreading outward rapidly, said especially of the outer APERTURAL LIP.

FLATTENED   Level; even.

FLEXICLAUDENT   A type of OPERCULUM that flexes upon retraction. See also: RIGICLAUDENT.

See the 1998 article by Checa and Jiménez-Jiménez: Constructional morphology, origin, and evolution of the gastropod operculum..

FLEXUOUS   Having windings or bendings (e.g., the posterior twist of Macoma spp.); see also: HAMIFORM; RECURVED.

FLEXURE   A bending or angulation.

FLUTED   Grooved; decorated with flutes or CHANNELS.

FLUVIATILE   Living in or belonging to rivers or streams; see also: AQUATIC.

FOLD   A spirally wound ridge on the COLUMELLAR WALL of the gastropod shell.; see also: COLUMELLAR FOLD; PLAIT; PLICAE; RUGA.

FOLIACEOUS   Resembling foliage; furnished with or made up of foliations or leaflike small plates; = FOLIATE; FOLIOSE.


FOLIATION   A single leaflike structure; see also: FROND; FOLIACEOUS.


FOOT   A muscular organ of locomotion, projecting anteriorly through the APERTURE of shelled GASTROPODS (often for crawling); see also: LANMGUIR TROTH; PARAPODIA.

In BIVALVES, a organ lying anteroventrally between the VALVES of many bivalves (often for digging).

In SCAPHOPODS, an anterior organ also used for digging; See illustration at UCMP.

FORAMEN   A round hole or fissure; usually applied to the hole in the LOWER VALVE of Anomia spp. which exists for passage of the BYSSAL PLUG.
Photo: Anomia simplex Orbigny, 1842

FORM or FORMA   A minor genetic variant, color phase, aberration, or variation due to diet or environment (e.g., an ECOLOGIC FORM); see also: ECOPHENOTYPE; ECOPHENOTYPIC VARIATION; ECOTYPE; VARIETY.

FORNICATED   Arched or vaulted (e.g., exfoliations on the COSTAE of Tridacna spp.)

FOSSA   A ditch-like or trench-like depression; see also: FURROW; SCROBICULATE; SULCATE.

FOSSETTE   A pit-like resilifer for the attachment of the internal ligament; a socket, as for cardinal tooth in bivalves; see also: CHONDROPHORE; RESILIFER.

FOSSIL   The remains of an animal (or plant) from past ages; see also: CAST; ENDOCAST; TAPHONOMY.

FOSSULA   A shallow linear depression on the inner LIP of some cypraeid gastropods.

FRAGILE   Tender, easily broken; delicate.

FREAK   A malformed shell; see also: GRADING SYSTEM.

FREE   Refers to a shell which is not ATTACHED (e.g., to substrate); see also: VALVE, FREE.

FREE EDGE   The outer margin or OUTER APERTURAL LIP of a gastropod shell.

FREE VALVE   In attached bivalves, the valve which is not attached to the substrate; = UPPER VALVE.

FRESH WATER   Rererring to those which inhabit rivers and streams (= FLUVIATILE), ponds and lakes; see: ESTUARINE; MARINE.

FRILL   See: EPIPODIUM. For an example illustration see images of a live ABALONE.

FRILLED or FRILLY   Having a wrinkled, fluted, or crumpled edging of laminae, flanges, or blade-like varices; see also: FIMBRIATE.

FRINGED   Having an edging or trimming of projecting ends of sculptural elements; twisted or PLAITED at the margin.

FROND   A FOLIACEOUS, leaf-like extension of a sculptural element, as on a vertical spine; see also: FOLIATION.

FRONDOSE   Resembling a much divided leaf, like a palm leaf; see also: FOLIATION.

FRONT   The surface of a shell on which the aperture appears.

FULGURATE   Like a flash of lightning; said of coloration patterns; see also: FLAMMULE.

FUNICLE   A ridge of callus spiraling into the UMBILICUS in the naticid gastropods; see also: COLUMELLAR FOLD.

FUNICULAR   Pertaining to a cord, shaped like a small cord or band.

FUNNEL   In CEPHALOPODS, the tube on the ventral side of the body used to expel water from the mantle cavity. See also: MULLERS ORGAN.

See illustration of composite squid by Young, Vecchione, and Mangold.

FUNNEL PLATES   Transverse LAMINAE in wall of radiolitid lower valve, inclined downward and funnel-wise toward axis and combining with radial laminae to produce cellular structure.


FURROW   A narrow channel, GROOVE, or wrinkle; see also: SCROBICULATE; SULCATE.

FUSED   United or bound together; merged into a single structure or surface.

FUSIFORM   Spindle-shaped; biconic, i.e., swelling in the central part and tapering at the extremities.
See other gastropod shapes.

FUSION   Something formed by merging; the process of merging.

FUSION LAYER   Part of LIGAMENT secreted where the MANTLE edges are united dorsally by secondary FUSION (i.e., anteriorly and posteriorly to mantle isthmus).


GAPE   A narrow opening remaining between the VALVES of a bivalve when the ADDUCTOR MUSCLE have closed the shell.

GAPING   Not closing tightly; in bivalves, having the VALVES not meet, so as to leave a hole or GAPE; see: CLOSED.

GARSTANG'S THEORY   [need definition]; see also: TORSION.

GASTRIC SHIELD   A flange of protective cuticle of the stomach wall on which the head of the rotating STYLE bears upon or is partly surrounded by.

GASTROPOD   A UNIVALVE, a SNAIL, a member of the class Gastropoda; see also: CONCH, PERIWINKLE, etc.

GASTROPODNET LISTSERV   A mailing list on a LISTSERV which is hosted by Georgia State University (GSU) for "researchers using molluscs as model systems".

See the compilation of information about Molluscan Listserves.

GASTROVERM   Common name for a member of the molluscan class Monoplacophora; limpet-shaped, segmented, snail-like molluscs living in very deep water. Living genera include Laevipilina, Monoplacophorus, Neopilina, and Vema.

GELOINA   [need definition].

GEM   A term used to designate the quality of a shell as perfect... no flaws whatsoever; see also: GRADING SYSTEM.


GENITAL PORE   [need definition]; = GENITAL OPENING; See labelled photo on

GENOTYPE   The genetic makup of an organism. The genetic makeup of an organism can distinguish one species from another, as well as document lineage. See also: PHENOTYPE.

(pl. GENERA)
  [need definition]

(abbrev: GEN. NOV.)
  A new GENUS; Used in publication the first time (and first time only!) that a new genus is presented; see also: SPECIES NOVUM.

GEODUCK   A clam of the Pacific Northwest (USA) by the name Panopea generosa Gould, 1850. Pronounced GOO-ee-duck, the clams are farmed and harvested commercially and may live to over 100 years (oldest=168).

See: Discovery Channel episode of "Dirty Jobs" that featured Geoduck farming.

See: Vadopalas, B.; T.W. Pietsch & C.S. Friedman. 2010. The proper name for the geoduck: resurrection of Panopea generosa Gould, 1850, from the synonymy of Panopea abrupta (Conrad, 1849) (Bivalvia: Myoida: Hiatellidae). Malacologia 52(1):169−173.

Photo: Panopea sp.

GERONTIC   Showing the characteristics of old age, and/or abnormally extreme SIZE.

GIANT CLAM   A CLAM of family Tridacnidae, genus Tridacna.

GIANT SQUID   SQUID, often of extremely large size, typically members of the CEPHALOPOD genera Architeuthis and Ommastrephes.
Photo: Ommastrephes caroli (with a meter stick in the photo, for reference)

GIBBOSE (or GIBBOUS)   Swollen.


GILL RETRACTOR MUSCLE   Muscle present in a few bivalvia, attaching one of the GILLS to the shell.

GIRDLE   A flexible, leathery, muscular integument holding the CHITON valves in place, often ornamented with BRISTLES, SCALES, SPICULES, GRANULES or hairy processes. See illustration: Composite Chiton.

GIZZARD PLATES   [need definition].

GLABROUS   Smooth.

GLADIUS   The "PEN" or internal remnant of a shell, in some CEPHALOPODS, e.g. SQUID.

See the detailed web page on gladius terminology, from the excellent "Cephalopod Glossary" by Richard E. Young, Michael Vecchione, and Katharina M. Mangold.

GLAND   A body organ producing one or more specific chemical substances.

GLASS SCALLOP   Common Name for CLAMS (bivalves) of the family Propeamussiidae; See also: SCALLOP. See Henk Dijkstra's website on Scallops.

GLAZED   Having a shiny surface or shiny deposit; see also: MARGARITACEOUS; NACREOUS.

GLOBOSE   Roughly spherical in form; rounded; see also: GLOBULAR; NERITIFORM. See other gastropod shapes.

GLOBULAR   Globe-shaped or sphere-shaped, like a ball; see also: GLOBOSE.

  The LARVAE of freshwater Unionacean bivalves. As a dispersal mechanism, this larva temporarily attaches itself to the gills of fish.

GONAD   The sex gland in which the sperm or eggs are formed.

GOOD   A term used to designate the quality of a shell as deficient in one character, as color, otherwise "FINE;" see also: GRADING SYSTEM.

GRADING SYSTEM   Degrees of condition of specimens, usually employed by shell dealers.
GEM:  perfect
FINE+:  very slightly irregular
FINE:  minor breaks or scars
GOOD:  deficient in one character
FAIR:  with either major break or poor color
POOR:  badly beachworn; having major breaks


GRANULATED   Having a rough surface of grain-like elevations; see also: GRANULOSE.

GRANULE   A pustular surface sculpture. In CHITONS, these may adorn the GIRDLE. See illustration: Composite Chiton. See also: PUSTULE.

GRANULOSE   Grainy or finely pustulose; covered with granules; see also: GRANULATED.

GROOVE   A distinct furrow, depression, channel, or hollow cut occurring on the surface as opposed to a thin, shallow scratch (e.g., a STRIA); see also: FISSURE; SCROBICULATE; SULCATE; SPIRAL GROOVE.
Photo by Marlo F. Krisberg; Nerita fulgurans Gmelin, 1791.

GROWING EDGE   The outermost edge of the outer APERTURAL LIP of a gastropod shell, or the margin of a bivalve shell.

GROWTH LINE   A line on the shell surface indicating the position of the shell margin at an earlier stage of growth; = INCREMENTAL LINE; = CONCENTRIC LINE. See illustration: Composite Gastropod and Composite Bivalve. See also: COLLABRAL LINES.

GROWTH RING   Concentric rings of shell material evident as a result of differential growth. These rings may be seasonal, and thereby used to determine the age of the specimen. See: SCLEROCHRONOLOGY.

GROWTH RUGA   Irregular wrinkle on surface of shell, of similar origin to growth line, but corresponding to more pronounced hiatus in growth; see also: RUGA.

GROWTH THREAD   Thread-like elevation of surface of shell, of similar origin to growth line.

GROWTH, EXPONENTIAL   Rapidly, but regularly increasing in size.

GRYPHAEATE   Shaped like shell of Gryphaea (Bivalvia), i.e., with left VALVE strongly CONVEX and its dorsal part incurved, and with RIGHT VALVE flat.

GUTTERED   Marked with wide, shallow GROOVES.

GYROCONIC   Having the WHORLS not in contact with each other; see also: DISCONTIGUOUS; LOOSELY COILED; NAUTILOCONIC.

HABITAT   The kind of place where an organism normally lives. See: AQUATIC; ARBOREAL; ESTUARINE; MARINE; PELAGIC; TERRESTRIAL.

HADAL or HADALPELAGIC   The PELAGIC depth zone greater than 6,000 meters. See also: PELAGIC; EPIPELAGIC (0-200m depth); MESOPELAGIC (200-1000m depth); BATHYPELAGIC (1000-4000m depth; ABYSSOPELAGIC (4000-6000m depth; HADAL (greater than 6,000m depth); NERITIC; BENTHIC; PLANKTONIC.

HAEMOCOEL   [need definition].

HAEMOCYANIN   A copper-containing substance carried in the blood plasma of gastropods and cephalopods, which acts as the respiratory pigment; it colors the blood a faint blue. NOTE: A few gastropods have developed haemoglobin; it is not certain that any bivalve has haemocyanin, but some possess haemoglobin (most do not possess any oxygen-carrying substance, the oxygen partial pressure in the blood being that of the surrounding medium).


HALIOTOID   Ear-shaped, like species of Haliotis; see: AURIFORM.

HAMIFORM   Curved at the extremity; see also: FLEXUOUS; RECURVED; REFLECTED.

HEAD   The ANTERIOR end of an animal.

HEAD SHIELD   The shovel-like configuration (designed for burrowing) of the head of CEPHALASPID gastropods.

HEAD VALVE   The first of (typically) eight valves of a CHITON. See also: TAIL VALVE; MEDIAN VALVE.

See illustration: Composite Chiton.

HEART   [need definition].

  A specially modified ARM of CEPHALOPODS which is used to transfer SPERMATOPHORES from the male to the female.; see also: SPADIX; TENTACLE.

HEIGHT   In bivalves: the greatest distance measured vertically, from the UMBONES to the ventral margin, i.e., dorsoventrally. In gastropods: the distance from the tip of the SPIRE to the most DISTAL point along the AXIS of the shell. See illustration: Composite Gastropod. See also: LENGTH; WIDTH; WRS.

HELICAL   Spirally coiled.

HELICIFORM   Shaped like shells of the genus Helix. See also: ESCARGOT. See other gastropod shapes.


HERMAPHRODITE   Having both sexes in the same animal; see also: AMBISEXUAL; MONECIOUS.

HETERODONT   In certain bivalves, having the hinge differentiated into distinct cardinal and lateral areas. See illustration: Composite Bivalve. See also: ARTICOID TYPE; CORBICULOID TYPE; DENTITION; LUCINOID TYPE.

HETEROMYARIAN   The restriction of the anterior adductor muscle (in bivalves) to a small size, with the moving of the byssus and foot to the anterior (as in the Mytilidae); see also: ANISOMYARIAN; DIMYARIAN; MONOMYARIAN.

HETEROPOD   [need definition]; see also: PTEROPOD.

HETEROSTROPHIC   Having APICAL whorls coiled in a direction apparently opposite to that of succeeding WHORLS; see also: HYPERSTROPHIC.

HETEROSTROPHY   Condition of having the gastrpod PROTOCONCH coiled at 90 degrees to the POSTMETAMORPHIC whorls.


HIBERNATE   To pass the winter in an inactive state; see also: AESTIVATE.


HIGH SPIRED   Said of a gastropod shell which is much higher than wide; see also: LOW SPIRED.
See other gastropod shapes.


HINGE AXIS   Imaginary straight line along which 2 valves of a shell are hinged; = CARDINAL AXIS; see also: HINGE LINE.

HINGE EAR   In bivalves, an anterior and/or posterior expansion of the VALVE in the hinge area; = AURICLE.

HINGE LINE   In bivalves, the region along which the VALVES are attached to each other. Term applied loosely by many authors to part of bivalve shell bordering dorsal margins and occupied by or close to hinge teeth and ligament; used by some in same sense as HINGE AXIS.

HINGE MARGIN   Edge of bivalve shell that approximates most closely to hinge axis.

HINGE PLATE   In bivalves, the dorsal margin carrying the hinge teeth; = CARDINAL PLATFORM. A shelly, internal platform, bearing hinge teeth, situated below the beak and adjacent parts of dorsal margins, and lying in plane parallel to that of the commissure. See illustration: Composite Bivalve.

HINGE TOOTH   Shelly STRUCTURE in bivalves (usually on of a series) adjacent to dorsal margin and received in socket in opposite VALVE; hinge teeth serve to hold valves in position when closed.

HINGE TOOTH SOCKET   The indentation, in a bivalve shell, which accepts the protruding HINGE TOOTH when the valves are closed. See illustration: Composite Bivalve.


HINGE, TRANSPOSED   Condition in which certain hinge teeth present in one valve occupy positions of teeth usually found in the other (= TRANSPOSED HINGE TOOTH). See: Van der Schalie, H. 1936. Transposed hinge teeth of North American naiades. Nautilus 49(3):79-84.


HIRSUTE   Covered with hairs.

HOLLOW SPINE   A stiff, sharp, sculptural structure, the interior of which is not filled with shell matter. see also: HYOTE SPINE.

HOLOHEPATIC   Having the "liver" or digestive gland compact; see also: CERATA; CLADOHEPATIC.

HOLOPLANKTON   PLANKTON which spends its entire life in the water column. See also: MEROOPLANKTON.

HOLOSTOMATE   Characterizing an aperture lip of a gastropod shell that is uninterrupted by any anterior notch or sinus; = HOLOSTOMATOUS; see also: ENTIRE; SIMPLE; SIPHONOSTOMATE (= SIPHONOSTOMATOUS).


HOLOTYPE   A single specimen upon which a species is based; the only specimen unquestionably identifiable as a given species; see also: LECTOTYPE; TYPE SPECIMEN.

See the publication: "Terminology of Types" by Frizzell.

HOMOMYARIAN   Bivalves having two ADDUCTOR MUSCLES equal in size or almost so; = ISOMYARIAN.

HOMONYM   One of two identical names given to separate species (the latter would be termed the JUNIOR SYNONYM, the first, the SENIOR HOMONYM). See also: HOMONYM; HOMONYMY; PRIMARY HOMONYM; SECONDARY HOMONYM.

HOMONYMY   A nomenclatural situation in which two or more different species bear the same name. See also: HOMONYM; SYMONYMY.

HOOK   A SPINE tip that is bent or strongly recurved.

HORNY   [need definition]; see also: CHITINOUS.

HUMPED   Being somewhat higher in the center of the dorsum than towards the anterior or posterior (as in some Cypraea spp.).

HYALINE   Glassy and semi-transparent; see also: PELLUCID.

HYBRID   The offspring of parents of two different populations, and usually two different SPECIES.

HYOTE SPINE   Hollow, tubular, and cylindrical shell outgrowths open distally at their tips as well as on their distal flanks, arising periodically from the thin edges of shell margins of OYSTERS [the tip ends are rounded, ear-shaped openings, typically developed on Hyotissa hyotis (Linne, 1758)].

HYPERSTROPHIC   [need definition]; see: ULTRADEXTRAL; see also: HETEROSTROPHIC.
See other gastropod shapes.

HYPNOMIC SINUS   In cephalopods, the notch in the shell margin for the HYPONOME or excurrent siphon.

HYPOBRANCHIAL   Situated below the gills.

HYPOBRANCHIAL GLAND   Large mucous gland beside the rectum ("hypobranchial" is a misnomer) and which consolidates particles before the leave the pallial cavity.


HYPONOTAL LAMELLAE   Folds, on the underside of a NUDIBRANCH, that contain the branches of the digestive gland.

HYPOPLAX   An accessory, ventral shell piece between the valves in some burrowing clams. Elongate, calcareous ACCESSORY PLATE extending along posterior end of ventral margin in some Pholadidae. MESOPLAX; METAPLAX; SIPHONOPLAX.
Photo: Cyrtopleura costata (Linne, 1758)

HYPOSTRACUM   (1) Inner layer of shell wall, secreted by entire epithelium of MANTLE (original usage of term); (2) part of shell wall secreted at attachments of ADDUCTOR MUSCLES.

HYPOTYPE   A specimen not in the original TYPE MATERIAL of a species but known from a published illustration or description.

See the publication: "Terminology of Types" by Frizzell.

(also: ICZN)
  International Commission on Zoological Nomenclature (convenes in London). Also, the International Code of Zoological Nomenclature, that is maintained by the Commission. An associated publication of interest is the Bulletin of Zoological Nomenclature. See also: ITZN.

(also: ITZN)
  The International Trust for Zoological Nomenclature states its mission as "The International Trust for Zoological Nomenclature (ITZN or “the Trust”) was established in 1947, registered in England as a non profit company limited by guarantee. ITZN acts on behalf of the Commission to raise and administer funds in accordance with the policy of the Commission and the International Union of Biological Sciences (IUBS)." [note: "the Commission" = ICZN]

(abbrev: IBID)
  The same.

ICONOGRAPH   An illustrated systematic treatment; an illustrated MONOGRAPH.

IMBRICATE   Having overlapping scales or laminae; see also: SQUAMOUS.

IMMATURE   Not fully developed; said of shell characters that are partly or completely different from those at maturity.

IMMERSED   Sunken; said especially of APICAL whorls.

IMPERFORATE   Not open or perforated; often said of a closed UMBILICUS; see also: PERFORATE.

IMPRESSED   Indented, as in the case of a line pressed into an otherwise unscored surface; said of a shell SUTURE; see also: ADPRESSED; CHANNELED; SUTURE, IMPRESSED.


(abbrev: IN LITT)
  Information conveyed in literature, e.g., a letter or by other correspondence; see also: PERS. COMM.

INCIPIENT   About to develop or appear; beginning to appear.

INCISED   Sculptured with sharply cut GROOVES.

INCRASSATE   Thick or thickened (e.g., the hinge of Glycimeris spp.); see also: MARGINATE.

INCREMENTAL AXIAL   In gastropods, the GROWTH LINES between lines of AXIAL ribbing.


INCURRENT   Forming passage for current of water drawn into mantle cavity from medium (applied to mantle opening or siphonal opening); = INHALANT; see also: EXCURRENT.

INCURVED   Curved inwardly toward the shell or upward and inward toward the SPIRE; see: INFLECTED.


INDENTATION   A NOTCH or recess in the margin of an APERTURAL LIP, vertical margin, or other surface.

INDENTED   Pressed in or having dents or a series of small cavities.

INDIGENOUS   Occurring naturally in a particular region; not introduced; see also: ENDEMIC.

INDUCTURA   An unusually large and erect expansion of the inner APERTURAL LIP of a gastropod shell; a smooth, shelly layer extending from the inner side of the APERTURE; see also: CALLUS.

INEQUILATERAL   In bivalves, having the parts of the shell anterior and posterior to the beaks differing appreciably in length; see: INEQUIVALVE; SUBEQUILATERAL.

INEQUIVALVE   In bivalves, having one valve that is larger (as in the genera Anadara and Corbula) or more convex (as in the genus Pecten) than the other valve. See also: EQUIVALVE; MARGIN, DISCORDANT.
See other bivalve shapes.
Photo: Anadara brasiliana (Lamarck, 1819)

INFERIOR VALVE   That valve (of "attached" bivalves) which is attached to the substrate; = ATTACHED VALVE; = LOWER VALVE.

INFLATED   Swollen; typically applied to rotund shells of a thin texture; see also: TUMID; TURGID; VENTRICOSE.

INFLATION   The distance, in bivalves, between two planes parallel to the plane of commissure and touching outermost parts of two valves.

INFLECTED   Turned inwards, e.g., the outer lip of a spiral shell when it turns toward the body whorl; see: REFLECTED; INCURVED.

INFRAMARGINAL   Situated below a MARGIN.

INFUNDIBULIFORM   Funnel-shaped, as in the siphon or funnel of a CEPHALOPOD.


INHALANT SIPHON   [need definition]; see also: EXHALANT SIPHON.



INSERTAE SEDIS   Uncertain classification.

INSERTION   In gastropods, the point where the OUTER LIP meets the PARIETAL WALL.

INSERTION PLATE   Narrow marginal extensions of the ARTICULAMENTUM of the valves of CHITONS projecting into the GIRDLE.

INSERTION TEETH   Articulating processes that unite the valves of a chiton to the GIRDLE or INSERTION PLATES.

  The condition in bivalves of having no PALLIAL SINUS; see also: SINOPALLIATE.

INTEGUMENT   An outer covering layer of the soft parts.

INTERBAND   Longitudinal band on surface of lower valve of radiolitid rudist, separating two bands designated as siphonal bands.

INTERCALATE   Interposed; interspersed.

INTERCOSTAL   Of or in the spaces between ribs or COSTAE.

INTERDENTUM   Shelly plate present in some Unionidae bridging space between PSEUDOCARDINAL and LATERAL TEETH.

INTERGRADE   To possess characters (as in a series of specimens) that bridge the morphological gap between one entity and another.

INTERNAL   On the inside; see: EXTERNAL.


INTERNAL SHELL   Having the shell always inside of an animal (as is the shell of Aplysia spp.).

INTERSPACE   Space between regular sculptural features; in particular, channels between sculptural ribs; see also: INTERSTICE.

INTERSTICE   A space between structures; see: INTERSTITIAL.

INTERSTITIAL   Pertaining to or occurring in INTERSTICES.

INTERTIDAL   Located on the shore between low-tide and high-tide levels.

INTERVAL   A space or gap, in many cases between sculptural or color elements; synonymous with INTERSPACE, when applied to ornament.

INTERVARICAL   Lying between two VARICES.

INTERVARICAL SPACE   The area between one VARIX and another; a shell area indicative of active growth.

INTRITICALYX   A chalky, white, surface layer in the shells of many marine molluscan groups. Prominent in the Muricidae, where its patterns of MICROSCULPTURE are often useful in identification.

INTRORSE   Turned inward; turned toward the AXIS.

INVAGINATED   Folded back within itself; see: INVERSIBLE.

INVALID SPECIES   Names not to be used; said of an improper name (those proposed improperly) in TAXONOMY. Do not confuse with validly proposed names which have become NOMINAL SPECIES or SYNONYMS.

INVERSE   Term formerly applied to a chamid bivalve in which attachment is by left valve or a rudist in which attachment is by right valve.

INVERSIBLE   Capable of being withdrawn by being inverted (as in some gastropod tentacles) See also: CONTRACTILE; INVAGINATED.

INVOLUTE   Having the last whorl enveloping earlier ones, so that the height of the APERTURE is generally the height of the shell, as in the Bullidae; see also: CONVOLUTE. See other gastropod shapes.

IRIDESCENT   Reflecting the colors of the rainbow; see also: NACRE; MOTHER OF PEARL.

IRREGULAR   Descriptive of shells which, being attached to or embedded in other marine bodies, have no consistent form due to conforming to the shape of their attachment substrate.

IRREGULARLY COILED   Gastropod coiling in a nonuniform manner, as exemplified by the genus Distorsio; see also: LOOSELY COILED; TIGHTLY COILED; SPIRALLY COILED. See other gastropod shapes.

IRRORATE   Having minute marks of color or minute grains or specs of color, as in Littorina irrorata.

ISODONT   Descriptive of a bivalve shell that has a HINGE with one pair of teeth and one pair of pits on one valve that articulate with two pits and two teeth on the other. See illustration: Composite Bivalve. See also: DENTITION.

ISOMYARIAN   Descriptive of a bivalve shell having two adductor muscle scars on the inner surface which are approximately equal in size; = HOMOMYARIAN.

ISOSTROPHIC   Gastropod COILING coiling in which [need definition].
See other gastropod shapes.

JAW   [need definition].

JUGAL SINUS   In CHITONS, the depression between the sutural laminae; = SUTURAL SINUS; see also: JUGUM.

JUGAL TRACT   In CHITONS, the surface of the TEGMENTUM adjacent to the JUGUM; see also: JUGUM.

JUGUM   A longitudinal ridge, sharp or rounded, on some intermediate CHITON valves. See illustration: Composite Chiton. See also: JUGAL SINUS; JUGAL TRACT.

JUNIOR SYNONYM   A latter name for a SPECIES with an acceptable prior name.

JUVENILE   Demonstrating the characteristics of immaturity, as in shell growth; see also: ADULT.

KEEL   A prominent, sharply raised sculptural element, most frequently spiral in orientation. See illustration: Composite Gastropod.

KEELED   Having a prominent sharp ridge; see also: CARINATE; KEEL.



LABIAL PALPS   [need definition].

LABIAL TOOTH   A CERATUS, a relatively long, spur-like or hornlike extension of the outer lip margin of a gastropod shell, projecting toward the interior of the aperture.

(pl. LABIA)
  The INNER LIP of the APERTURE; see also: PERISTOME.

LABRAL   Pertaining to the outer APERTURAL LIP margin (by common usage; properly: LABIAL).

LABRUM   The OUTER LIP of the aperture; see also: PERISTOME.

  Small gap or pits.

LAMALLA, AXIAL   [need definition]. See illustration: Composite Gastropod.

  A thin plate or scale, generally more or less erect; see also: LAMINA; RUFFLED; SQUAMOUS; WEBBING.

LAMELLAR LAYER   Plate-like; the thick middle layer of a shell; see also: PRISMATIC LAYER; PORCELANEOUS LAYER.


LAMELLIBRANCH   Older name for any BIVALVE having platelike gills.

LAMELLOSE   Having numerous plates or scales on the surface; see also: LAMELLATE.

  A plate or scale, generally parallel to the shell surface.

LAMINAR TOOTH   [need definition]; used in describing Neaeromya (see: Abbott, 1974).

LAMINATE   Formed of thin, overlapping plates or scales.


LANCEOLATE   Shaped like a lance; extended to a point at both ends.

LANGMUIR TROTH   The groove, constructed by the FOOT of gastropods floating upside down on the surface of water, which collects the surface monolayer of protein, draws it over the foot by CILIA, and is intercepted by the RADULA. This process accomplished by the freshwater Lymnaea, and tropical prosobranchs Ampullarius and Pila.

LAPPET   A fold, lobe, or small flap.

(abbrev: LAPSUS)
  An unintentional error in spelling.

(pl. LARVAE)
  The juvenile stage, following the egg, of many forms of life; usually provides a mechanism for dispersal of the species; see also: DORATOPSIS; ECHINOSPIRA; GLOCHIDIUM; LECITHOTROPHIC; NEOTENY; PEDIVELIGER; PLANKTOTROPHIC; PROTOCONCH; RHYNCHOTEUTHIS; SPAT; TROCHOPHORE; VELIGER.

LATERAL   Situated at the side of or arising from the side of a structure (in reference to a shell, RADULAR tooth, etc.).

LATERAL HINGE SYSTEM   Hinge structures present in some PRODISSOCONCHS anterior and posterior to the PROVINCULUM.

LATERAL SECTION   More or less raised area on the TEGMENTUM of valves II to VII of a chiton shell, bounded by the posterior edge of the valve and by a line from the midpoint to the ANTEROLATERAL edge; see also: MEDIAN SECTION; POSTERIOR SECTION.

LATERAL TOOTH   In gastropods, those teeth of a RADULA which lie immediately to the side (left and right) of the RACHIDIAN or central tooth and more inward from the MARGINAL TOOH (if present). See also: RADULA FORMULA.

In bivalves, those shelly protuberances on the dorsal margins of the shell, and at some distance from the UMBONES. In Bivalves, at or of the hinge area on either side of the cardinal area, well removed from the BEAKS.

LATTICED   Having crossed sculptural elements; see also: DECUSSATE; DIVARICATE.

LEADING EDGE   The side or surface of a sculptural structure nearest the line of active growth; TRAILING EDGE.

LECITHOTROPHIC   A type of egg having a large supply of yolk; the LARVA takes no food while in the plankton, and is considered to be a rather clumsy "YOLK LARVA"; see also: PLANKTOTROPHIC.

LECTOPARATYPE   [need definition].

See the publication: "Terminology of Types" by Frizzell.

LECTOTYPE   A specimen selected from primary syntypic material to serve in place of a HOLOTYPE where one either was never selected by the original author or has definitely been lost or destroyed; other specimens in the SYNTYPE lot then become LECTOPARATYPE; see also: TYPE SPECIMEN.


(abbrev: LV)
  Valve of a bivalve lying on left-hand side when shell is placed with anterior end pointing away from observer, and with COMMISSURE vertical, the hinge being uppermost; see also: RIGHT VALVE.

Visit Let's Talk Seashells for how to distinguish between right and left valves.

  An abbreviation for the Latin word, legit, which means: Collected by. To avoid confusion, this term is preferred over COLL. which can mean: collected by, but can also mean: in the collection of. Example on a specimen label: Leg. John Doe See also: LEG.

LENGTH   The distance of a specimen, from anterior extremity to posterior extremity. See illustration: Composite Gastropod. See also: HEIGHT; WIDTH; WRS.

LENTICULAR   Shaped like a lentil or lens; having a narrowly doubly convex form, as in the aperture of certain gastropod shells; see also: DISCOIDAL; PLANISPIRAL. See other gastropod shapes.

LESSEPSIAN   Lessepsian comes from the name of Monsieur de Lesseps, the French engineer who cut the Suez Channel and refers to the phenomena of migration facilitated by humans, e.g., through the Suez Channel. "Lessepsian" does not refer only to molluscs, but also to fish, crustaceans, and all forms of marine life which have undertaken this geographic expansion, made possible only by human intervention.

(pl. LIGS)
  A short, common name for a tree snail of the genus Liguus; see also: LIG POLE.

LIG POLE   A long, sometimes collapsible pole with a cup attached to the distal end. This pole is used to extend one's reach up into the trees to dislodge and collect "LIGS" (tree snails of the genus Liguus) in the terminal cup.

LIGAMENT   A band of tough, brown, elastic material which unites the dorsal margins of a clam, usually posterior to the BEAKS, sometimes externally visible, rarely internal; causes the valves to open when the adductor muscles relax; see also: ALIVINCULAR; AMPHIDETIC; BOURRELET; CARTILAGE; DUPLIVINCULAR; LIGAMENT, FIBROUS; MULTIVINCULAR; PARIVINCULAR; RESILIAL RIDGE. TENSILIUM.

See: Bivalve terminology, Anatomy of bivalves by Marlo Krisberg.

LIGAMENT FULCRUM   Narrow, lunate platform extending posteriorly from beak along dorsal margin and serving for attachment of ligament; = NYMPH.

LIGAMENT GROOVE   Narrow depression in CARDINAL AREA for attachment of fibers of the LIGAMENT.

LIGAMENT PIT   Relatively broad depression in cardinal area for attachment of ligament in bivalves; see also: CHONDROPHORE; COCHLEATE.

LIGAMENT RIDGE   Narrow ridge or lamina formed by projection of outer layer of shell wall into body cavity of many rudists (particularly hippuritids and radiolitids), thought to have served for attachment of ligament.

LIGAMENT STRUCTURE   Elongated space behind UMBONES apparent after erosion of LIGAMENT.

LIGAMENT, EXTERNAL   That part of the ligament visible from outside the bivalve shell, consisting of a LAMELLAR LAYER under tensional stress. See illustration: Composite Bivalve. See also: LIGAMENT, (types).


LIGAMENT, INTERNAL   (1) = RESILIUM; (2) Inner layer of ligament; = FIBROUS LIGAMENT. See also: LIGAMENT, (types).

LIGAMENT, LAMELLAR   Part of ligament characterized by lamellar structure and containing no CALCIUM CARBONATE; secreted at mantle edge and elastic to both compressional and tensional stresses. See also: LIGAMENT, (types).

LIGAMENT, PRIMARY   Part of ligament, of bivalves, representing original condition of structure, consisting of PERIOSTRACUM and lamellar and fibrous layers, but excluding secondary additions, notably FUSION LAYER. See also: LIGAMENT, (types).

LIGAMENTIFEROUS   Having or containing the LIGAMENT, e.g., the CARDINAL PIT of Mya spp.

LIGULATE   Thin, slender, like a slip or neck of any thing (e.g., the muscular impression of Lucina spp.); see: ATTENUATED.

LIMACIFORM   [need definition]; used by Abbott, 1974 (pg. 367) in description of Dendronotus.

LIMPET   A common name for saltwater and freshwater SNAILS (GASTROPODS) which have a low profile, conical (PATELLIFORM) shell.


LINEAR   Resembling a line; long, often narrow, and of uniform breadth; see also: RECTILINEAR.

LINGUIFORM   Tongue-shaped. See also: ELONGATE

LIP   The margin of the aperture; the inner lip (= LABIUM) extends from the foot of the columella to the suture and consists of the columellar lip and the parietal lip. The outer lip (= LABRUM) is that part of the aperture farthest from the axis of coiling; see also: PALATAL; PERISTOME.

LIP, COLUMELLAR   The lower portion of the INNER APERTURAL LIP; see also: LIP, PARIETAL.

LIP, FLARED   [need definition]. In the Strombidae…

LIP, INNER   The portion of the apertural margin of a gastropod shell opposite the outer lip and abutting the earliest portion of the body whorl; = LABIUM; the combination of the COLUMELLAR LIP and the PARIETAL LIP.

LIP, OUTER   The outer, distal, growing or leading edge of a gastropod shell; = LABRUM; = PERISTOME. See illustration: Composite Gastropod. See also: OUTER APERTURAL LIP; PALATAL.

LIP, PARIETAL   The upper portion of the inner APERTURAL LIP, which is attached to the subsequent WHORL.

LIP, REFLECTED   [need definition].

(pl. LIRAE)
  Fine linear elevation on shell surface or within OUTER LIP (Cox, 1960); this feature is often on the inner surface of the outer lip of the APERTURE; see also: STRIA.

LIRATE   Sculptured with spirally oriented RIDGES, as in the APERTURE of a shell; see also: STRIATE; VERMICULATION.

LIRATION   A fine, threadlike spiral sculptural element; see also: LIRA.

LIST SERVE; LISTSERVE; LIST SERVE; LIST SERV; LIST SERVER   These are all misspellings, and perhaps misuse, of the licensed registered trademark LISTSERV®.

See the compilation of information about Molluscan Listserves.

  "LISTSERV"® is a licensed registered trademark for an "opt-in" mailing list system that permits people to send one email which gets distributed automatically to many other people with similar interests. This system was developed in 1986 and licensed/registered by L-Soft. The term has come to be used rather loosely to refer to any such system.

See the compilation of information about Molluscan Listserves.

LITHODESMA   A CALCAREOUS reinforcement of an INTERNAL LIGAMENT; = OSSICLE and OSSICULUM. Characteristic of some genera of the Anomalodesmaceae.

LITTLENECK   The young of the QUOHOG clams, Mercenaria mercenaria. See also: CHERRYSTONE.

LITTORAL   Pertaining to the shore.

LIVE SHELL   Term applied by collectors to a shell which had a live animal in it when collected; see: DEAD SHELL.

LOBATE   Having prominent projecting and rounded divisions (LOBES); see also: BILOBATE; TRILOBATE.

LOBE   A rounded or flap-like projection; see also: BILOBATE; LOBATE; TRILOBATE.

LOBIFORM   Lobe-shaped.


LOGARITHMIC SPIRAL   The kind of spiral exemplified by the shell WHORLS of the chambered nautilus; the kind of spiral formed by the rolling up of a cone, as distinct from one formed by the rolling up of a coil of rope; see also: COILING.

LONGITUDINAL   Direction of the longest diameter; in snails, spoken of as AXIAL (as in axial ribs); in bivalves, the direction parallel to that of the cardinal axis; see also: CONCENTRIC.

See other gastropod shapes.

LOT   One or more specimens of one species from one locality and collected at the same time.


LOW SPIRED   Said of a gastropod shell which is much wider than high; see also: HIGH SPIRED.
See other gastropod shapes.

LOWER VALVE   In attached bivalves, the valve which is attached to the substrate; = ATTACHED VALVE; = INFERIOR VALVE. See also: UPPER VALVE.

LUCINOID TYPE   Type of HETERODONT dentition in bivalves, with two CARDINAL TEETH in each valve, anterior one in LV occupying median position below BEAKS.

LUMEN   The hollow center of a tube or cylinder.

LUMPER   In taxonomy, one who recognizes fewer species because they believe that differences between two or more species are minor and that they all should be treated as one species. See also: SPLITTER.


LUNATE   Shaped like a moon; see also: SEMILUNATE.

LUNG   A breathing organ of the Pulmonate gastropods; see also: GILL.

LUNULE   A heart-shaped (CORDIFORM), depressed area in front of the BEAKS of a bivalve. See illustration: Composite Bivalve. See also: ESCUTCHEON.

See: Bivalve terminology, Anatomy of bivalves by Marlo Krisberg.

LV   The abbreviation for "LEFT VALVE" of a bivalve shell. See also: RV.

LWC - Little White Clam   LWC is an abbreviation for Little White Clam. The term is typically applied to a multitude of unidentified specimens of small, white bivalves.

LYRATE   Shaped like a lyre.


MACROSMATIC   Being small-dependant, rather than dependant on some other sense or condition.

MACULATED   Spotted or patched, usually referring to coloration.

MACULATION   An arrangement of regular or irregular spots or markings.


MALACOLOGICAL SOCIETY   An organized group of individuals (MALACOLOGISTS) dedicated to MALACOLOGY.
Examples in the United States of America (USA) include: A list of additional and similar organizations is maintained on the Conchologists of America (COA) website. See also: SHELL CLUB.

MALACOLOGIST   A specialist in the study of molluscs (MALACOLOGY), especially one who deals with soft parts as well as shells. See also: CONCHOLOGIST; TEUTHOLOGIST.

MALACOLOGY   The study of both the anatomy (soft parts) and shells of molluscs. The term was introduced as "malacologie" by Rafinesque in 1814, in his "Somiologie," a treatise on the nomenclature and classification of animals and plants. See also: MALACOLOGICAL SOCIETY; CONCHOLOGY; MALACOLOGIST; TEUTHOLOGY.

MALLEATE   Having a minutely hammered or beaten appearance.

MAMMILLATE   Having nipple-like structures; see also: PAPILLATE; PUSTULATE.

MANTLE   The fleshy outer layer of a molluscan body that secretes the shell. The mantle edge may be folded or otherwise modified to form a SIPHON or other structure. See also: EPIPODIUM.

MANTLE CAVITY   A space or chamber formed where the MANTLE edge overlaps the VISCERAL MASS, housing the GILLS (or LUNG) and the outlets of most body systems.

MANTLE EDGE   The portion of the MANTLE that contains the shell-secreting cells; = MANTLE SKIRT.




MARGIN   The free edge, generally of a sculptural element; the edge of the aperture. See: CARDINAL MARGIN; MARGIN, DISCORDANT.

MARGIN, DISCORDANT   With margins of closed valves not in exact juxtaposition, but one overlapping the other; example: Anadara; see also: INEQUIVALVE.

MARGINAL   Located on the margin, or near the edge; see also: TOOTH, MARGINAL"/a>.

MARGINAL CARINA   Ridge in Trigoniacea (Bivalvia) that runs from UMBO to posteroventral angle of shell and delimits posterior area.

MARGINAL TOOTH   Those teeth of a RADULA, which lie to the outside of the LATERAL TEETH; see also: RACHIDIAN; RADULA FORMULA.

MARGINATE   Having an edge or border thicker than the rest of the shell (as in the genus Marginella); see also: EMARGINATE; INCRASSATE.

MARICULTURE   The farming of organisms (e.g., OYSTERS) or plants in an estuarine or salt water environment. The term is used as a restricted subset of AQUACULTURE.

MARINE   Pertaining to or living in salt water; sometimes restrictively used to refer to salt water of approximately 35 parts per thousand salinity; = OCEANIC. See also: AQUATIC; ARBOREAL; ESTUARINE; PELAGIC; TERRESTRIAL.

MATTE   Lusterless; dull surface texture.

MEDIAL   Occurring in the middle.

MEDIAN   Central; a central line or axis.

MEDIAN SECTION   Triangular area of the TEGMENTUM of valves II to VII of a CHITON shell, bounded by the anterior edge of the shell and by the lateral sections; see also: LATERAL SECTION; POSTERIOR SECTION.

  The 2nd through 7th of (typically) eight valves of a CHITON. See also: TAIL VALVE; HEAD VALVE

See illustration: Composite Chiton.

MEGALAESTHETES   Large sensory epidermal PAPILLAE in the Gastropoda and Polyplacophora; see: AESTHETES; MICRAESTHETES.

MELANISTIC   A black or nearly black color form of a species; see also: ALBINISTIC.

MENTUM   A shelf-like projection, in pyramidellids, which lies ventral to the opening of the proboscis sac, between it and the front edge of the foot (its importance is unknown).

MERISTIC   Having bilateral or longitudinal symmetry of parts ; having regular, equal segmentation.

MEROPLANKTON   PLANKTON which spends only a portion of its life in the water column. See also: HOLOPLANKTON.

MESOCONCH   Part of the DISSOCONCH formed at an intermediate stage of growth and separated from earlier and later formed parts by pronounced discontinuities; see also: NEPIOCONCH; PRODISSOCONCH.

MESOGASTROPOD   [need definition].

MESOPELAGIC   The PELAGIC depth zone 200 to 1,000 meters. See also: PELAGIC; EPIPELAGIC (0-200m depth); BATHYPELAGIC (1000-4000m depth; ABYSSOPELAGIC (4000-6000m depth; HADAL (greater than 6,000m depth); NERITIC; OCEANIC; BENTHIC; PLANKTONIC.

MESOPLAX   One of the ACCESSORY PLATES in the Pholadacea, that straddles the two valves at the beaks; a transversely elongated accessory plate lying athwart the umbonal region in some Pholadidae; see also: CALLUM; HYPOPLAX; METAPLAX; SIPHONOPLAX.
Photo: Martesia striata (Linne, 1758)

MESOPODIUM   That part of the FOOT which forms the sole on which the gastropod mollusc creeps; see also: PROPODIUM.

MESOSTRACUM   [need definition]; (refers to some aspect of CHITONS)


METAPLAX   One of the ACCESSORY PLATES in the Pholadacea. Long, narrow plate covering the gap between posterodorsal margins in some Pholadidae; see also: HYPOPLAX; MESOPLAX; SIPHONOPLAX.

METAPOSIUM   Middle section.

MICRAESTHETES   Small sensory epidermal PAPILLAE in the Gastropoda and Polyplacophora; see: AESTHETES; MEGALESTHETES.

MICRO   A size classification of shells used to depict those that are microscopic or requiring a microscope to fully examine. This term may sometimes be used as a display category in SHELL SHOWS, although requiring a microscope to judge the show is not done. One is more likely to see the display category: MINIATURE or simply MINI. See also: GRADING SYSTEM.

MICROSCOPIC   Requiring a microscopic to examine; see also: SUBMICROSCOPIC. See also, size classifications for shell shows: MICRO and MINI.


(abbrev: MINI)
  A size classification of shells, often used as a display category in SHELL SHOWS, to describe shells 6 mm or less in size as a mature or adult shell. See also: MICRO; GRADING SYSTEM.

mm   An abbreviation for millimeter, a unit of measure equal to 0.03937 of an inch; there are 25.4 mm in one inch and 10 mm to one centimeter (cm).

MODIOLIFORM   Shaped like the shell of Modiolus spp.; differing from MYTILIFORM in that the BEAKS are not quite terminal and ANTEROVENTRAL region forms slight bulge.

MOLLUSC   A member of the invertebrate phylum Mollusca. The taxon Mollusca was first used by Johstonus in 1650 to replace the name Mollia (a taxon name used by Pliny for the Cephalopoda). The Phylum Mollusca includes the classes: Gastropoda (gastropods/snails), Rostroconchia (Paleozoic bivalves), Bivalvia (Recent and fossil bivalves/clams), Cephalopoda (squid, octopus, cuttlefish), Polyplacophora (chitons/coat of mail shells), Scaphopoda (tusk shells or tooth shells), Aplacophora (Chaetoderms & Solenogasters) and Monoplacophora (Gastroverms).

MOLLUSCAlist LISTSERVE   A mailing list (not technically a LISTSERV) which is supported by the University of California, Berkeley. Members subscribe to "the list" to facilitate an easy exchange of emails via "posting" one email to "the list" which is distributed by the application to all subscribers of the list to which the initial email was sent.

See the compilation of information about Molluscan Listserves.

MOLLUSCICIDE   A chemical used to kill molluscs, typically used to kill SLUGS and other garden snails that have become pests.

MONECIOUS   Having the male and female sexes in the same animal; see also: DIOECIOUS, AMBISEXUAL; PROTANDRY; HERMAPHRODITE.

MONILIFORM   Composed of a row of beads, like a necklace; see also: BEADED.

MONOGRAPH   An advanced and comprehensive treatment of a family or a group of species or genera; see also: ICONOGRAPH.

MONOMYARIAN   Having only one adductor muscle, the posterior, usually lying in the center of the valves (Ostrea and Pecten are examples); see also: DIMYARIAN; ANISOMYARIAN; HETEROMYARIAN.

MONOPECTINATE   Having one set of comb-like filaments; see also: BIPECTINATE; PECTINATE.


MONOPLACOPHORAN   [need definition].

MONOTOCARDIAN   Having a heart with only one auricle, as a mollusc of the order Pectinibranchia. See also: DIOTOCARDIAN.

MONOTYPE   The type species of a genus so designated by virtue of being the only species originally associated with the genus.

See the publication: "Terminology of Types" by Frizzell.

MOON SNAIL   A SNAIL (GASTROPOD) of the genus Polinices. See also: SAND COLLAR.

MORPHOLOGY   Structure or form; the study of physical structure.


MOUTH   The APERTURE of the shell of gastropods; the opening through which the radula is exposed to obtain and pass food inward to the esophagus.

MS   Abbreviation for manuscript, an unpublished work.

MUCOCILIARY FEEDING   A feeding method consisting of exuding a MUCUS net into which food adheres and is subsequently pulled in and consumed. This is employed by sedentary organisms such as Crepidula spp. See also: CILIA; CILIATED

MUCRO (1)   The posterior, pointed septum of caecid gastropods ( = APICAL PLUG).
Photo: Meioceras cornucopiae

MUCRO (2)   The high point on the eighth (VIII) VALVE of a CHITON shell. See illustration: Composite Chiton.

MUCRONATE   Sharp; see also: MURICATED.

(adj. MUCOUS)
  A sticky, slimy, watery secretion; see also: MUCOCILIARY FEEDING

MULLERS ORGAN   In CEPHALOPODS, glandular tissue in the funnel. See also: FUNNEL.

MULTICOLORED   Composed of many different colors; see also: BICOLORED; STRIGATE VARIEGATED.

MULTILOCULAR   Many chambered; see also: LOCULAR; UNILOCULAR.


MULTISPIRAL   Consisting of whorls of uniform width, as in the OPERCULUM of Batillaria spp.; = OPERCULUM, ANNULATE. See also: PAUCISPIRAL; CONCENTRIC.

MULTIVINCULAR   Type of bivalve LIGAMENT consisting of serially repeated elements of alivincular type; e.g., Isognomon spp.; see also: ALIVINCULAR; DUPLIVINCULAR.

MURICATED   Having sharp points or prickles; see also: MUCRONATE; SPINOUS.

MUSCLE SCAR   An impression on the interior of a shell marking the former place of attachment of a muscle; see also: ACCESSORY MUSCLE; DIMYARIAN; HETEROMYARIAN; MONOMYARIAN; CICATRIX.

See illustration: Composite Bivalve.
See also: Bivalve terminology, Anatomy of bivalves by Marlo Krisberg.

MUSCLE SCAR, ADDUCTOR   The imprint, on the interior of a bivalve shell, created by the attachment of the ADDUCTOR MUSCLE. See illustration: Composite Bivalve.

See: Bivalve terminology, Anatomy of bivalves by Marlo Krisberg.

MUSCLE SCAR, CRUCIFORM   [need definition].

MUSCLE SCAR, PEDAL RETRACTOR   The imprint, on the interior of a bivalve shell, created by the attachment of the PEDAL RETRACTOR MUSCLE. See illustration: Composite Bivalve.

MUSCULAR IMPRESSION   Lines on the interior of shells, generated by the attachment of muscles; e.g., ADDUCTOR SCAR; PALLIAL LINE.

MUSSEL   Bivalves, typically the edible species, of the family Mytilidae. Do not confuse with MUSCLE. See also: BLUE MUSSEL; DATE MUSSEL.


MYOSTRACUM   Part of shell wall secreted at attachments of ADDUCTOR MUSCLES (of bivalves); see also: HYPOSTRACUM.

MYTILIFORM   Shaped like the shell of the genus Mytilus. See other bivalve shapes.
Photo: Modiolus modiolus (Linne, 1758)

NACRE   Iridescent layer of shell, sometimes called "MOTHER OF PEARL." A form of shell structure consisting of thin leaves of ARAGONITE lying parallel to the inner surface of the shell and exhibiting a characteristic luster; see also: DECORTICATED; IRIDESCENT; HYPOSTRACUM; ORTHOGONAL.


NAIAD   Common name for freshwater BIVALVES of the family Unionidae.

NATES   Old name for UMBONES.


NAUTILOID   Having the shape of a Nautilus; see also: PAPER NAUTILUS.

NEBULOUS   Vague, not clearly defined.

NECK   [need definition]. See illustration: Composite Gastropod.

NEOTENY   The attainment of sexual maturity in the LARVAL stage; see also: PAEDOMORPHOSIS.

NEPIOCONCH   Earliest formed part of dissoconch, when separated from later part by pronounced discontinuity; see also: MESOCONCH; DISSOCONCH; PRODISSOCONCH.

NEPIONIC   In the earliest postlarval stage. See also: METAMORPHOSIS; POSTMETAMORPHIC.

NERITE   Common name for members of the GASTROPOD family Neritidae.

NERITIC   That part of the open sea PELAGIC zone over the continental shelf, vs the OCEANIC zone beyond the continental shelf. See also: EPIPELAGIC (0-200m depth); MESOPELAGIC (200-1000m depth); BATHYPELAGIC (1000-4000m depth; ABYSSOPELAGIC (4000-6000m depth; HADAL (greater than 6,000m depth); BENTHIC; PLANKTONIC.

NERITIFORM   A GLOBOSE GASTROPOD shape resembling that of a Nerite snail (e.g., Nerita spp.; Neritina spp.): with few subglobose and rapidly enlarging whorls with a very reduced SPIRE. See other gastropod shapes.

NESTLER   One of the various small mollusks, mostly bivalves, that enter crevices and cavities as larvae and remain there throughout adult life; see also: SEDENTARY; SESSILE.

NEW NAME   A replacement name (NOMEN NOVUM) for a species having a preoccupied previous name (NOMEN NUDUM) or one that is otherwise invalid.

NEW SPECIES   A previously undescribed SPECIES; = SPECIES NOVUM.

NIDAMENTAL GLAND   Organ which secretes the covering for the eggs. See also: CHALAZA.

NODE   A knot, protuberance, or knob; see also: NODULE.

NODOSE   Having numerous protuberances or knobs; PUSTULOSE; see also: NODULOSE.

NODULE   A small NODE. See illustration: Composite Gastropod and Composite Bivalve.

NODULOSE   Having small, rounded protuberances (i.e., NODULES).
Photo: Cerithiopsis greeni (C.B. Adams, 1839)

NOMEN CONSERVANDUM   [need definition].

  A name of doubtful validity for nomenclatural purposes, according to the rules of the ICZN.


  A name published without sufficient documentation to validate it under the International Code (ICZN); such a name may be used later if given with a proper description.

  A "forgotten name" or senior synonym that has remained unnoticed in the literature for more than fifty years. This category was defined by the ICZN in 1958. Opposed by many systematists, it was, in December 1970, repealed by the ICZN in declaration 43.


NOMINAL SPECIES   Any named SPECIES, regardless of the validity of the name. Nominal species names may become SYNONYMS of accepted species names.

NOMINATE   Said of a subordinate taxon that bears the same name and therefore contains the type species of a subdivided higher taxon; e.g., Conus, s.s., is the nominate subgenus of the genus Conus. Buccinidae is the nominate family of the superfamily Buccinacea.

NONBINOMIAL   A name not conforming to accepted principles of BINARY NOMENCLATURE as set forth in the International Code of Zoological Nomenclature (ICZN).

NORMAL   Term formerly applied to chamid bivalves in which attachment is by right valve or to rudist bivalves in which attachment is by the left valve.

NOTCH   An indentation on the margin of a structure; see also: EMARGINATE; STROMBOID NOTCH; TURRID NOTCH.

NOTUM   The DORSAL surface in certain OPISTHOBRANCHS.

NUCLEAR   Pertaining to the PROTOCONCH, or to the larval shell.

NUCLEAR WHORL   The early larval shell, sometimes distinguished from the PROTOCONCH. See illustration: Composite Gastropod. See also: ADULT WHORLS; VELICONCH.

NUCLEUS   The first part or beginning of a SHELL or OPERCULUM; see also: NUCLEAR WHORL; PROTOCONCH.

NUCULANIFORM   A shape exemplified by the bivalve genus Nuculana; = ROSTRATE. See other bivalve shapes.

NUDIBRANCH   [need definition]. See also: ASCOGLOSSAN; SEA SLUG.

NURSE EGGS   Eggs which are placed in the same EGG CAPSULE as other, viable EGGS, but which do not develop; the nurse eggs simply provide post-hatching nourishment for the viable eggs.

NYMPH   A projection along the bivalve hinge margin to support the EXTERNAL LIGAMENT or to reinforce the normal hinge structure; = LIGAMENT FULCRUM; = NYMPHAL PLATE.


OBCONIC   Approximately cone-shaped; see also: BICONIC; CONICAL. See other gastropod shapes.

OBESE   Fat; corpulent; swollen.

OBLIQUE   Slanting; inclined from the horizontal or vertical.

OBLIQUELY OVATE   An OVATE shape which has been titlted to one side. See other gastropod shapes.

OBLIQUITY   Angle between straight dorsal margin (of bivalves) and line bisecting umbonal angle (in terminology of some authors); angle between dorsal margin and most distant point of ventral margin.

OBLITERATED   Eroded; worn away by attrition; rendered imperceptible.

OBLONG   Longer in one direction than in another, with sides more or less parallel; see also: CYLINDRICAL; TUBULAR.

OBOVATE   Reversed OVATE; having the greatest width above the APERTURE, toward the apex. OVATE, with the narrower end basal. See other gastropod shapes.

OBSCURED   Not readily seen; not easily observable.

OBSOLETE   Weakly marked; indistinct; weak to the point of absence; worn out; see also: CORRODED.

OBTUSE   Not pointed or ACUTE; blunt; having an internal angle of between 90 and 180 degrees.

OCEANIC   That part of the open sea PELAGIC zone beyond the continental shelf, vs the NERITIC zone over the continental shelf. See also: EPIPELAGIC (0-200m depth); MESOPELAGIC (200-1000m depth); BATHYPELAGIC (1000-4000m depth; ABYSSOPELAGIC (4000-6000m depth; HADAL (greater than 6,000m depth); BENTHIC; PLANKTONIC.

OCELLI   The tiny, simple eyes, as in the scallop.

OCTOGONAL   Having eight angles (as in some Dentalium spp.); see also: HEXAGONAL; POLYGONAL; QUADRATE; RHOMBOID.

OCTOPUS   A CEPHALOPOD of the order Octopoda or, more restrictively, a member of the genus Octopus. These organisms have eight arms which ususlly bear rows of round suckers.

For a detailed definition, see Wikipedia.

ODONTOPHORE   The rasping organ of early molluscs; the RADULA lies along the middle of the dorsal surface of the odontophore.

OLFACTORY   Pertaining to the sense of smell; see also: MACROSMATIC.

OLIGOGYROUS   Having the number of turns reduced (as in the OPERCULUM of most MONOTOCARDIANS); see also: POLYGYROUS.

OLIGOPYRENIC   The less common type of sperm, which plays no part in fertilization; it is thought that they degenerate in the receptaculum and nourish the Eupyrenic sperm (perhaps analogous to NURSE EGGS; it has also been shown that the oligopyrenic sperm provide a transport mechanism for the eupyrenic sperm; see also: SPERM; EUPYRENIC.

OMNIVOROUS   Feeding on both vegetable matter (HERBIVOROUS) and animal matter (CARNIVOROUS). See also: DETRITIVOROUS.


ONTOGENY   The successional growth stages of a species. See also: PHYLOGENY.

See Wikipedia for Ernst Haekel's "Recapitulation Theory" that ontogeny recapitulates phylogeny.

OPAQUE   Not transparent or translucent; see also: PELLUCID.

OPERCULAR   Pertaining to the OPERCULUM.

OPERCULAR PEG   An narrow extension of the OPERCULUM.

OPERCULATE   Having an operculum; see also: INOPERCULATE.

  A generally oval, lid-like, CORNEUS or CALCAREOUS structure, situated on the posterior end of the FOOT of many gastropods, that closes off the APERTURE when the animal withdraws into its shell; see also: CONCENTRIC; EPIPHRAGM; MULTISPIRAL; OLIGOGYROUS; PAUCISPIRAL; POLYGYROUS; TRAP DOOR; UNGUICULATE, RIGICLAUDENT, FLEXICLAUDENT.
See the website on opercula: The Humble Operculum
Photo: Triplofusus giganteus (Kiener, 1840)

OPERCULUM, ANNULATE   An OPERCULUM with a central nucleus, or nearly so, with other layers surrounding it in flattened rings. See also: MULTISPIRAL.



For illustrations, see The Humble Operculum website page: Operculum Structures.

OPERCULUM, PAUCISPIRAL   An OPERCULUM having only a few whorls or turns, of rapidly increasing width; = OLIGOGYROUS SPIRAL; MULTISPIRAL.

For illustrations, see The Humble Operculum website page: Operculum Structures.

  A work previously cited.

OPISTHOBRANCH   Marine Mollusks which are characterised by having a single gill behind and to the right of the heart; they also have a reduced or absent shell and always lack an OPERCULUM. Included in this group are the BUBBLE SHELLS, the NUDIBRANCHS, SEA HARES and SEA BUTTERFLIES.

OPISTHOCLINE   Sloping (from lower end) in posterior direction [term applied to HINGE TEETH of bivalves and, in some genera, to body of shell]; opposite of PROSOCLINE.

See photos on the "Let's Talk Seashells" website: Tricky terminology, prosocline and opisthocline.

OPISTHODETIC   Located wholly posterior to beaks, in bivalves [term applied to ligament]; opposite of PROSODETIC>/a>.

OPISTHOGYRATE   In bivalves, having the BEAKS pointing backward or posteriorly; opposite of PROSOGYRATE; see also: ORTHOGYRATE; SPIROGYRATE.

ORAL   Situated about or around the mouth; pertaining to the mouth; see also: ABORAL.

ORBICULAR   Circular and flattish; see also: SUBORBICULAR. See other bivalve shapes.

ORIFICE   An opening; in keyhole LIMPETS (Gastropoda: Fissurellidae), a small opening in the MANTLE CAVITY from the exterior, at and through the shell apex.

ORNAMENTATION   Sculptural elements that form part of the shell morphology; see also: COWL; NODE; PIT; PUNCTATION; PUSTULE; RIDGE; SCULPTURE; SPINE; SNAIL FUR.

ORNAMENTED   Sculpturally embellished; not smooth; see also: ORNAMENTATION

ORTHOCLINE   Perpendicular to HINGE AXIS or almost so [term applied to HINGE TEETH and, in some genera, to body of shell]; = ACLINE.

ORTHOCONE   [need definition]; see also: CYRTOCONE; BREVICONE.

ORTHODONT   Type of HINGE in which direction of HINGE TEETH are parallel to CARDINAL MARGIN or almost so.

ORTHOGONAL   Referring to two shell layers that are at right angles to each other. See also: NACRE.

ORTHOGYRATE   In bivalves, having the BEAKS pointing toward each other; see also: OPISTHOGYRATE; SPIROGYRATE.

OSCULE   Orifice in upper valve in some RUDISTS, usually near margin.

OSPHRADIUM   A sensory organ in gastropods in the PALLIAL CAVITY, apparently for the reception of chemical stimuli.

OSSICLE   A small, CALCAREOUS plate reinforcing the INTERNAL LIGAMENT in some bivalve genera; = LITHODESMA; = OSSICULUM.


OSTRACUM   Outer part of CALCAREOUS wall of shell, secreted at mantle edge [original usage]; entire calcareous wall of shell [usage by some later authors]; see also: PERIOSTRACUM.


OUTER LIP   [need definition].

OUTER LIP TOOTH   [need definition]. See: LABIAL TOOTH. See illustration: Composite Gastropod.

OVAL   Like a circle that has been somewhat flattened; see also: OVATE; SUBOVAL.
See other bivalve shapes.

OVATE   Egg-shaped, with the basal end broader; see also: OBLIQUELY OVATE; OBOVATE. See other gastropod shapes.
Photo: Granulina ovuliformis (Orbigny, 1841)

OVERLAPPING   Lying at least partially one over another, as with sculptural elements such as LAMINAE, scales, or plates.

OVERRIDE   To pass over without interruption (e.g., COMMARGINAL elements over radial elements of ornament).

OVIDUCT   [need definition].

OVIPAROUS   Producing young via production of eggs; see also: VIVIPAROUS.

OYSTER   BIVALVED clams of the families Ostreidae (edible oysters), Pteriidae (PEARL oysters), Isognomonidae (tree oysters) and Hyriidae (freshwater oysters). See also: BRANCHITELLUM.

PACHYODONT   Descriptive of a bivalve shell with one heavy, blunt and shapeless hinge tooth; see also: DENTITION.

PAEDOMORPHOSIS   The principle by Garstang, which promotes "escape from specialization" by attainment of sexual maturity in a larval condition. This has brought much-needed support to the annelid theory of molluscan ancestors. It would make the molluscs neotenic annelids that had lost their segmentation by dropping off the original adult stages from their life history. The TROCHOPHORE larva thus becomes the last point of contact between the two phyla; see also: PHLEBOEDESIS. See also: NEOTENY.

PALATAL   Pertaining to the OUTER LIP of a spiral gastropod shell.

PALATAL TOOTH   [need definition].

PALLET   One of the two simple or compound CALCAREOUS structures at the siphonal end of some wood-boring mollusks (such as SHIPWORMS), closing the burrow when the siphons are withdrawn.
Illustration: Teredo sp. (left = entire animal; center = pallets; right = shell)

PALLIAL   Pertaining to the MANTLE, or the region of the GILLS.

PALLIAL CAVITY   [need definition].

PALLIAL LINE   On the inside of some bivalve shells, a linear scar marking the attachment of the margin of the fleshy MANTLE to the shell. See illustration: Composite Bivalve. See also: INTEGROPALLIATE; MUSCULAR IMPRESSION; SINUPALLIATE.

See: Bivalve terminology, Anatomy of bivalves by Marlo Krisberg.

PALLIAL REGION   Marginal region of shell interior adjacent to PALLIAL LINE.

PALLIAL RETRACTOR MUSCLE   Muscle withdrawing marginal parts of MANTLE within bivalve shell where there is no distinct line of muscle attachment.

PALLIAL SINUS   A notch or EMBAYMENT in the PALLIAL LINE caused by the attachment of the siphon's retractile muscles. It may be deep, shallow, or absent... depending on the species. See illustration: Composite Bivalve. See also: INTEGROPALLIATE; SINUPALLIATE.

See: Bivalve terminology, Anatomy of bivalves by Marlo Krisberg.

PALMATE   Shaped like an open palm; like a hand with the fingers extended.

PALP PROBOSCIDES   The prolonged, grooved tentacles of the LABIAL PALPS of bivalves.

PANTODONT   Dentition having the LATERAL TEETH exceeding 2 in any one group; see also: DENTITION.

PAPER NAUTILUS   Common name applied to the external temporary shell constructed by the ARGONAUT to protect its eggs; = PAPER SAILOR. This shell is not made from paper; the shell is "paper thin" (i.e., very fragile) and constructed of calcium carbonate (like most seashells) only by the female of the species and only for purposes of protecting her eggs. Additionally, the Paper Nautilus is not a nautilus at all, but rather is a member of the order Octopoda (which includes the octopusses) and family Argonautidae.
[left photo by Paul S. Mikkelsen, right photo by Carly De Maye] Both photos: Argonauta argo Linne, 1758


  Any small bump or small projection.

PAPILLAE, DORSAL   [need definition]. In NUDIBRANCHS… See illustration: Composite Nudibranch.

PAPILLATE   Nipple-shaped; = PAPPILLOSE.

PAPYRACEOUS   Of a thin, light texture resembling that of paper (often used in reference to the Argonauta).

PARALARVA   In CEPHALOPODS, the first free-living form of the organism, typically found in surface PLANKTON.


PARAPODIA   In sea hares (Gastropoda: Anaspidea), lateral expansions of the FOOT, used for swimming.

PARASITE   [need definition]. See also: COMMENSAL.

PARATYPE   A specimen from the original type material of a species, designated as such to serve as an auxiliary specimen to the holotype; one of a series from primary type material, exclusive of the HOLOTYPE.

See the publication: "Terminology of Types" by Frizzell.

PARIETAL   Pertaining to the region of a gastropod shell that extends from the COLUMELLA posteriorly and around the curve of the shell.

PARIETAL CALLUS   Enamel on the inside of a shell just within the APERTURE of snails; see also: COLUMELLAR CALLUS.

PARIETAL DENTICLE   [need definition]; present in some Polygyridae.

PARIETAL TOOTH   A shelly projection on the PARIETAL WALL of the shell of gastropods. See illustration: Composite Gastropod. See also: PARIETAL.

PARIETAL WALL   In a gastropod, the region just above the columellar region, partly outside and partly inside the aperture; sometimes called the INNER LIP; see also: PARIETAL.

PARIVINCULAR   Longitudinally elongated type of bivalve LIGAMENT, located posterior to beaks and comparable to cylinder split on one side with several edges attached respectively along dorsal margin of two valves; see also: ALIVINCULAR; DUPLIVINCULAR; MULTIVINCULAR.

PARS   In part.

PARTITION   The erect plate of shell matter deposited in some typhine species between the shoulder spine of each varix and the previous whorl, and against which the next spine often rests.

PATELLATE   Saucer-shaped; cap-shaped; shaped like a human knee cap or patella; shell with a low cone, with little or no coiling; = PATELLIFORM.

PATELLIFORM   Shaped like a human knee cap or patella; = PATELLATE. See other gastropod shapes.

PATRONYM   A species (or other) name honoring a specific person.

PAUCISPIRAL   Having only a few WHORLS or turns, of increasing width; see also: MULTISPIRAL; PLANISPIRAL; CONCENTRIC.

PEARL   A CALCAREOUS spheroid secreted by the mantle of a mollusk (mostly bivalves, but some gastropods too), in layers, to reduce the irritation of some foreign particulate matter lodged within the tissues of the animal. The pearl often has a NACREOUS appearance and although predominantly white in color, they may be various colors including blue, pink, green, brown, or nearly black. See also: MARGARITACEOUS; MARGARITIFEROUS; MOTHER OF PEARL.

See: Glossary of Pearl Terms by
See: Glossary of Technical Terms by


PECTINATE   A shape exemplified by the bivalve genus Pecten. see also: BIPECTINATE; MONOPECTINATE.
See other bivalve shapes.

PECTINIFORM   [need definition].
Photo: Argopecten irradians concentricus (Say, 1822)


PEDAL ELEVATOR MUSCLE   Thin bundle of muscle fibers attached to a bivalve shell in the umbonal cavity and serving to raise the foot.

PEDAL GAPE   Opening between margins of shell for protrusion of the FOOT; see also: CALLUM.

PEDAL GLAND   A gland on the gastropod FOOT that secretes a lubricant aiding in locomotion.

PEDAL GROOVE   A longitudinal groove in the body of a snail that marks the boundary where the TUBERCULATE side wall of the foot joins the smooth ventral sole; see also: SUPRAPEDAL GROOVE.

In the neomeniomorph (Solenogastres) APLACOPHORANS, a longitudinal narrow groove which functions as a foot, beginning anteriorly in a PEDAL PIT. See the WHOI website for a photo by Amelie Scheltema.


PEDAL PIT   In APLACOPHORANS, an anterior depression which marks the begining of a PEDAL GROOVE.

PEDAL PROTRACTOR MUSCLE   Muscle present in some bivalve genera, attached to shell interior and serving to extend the foot.

PEDAL RETRACTOR MUSCLE   Muscle attached to shell interior, and serving to retract the FOOT (of bivalves); = PEDAL LEVATOR MUSCLE.


PEDIVELIGER   A VELIGER LARVA which has settled out of the PLANKTON and is in the process of METAMORPHOSIS, resorbing the VELUM, etc., and has the ability to crawl about with the aid of its foot. Term coined by Mel Carriker. See also: PLANTIGRADE.

PEDUNCLE   A stalk or stem-like structure.

PELAGIC   The open sea, made up of the NERITIC zone over the continental shelf and the OCEANIC zone beyond the continental shelf. See also: EPIPELAGIC (0-200m depth); MESOPELAGIC (200-1000m depth); BATHYPELAGIC (1000-4000m depth; ABYSSOPELAGIC (4000-6000m depth; HADAL (greater than 6,000m depth); OCEANIC; BENTHIC; PLANKTONIC.

PELECYPOD   A bivalve, clam, mussel, oyster, scallop, etc. "Pelecypod" is considered an outdated term, and bivalve is usually used to replace it. The term means "hatchet foot." See also: BIVALVE.

PELLUCID   Transparent, limpid; see also: DIAPHANOUS; HYALINE.

PEN   The internal "shell" of SQUID; see also: GLADIUS; RACHIS; VANE.


PENULTIMATE   Next to the last; see also: PENULTIMATE WHORL.

PENULTIMATE WHORL   The next to the last WHORL, or the one before the BODY WHORL (of snails).

PERFOLIATE   [need definition].

PERFORATE   Having a minute opening at the base of the shell; see also: IMPERFORATE; UMBILICATE.

PERFORATION   A round opening, typically having the appearance of being bored.

PERIOSTRACAL GROOVE   [need definition].

PERIOSTRACUM   The outermost molluscan shell layer, composed of CONCHIOLIN; = DRAP MARIN (by French naturalists); erroneously called "epidermis" by authors; see also: OSTRACUM.
Photo: Cymatium pileare (Linne, 1758)

PERIPATETIC   Travelling around to different places. Applies to invasive species and their advance to new areas.

PERIPHERY, ANGULATE   Having the outer whorl midway between CARINATE and ROUNDED.

PERIPHERY, BICARINATE   Having two CARINA or ridges at the outer edge of a whorl.

PERIPHERY, CARINATE   Having one CARINA or ridge at the outer edge of a whorl.

PERIPHERY, ROUND   Having the outer edge of a WHORL smoothly curved.

PERIPHERY, WHORL   [need definition].

PERISTOME   Edge of the aperture on a gastropod shell, including the inner and outer lips. See illustration: Composite Gastropod. See also: HOLOSTOMATE; LABIUM; LABRUM; PERITREME; SIPHONOSTOMATE.

PERISTOME, PERITREME   The margin of the APERTURE; generally said of a margin that is either continuous or interrupted only by the parietal region of the body whorl; see also: HOLOSTOMATE; SIPHONOSTOMATE.

PERITREME   The whole circumference of the aperature of a spiral shell (in descriptions, it is said to be notched or entire, simple, reflected, round or oval, etc.; see also: PERISTOME.

PERIWINKLE   A SNAIL in the family Littorinidae.

PERSISTENT   Lasting; not lost; generally present throughout the development (of a shell); see also: EPHEMERAL.

(abbrev: PERS. COMM.)
  Information conveyed through conversation; see also: IN LITT.


PHARYNX   The throat; the section of the alimentary canal just behind the mouth. See also: ESOPHAGUS

PHENOTYPE   Visually observable characteristics of an organism. Such characteristics are often used to distinguish SPECIES , with LUMPERS and SPLITTERS placing less or more weigh (respectively) on features. The phenotype of an organism can be influenced by the environment. See also: ECOPHENOTYPE; GENOTYPE; XENOMORPHISM.

PHLEBOEDESIS   A process proposed by Lankester, who held that molluscs were derived from segmented annelids that had already acquired a full coelom, in which enlarged blood spaces encroached on the COELOM and reduced it to its molluscan dimensions; see also: PAEDOMORPHOSIS.

PHOTOPHORE   Light-producing organs. These are present in the outer tissues of CEPHALOPODS, and are used by the organism to change colors and patterns.

See the detailed web page on photophore terminology, from the excellent "Cephalopod Glossary" by Richard E. Young, Michael Vecchione, and Katharina M. Mangold.

PHRAGMOCONE   The floatation chambers of a CHAMBERED NAUTILUS or Spirula spirula; See also: CONCAMERATION; SIPHUNCLE.

See the excellent "Cephalopod Glossary" by Richard E. Young, Michael Vecchione, and Katharina M. Mangold.

PHYLOGENOMICS   Phylogenetic studies using dozens to hundreds of genes. See also: PHYLOGENY

See: Kocot, et al. 2011. Phylogenomics reveals deep molluscan relationships. Nature 477:452-456.

PHYLOGENY   The history of the EVOLUTION of various groups or species, usually illustrated with the use of family trees. See also: MONOPHYLY; POLYPHYLY; PARAPHYLY; PHYLOGENOMICS.

See also: ONTOGENY.
See Wikipedia for Ernst Haekel's "Recapitulation Theory" that ontogeny recapitulates phylogeny.

PIDDOCK   The common name for CLAMS a member of the bivalve family Pholadidae, including the genera Barnea, Cyrtopleura, Zirfaea, Martesia and others.

Left photo: Martesia striata (Linne, 1758); Right photo: Cyrtopleura costata (Linne, 1758)

PILLAR   The part of the body whorl of the gastropod shell adjacent to the COLUMELLAR LIP; also, sometimes, the columella. In bivalves, an inward extension of outer shell layer extending longitudinally up the lower valve in HIPPURITIDS; see also: PSEUDOPILLAR.

PILOSE   Covered with hairs, especially with fine and soft hair.

PINNATE   Protuberant and RIBBED; see also: ALATE.

PIT   A small cavity or hole; a pinpoint depression; see also: PUNCTATE; PUNCTUM; QUINCUNX.

PLAIT   A shelf-like fold, generally on the columella of a gastropod shell; see also: COLUMELLAR PLAIT; PLICA; FRINGED.

PLANED   Flat or existing in one plane (e.g., the columellar lip of Purpura spp.).

PLANISPIRAL   Coiled in a single plane; loosely used also with DISCOIDAL shells having asymmetrical sides; see also: MULTISPIRAL; LENTICULAR. See other gastropod shapes.

PLANKTON   Organisms that drift in the water column of salt, brackish, or fresh water. See also: ZOOPLANKTON, HOLOPLANKTON, MEROPLANKTON.

See also: the glossary link on the PlanktonNet website for a large, illustrated glossary of plankton-related terminology.

PLANKTONIC   Floating or suspended in the water column, and generally incapable of overcoming the currents by swimming although some directional movement is possible, usually vertical; see also: BENTHIC; PLANTIGRADE.

PLANKTOTROPHIC   Having a long LARVAL stage (up to 2-3 months) in the PLANKTON, and generally feeding while in the plankton; see also: LECITHOTROPHIC.


PLANORBOID   In gastropods, having the whole coil in the same plane; = PLANORBICULAR; used in reference to ammonites.

PLANTIGRADE (STAGE)   The final, or creeping stage of a gastropod; PEDIVELIGER; VELIGER.

PLATE   A lamina or scale-like structure; see also: HINGE PLATE; SQUAMOUS.

PLATH   A CHITINOUS or CALCAREOUS accessory typical of pholad shells, somewhat flat in shape and held in place by chitinous folds; e.g., PROTOPLAX, MESOPLAX, METAPLAX, HYPOPLAX.

PLEAT   Applied to folds on the COLUMELLA.

PLESIOMORPHY   An ancestral or primitive character. See also: APOMORPHY.

See the Paleos website for greater detail.

PLEURAL AREAS   Side slopes of valves of CHITONS, not including the JUGAL TRACTS.

PLEUROTHETIC   Attached to a substrate; referring to a members of the Bivalvia which settle on to the substrate and attach themselves, often with the attached valve taking on the form of the substrate. See also: ATTACHED; ATTACHED BIVALVE; XENOMORPHISM.

(pl. PLICAE)
  A FOLD; see also: PLAIT; RUGA.

PLICATE   Folded or twisted; having PLICAE.

PLICATIDIUM   Folded, secondary GILL found especially in CEPHALASPID gastropods.


PNEUMOSTOME   A breathing pore. Examples are found arranged in a row in the shells of Abalone (Haliotis spp.).

POLYCHROMIC   Having many colors; see also: POLYCHROMISM.



POLYGYROUS   Composed of many turns (as in the OPERCULUM of DIOTOCARDIANS); see also: OLIGOGYROUS.


POLYMORPHIC   Having many forms; see: POLYMORPHISM

POLYMORPHISM   A circumstance in a group of organisms in which both the close affinities of a species and other, divergent details of morphology are present; see also: DIMORPHISM; POLYCHROMISM.


POLYPLACOPHORAN   Shells of the molluscan class Polyplacophora, commonly called a CHITON or COAT OF MAIL SHELL.

POOR   A term used to designate the quality of a shell as being in bad condition, badly beachworn, and/or with major breaks; see also: GRADING SYSTEM.

PORCELANEOUS   Polished; similar in color and texture to porcelain ceramic. See also: NACREOUS; VITREOUS.

PORCELANEOUS LAYER   The thick, innermost layer of a shell; see also: PRISMATIC LAYER; LAMELLAR LAYER.

POSTERIOR   Toward the apical end of, in coiled gastropod shells, or the siphonal end of, in bivalves; opposite of ANTERIOR; see also: OPISTHODETIC; for bivalves, see also: MARGINAL CARINA; CORSELET.

POSTERIOR CANAL   = ANAL SULCUS; = ANAL CANAL. See illustration: Composite Gastropod. See also: ANTERIOR CANAL.

POSTERIOR LATERAL TOOTH   LATERAL TOOTH situated posteriorly to beaks and (in heterodonts) posterior to the LIGAMENT.

POSTERIOR RIDGE   A ridge, in bivalves, passing over or originating near the umbo and running diagonally towards the posteroventral part of the valve; see also: CORSELET.

POSTERIOR SLOPE   Sector of surface of valve (of bivalves) running posteroventrally from UMBO; see also: CORSELET.


POSTERODORSAL MARGIN   In bivalves, the margin of the DORSAL part of the shell POSTERIOR to the BEAKS.

POSTEROVENTRAL   Being both rearward and downward; toward the rear and lower regions; see also: ANTEROVENTRAL.

POSTEROVENTRAL MARGIN   In bivalves, the posterior end of the valve margin opposite the hinge; = POSTEROBASAL MARGIN. See also: ANTEROVENTRAL MARGIN;



POSTNUCLEAR   Succeeding the nucleus or PROTOCONCH in the growth of a gastropod shell.

POSTNUCLEAR WHORL   Any turn of a GASTROPOD shell formed after the formation of the NUCLEUS.

PRECEDING WHORL   The turn of a GASTROPOD shell just previous to the one being described.


PREOCCUPIED NAME   A taxonomic species name that has been used by a previous author for a different species in the same genus and is therefore unavailable for the present species.

PRICKLE   A small, pointed protuberance.

PRIMARY   Of the first order; most dominant or conspicuous; see also: SECONDARY; TERTIARY; QUARTERNARY.

PRIMARY HOMONYM   A name that is identical to another name. The oldest has priority and is termed the senior primary homonym with the younger name being the junior primary homonym. See also: HOMONYM; SECONDARY HOMONYM; HOMONYMY.

PRIONODONT   Type of hinge in which the teeth are developed in direction transverse to cardinal margin; virtually same as TAXODONT; see also: DENTITION.


PRISMATIC LAYER   The thick outer layer of a shell; see also: PRISMATIC; LAMELLAR LAYER; PORCELANEOUS LAYER.

PROBOSCIS   In GASTROPODS, a tube-like anterior organ bearing the mouthparts at its tip.

PROBOSCIS COLUMN   [need definition].

PROCESS   A sculptural structure projecting from the main body of a shell; see also: PUSTULE.

PRODISSOCONCH   A shell secreted by the LARVA or embryo and preserved at the BEAK of some adult bivalve shells or scaphopod shells; identical with VELICONCH when larva is PELAGIC. See illustration: Composite Bivalve. See also: DISSOCONCH; MESOCONCH; NEPIOCONCH; PRODISSOCONCH I; PRODISSOCONCH II; PROTOCONCH; VELICONCH.

PRODISSOCONCH I   Earlier-formed part of prodissoconch, secreted by the SHELL GLAND of the LARVA; = PRODISSOCONCH; PROTOSTRACUM; PRODISSOCONCH II.

PRODISSOCONCH II   Later-formed part of PRODISSOCONCH, secreted by the MANTLE edge; see also: PRODISSOCONCH I.

PRODUCED   Drawn out; elongate; see also: PROTUBERANT.

  A slit across the anterior margin of the foot of gastropods which coincides with the boundary between the anterior part of the FOOT and the MESOPODIUM; see also: MESOPODIUM.

PROSOCLINE   Sloping (from lower end) in anterior direction (term applied to HINGE TEETH and, in some genera, to body of shell); opposite of OPISTHOCLINE.

See photos on the "Let's Talk Seashells" website: Tricky terminology, prosocline and opisthocline.


PROSODETIC   Located anterior to the BEAKS, in bivalves; opposite of OPISTHODETIC.

PROSOGYRATE   In bivalve shells, curved so that the BEAKS point anteriorly; opposite of OPISTHOGYRATE or OPISTHODETIC; same as PROSOCOELOUS.

PROSOPON   Term recently proposed as suggested improvement on SURFACE ORNAMENT or SCULPTURE.

  Beginning life as a male, passing through an HERMAPHRODITIC (male & female combined) stage, and finishing life as a pure female. This occurs in the slipper limpet, Crepidula fornicata, as discovered by Orton, 1909; see also: RHYTHMICAL SEXUALITY.

PROTOBRANCH   [need definition].

PROTOCONCH   The LARVAL shell, formed by all the nuclear whorls, of a gastropod shell; sometimes this includes (and sometimes excludes) the earlier NUCLEAR WHORLS. See illustration: Composite Gastropod. See also: DISSOCONCH; PRODISSOCONCH; SCAPHOCONCHA; TELEOCONCH; VELICONCH; = NUCLEUS.
See Marlo Krisberg's graphic Counting Protoconch Whorls.

Photo: Acteocina atrata Mikkelsen and Mikkelsen, 1984

PROTOPLAX   One of the ACCESSORY PLATES in the Pholadacea; flat, spearhead-like accessory plate in one piece or divided longitudinally into two, situated at the anterior end of the dorsal margin in some pholadidae. see also: HYPOPLAX; MESOPLAX; METAPLAX; SIPHONOPLAX.


PROTOSTYLE   A stiff mucous rod projecting into the stomach from the intestine which is continuously rotated by cilia and functions in drawing the food in from the esophagus; this is the forerunner of the molluscan CRYSTALLINE STYLE; see also: GASTRIC SHIELD; STYLE SAC.

PROTUBERANT   Bulging beyond the surrounding or adjacent surface; see also: PRODUCED; opposite of RECESSED.

PROVINCE   A portion of the earth in which there exists a more or less distinct faunal or floral assemblage. This assemblage may be limited from extending its boundaries by either physical or environmental barriers, or both. As some physical barriers are not entirely impassible for some species, the boundaries may not appear as distinct lines, but rather broad transitional zones; see also: PROVINCE, (types).

PROVINCE, ALEUTIAN   [need definition]. See also: PROVINCE, (types).

PROVINCE, AUSTRORIPARIAN   That province covering the southern and southeastern coastal plain and characterized by the presence of Polygyra septemvolva and Polygyra auriculata. Similar to the TEXAN PROVINCE which is characterized by Polygyra texasiana. See also: PROVINCE, (types).

PROVINCE, BOREAL   A cold-water zone, depauperate of species, lying north of Cape Cod and the CAROLINIAN PROVINCE. See also: PROVINCE, (types).

PROVINCE, CALIFORNIAN   A cool-water region stretching from Washington (below the ALEUTIAN PROVINCE) to parts of Lower California (above the Panamic Province), and rich in abalones, Murex rock shells, limpets, and chitons. See also: PROVINCE, (types).

PROVINCE, CARIBBEAN   A warm-water region centered in the West Indies, extending north to the Florida Keys and Bermuda, and southward to Brazil. Characteristic species are the QUEEN CONCH, Wide-mouthed Purpura and the Sunrise Tellin; see also: PROVINCE, (types).

PROVINCE, CAROLINIAN   A temperate-water region extending from the south shore of Cape Cod to the northern half of Florida and westward to Texas. It is characterized by QUAHOG clams (Mercenaria), See also: PROVINCE, (types).

PROVINCE, CUMBERLAND   A subdivision of the EAST AMERICAN PROVINCE. This is the most distinct province in the eastern division, typified by the genera: Clappiella, Gastrodonta, Pilsbryna, and Vitrinizonites. See also: PROVINCE, (types).

PROVINCE, EAST AMERICAN   That zone extending from the plains bordering the eastern limit of the rocky mountains the Atlantic Coast. It is further subdivided into the NORTH AMERICAN, INTERIOR, CUMBERLAND, TEXAN, and AUSTRORIPARIAN PROVINCES. See also: PROVINCE, (types).

PROVINCE, INDO-PACIFIC   The largest and richest shell region in the world. Its boundaries extend from East Africa eastward through the East Indies to Polynesia. The region is characterized by tropical, warm waters and coral reefs. See also: PROVINCE, (types).

PROVINCE, INTERIOR   A subdivision of the EAST AMERICAN PROVINCE. See also: PROVINCE, (types).

PROVINCE, JAPANESE   That temperate region lying between the cold-water ALEUTIAN PROVINCE and the tropical Indo-Pacific. See also: PROVINCE, (types).


PROVINCE, MEDITERRANEAN   That region consisting of the Mediterranean Sea and extending around Portugal to southern France and along the northwest coast of Africa; = LUSITANEAN PROVINCE. See also: PROVINCE, (types).

PROVINCE, MIDDLE AMERICAN   The terrestrial faunal province which includes the south tip of Florida and Texas, the West Indies, Bermuda, Central America and most of Mexico. See also: PROVINCE, (types).

PROVINCE, NORTH AMERICAN   A subdivision of the EAST AMERICAN PROVINCE. The Northern Province does not differ greatly in the characteristics of its land snail fauna from that of the INTERIOR PROVINCE, but its climate is too severe for any but the most hardy species. It is typified mainly by small zonitids and pupillids. See also: PROVINCE, (types).

PROVINCE, PANAMIC   That tropical region extending from the Gulf of California to northern Ecuador. Because it was connected to the Caribbean in past geologic times, the fauna resembles that of the West Indies. The region is typified by presence of the genus Strombina. See also: PROVINCE, (types).

PROVINCE, SOUTH AFRICAN   A cool-water region around the southern tip of Africa, the zone is rich in giant limpets, turbans, Thais rock shells, plus strange cool-water cowries and cone shells. See also: PROVINCE, (types).

PROVINCE, TEXAN   That province covering most of Texas, that is typified by the presence and abundance of Polygyra texasiana and related species. Similar to the AUSTRORIPARIAN PROVINCE which is typified by other species of Polygyra. See also: PROVINCE, (types).

PROVINCE, WEST AMERICAN   That faunal province west of the rockies. See also: PROVINCE, (types).

PROVINCULUM   A primitive hinge composed of minute teeth developed before the permanent DENTITION in some bivalve molluscs. The median part of hinge margin of the PRODISSOCONCH, usually bearing small teeth or CRENULATIONS.

PROXIMAL   Nearest to the base or point of attachment; opposite of DISTAL; see also: CONTIGUOUS.

PSEUDOCARDINAL   [need definition].

PSEUDOCARDINAL TOOTH   Tooth irregular in form situated close to the beak (as in some Unionaceans).

PSEUDOCONCH   [need definition]; present in the Cymbulidae (Opisthobranchia: Thecosomata).

PSEUDOCTENODONT   With numerous short HINGE TEETH transverse to the HINGE MARGIN, but descended from forms in which some teeth were longitudinally directed and more or less elongate; see also: CTENOODONT; DENTITION; PSEUDOTAXODONT.

PSEUDOLATERAL TOOTH   LATERAL TOOTH, proximal end of which is close to the BEAK.

PSEUDOPILLAR   Low, broad, inward projection of shell wall (present in some RADIOLITIDS); see also: PILLAR.

PSEUDOTAXODONT   With numerous irregular short HINGE TEETH transverse to HINGE MARGIN and known to be unrelated to CTENODONT and PSEUDOCTENODONT forms; see also: DENTITION; TAXODONT.

PSEUDOUMBILICUS   An opening formed by the distal portions of the canals of previous varices that are arranged obliquely but adjacent to one another to form an UMBILICUS-like pit (as in the Muricidae). See illustration: Composite Gastropod.

PTERIIFORM   A shape exemplified by the bivalve genus Pteria. See other bivalve shapes.
Photo: Pteria colymbus (Roding, 1798)

PTEROPOD   A member of the group of pelagic gastropods (Pteropoda) known as "SEA BUTTERFLIES" and belonging to the orders Thecosomata and Gymnosomata; see also: HETEROPOD.

PULMONATE   A member of the air-breathing subclass of gastropod molluscs, the Pulmonata.

PUNCTATE   With many pinprick-like depressions. See illustration: Composite Gastropod and Composite Bivalve. See also: PIT; QUINCUNX.
Photo: Acteon punctostriatus (C.B. Adams, 1840)

PUNCTATION   Any pattern of many minute PITS; see also: PUNCTATE.

(pl. PUNCTA, never PUNCTAE)
  A pinprick-like depression of the surface; see also: PIT.

PUPIFORM   Shaped like members of the genus Pupilla [Pupillidae]. See other gastropod shapes.

PUSTULATE   Having a knobby texture, the knobs generally smaller than tubercles; PUSTULOSE; see also: MAMMILLATE; PAPILLATE; TUBERCLES.

PUSTULE   A pimple-like or blister-like swelling; see also: GRANULE; PROCESS.

PUSTULOSE   Full of pustules; = PUSTULATE. See illustration: Composite Gastropod.

PYRAMIDAL   Having the form of a solid triangle, i.e., formed like a pyramid.

PYRIFORM   Shaped like a pear.

QUADRANGULAR   Having four sides and four angles.

QUADRATE   Square or rectangular in general outline; applied to the outline of shells which is formed by nearly straight lines meeting at approximately right angles; see also: HEXAGONAL; POLYGONAL; OCTOGONAL; RHOMBOID; SUBQUADRATE; TRAPEZIFORM; TRAPEZOIDAL.
See other bivalve shapes.
Photo: Mysella sp. undet.

QUAHOG   The "hard shell clam" Mercenaria mercenaria. Pronounced: KO-hawg. The young clams are called LITTLENECK clams and the older (but not fully mature and huge) are called CHERRYSTONE clams.

QUATERNARY   Of the fourth order, generally indicating little prominence or strength, as in sculptural elements; see also: PRIMARY; SECONDARY; TERTIARY.

QUEEN CONCH   A strombid gastropod, Strombus gigas. See also: ROLLER.

QUENSTEDT MUSCLE   Small muscle of unknown function represented by scar below LIGAMENT area in Ostreidae.

QUINCUNX   An arrangement of 5 objects (such as dots, or pits) in a square or rectangle, one at each corner and one in the middle (pronounced: kwin' kungks); such arrangements of pits are often found in the Polyplacophora or CHITONS.

RACHIDIAN TOOTH   The central tooth of a RADULA; see also: RADULA FORMULA.


RACHIS   The stem or main shaft of the PEN of a SQUID. See also: VANE.

RADIAL   Arranged in a ray-like pattern; characterized by divergence from a center; = RADIATING.

RADIAL AREAS   In CHITONS (the Polyplacophora), the terminal areas plus lateral areas of the MEDIAN VALVES (which show radiating sculpture).

RADIAL CORD   [need definition]. See illustration: Composite Bivalve.

RADICATED   Attached, and as if it were rooted by means of a fibrous BYSSUS; see also: ATTACHED.

RADIOLITID   [need definition].

  A ribbon which supports rows of chitinous teeth; this characteristic is found only in molluscs; see also: ASCUS SAC; CUSPIDOBLAST; ODONTOPHORE; RADULA FORMULA; UNISERIATE.

Mikkelsen, P.S. 1985. A rapid method for slide mounting of minute radulae, with a bibliography of radula mounting techniques. Nautilus 99(2-3):62-65. [request a reprint! or download a copy]

RADULA FORMULA   A series of numbers indicating the number of MARGINAL TEETH, LATERAL TEETH and the RACHIDIAN TOOTH, and (again) the lateral teeth and marginals.
Example: a formula of 3+6+R+6+3 indicates 3 marginal teeth, 6 lateral teeth and 1 rachidian (R) tooth. The radula formula may be simply "1" if the radula is UNISERIATE, having only rachidian teeth. See also: DOCOGLOSSATE; STENOGLOSSATE; RHIPIDOOGLOSSATE; TAENIOGLOSSATE; TOXOGLOSSATE.

See the excellent illustrations on Wikipedia.

RADULA RIBBON   The flexible structure in which the radular teeth are embedded; see also: RADULA.

  Having projecting parts or branches. See also: BIRAMOSE; TRIRAMOSE.

RAMP, SUTURAL   [need definition]. See illustration: Composite Gastropod.

(pl. RAMI)
  A branch or leaf-like process, generally borne distally on a SPINE.

RANGE   The geographic limits within which a species lives.

RAPHITOMA BICOLOR   [need definition].

  Common name applied to the ELONGATE bivalve shells of the genus Solen.
Photo: Solen viridis Say, 1821

RECENT   The present geologic epoch (the word Recent is usually capitalized when used in this manner).

RECESSED   Situated within a cavity, as within the APERTURE; opposite of PROTUBERANT.

RECTILINEAR   In a straight line; see also: LINEAR.

RECURVED   Curved or bent backward; when used in reference to symmetrical CONICAL univalves, signifies that the apex is turned towards the posterior margin (as in Emarginula spp.); see also: DEFLEXED; REFLECTED; REFLEXED.

REFLECTED   Bent backwards; reflexed; see also: INFLECTED; RECURVED; DEFLEXED; REFLEXED.

REFLEXED   [need definition]. See also: DEFLEXED; RECURVED.

REMOTE   Distant from the point of reference; used in reference to LATERAL HINGE TEETH which are placed at a distance from the cardinal teeth; see also: DISTAL.

RENIFORM   Shaped like a kidney (e.g., the aperture of Ampullaria spp.).

REPENT   Descriptive of shells which, being ATTACHED by the whole length of their shell, give the appearance of creeping or crawling.

RESILIAL PIT   One of a series of small pits in line below the RESILIUM. These occur in three genera: Mytilus, Mytella and Perna.

RESILIAL RIDGE   The point of attachment of the LIGAMENT. See also: RESILIUM.

  The socket-like structure (fossette or CHONDROPHORE, depending on shape) that supports the INTERNAL LIGAMENT in certain bivalves. See also: BOURRELET.

RESILIUM   An internal ligament, irrespective of composition ("cartilage" of earlier authors), in a resilifer and under compressional stress; see also: LITHODESMA; RESILIFER; RESILIAL PIT; RESILIAL RIDGE; TENSILIUM.

RESORBED   Dissolved and removed from a solid structure, as in the removal of a portion of the shell's surface in order to permit further growth of the shell after a resting stage (marked in the Muricidae by a VARIX).


RESTING STAGE   A stage between periods of active growth, marked in the shell by the formation of a varix.

RETICULATE   Netted; covered with a network. See illustration: Composite Bivalve. See also: CANCELLATE.
Photo: Cancellaria reticulata (Linne, 1767)

RETRACTED   In gastropods, the state of the animal being withdrawn into its shell; also the condition of its TENTACLES being withdrawn or (in NUDIBRANCHS) a BRANCHIAL PLUME being withdrawn. In bivalves, the condition of the clam having its FOOT and/or SIPHONS withdrawn. See also: EXTENDED.

RETRACTILE   Capable of reducing length by inverting like a glove when the fingers are withdrawn; see also: CONTRACTILE; INVERSIBLE.

RETRACTOR MUSCLE   [need definition]; see also: ADDUCTOR MUSCLE.


REVOLVING   Of cords or grooves on a snail shell, turning with whorls, or spirally. .


RHINOPHORE   One of a pair of olfactory tentacles in the true NUDIBRANCH and shelled OPISTHOBRANCHS which replaces the lost OSPHRADIUM; in gastropods, the posterior pair of TENTACLE. See illustration: Composite Nudibranch.

RHIPIDOGLOSSATE   A type of RADULA with the RADULA FORMULA consisting of a RACHIDIAN TOOTH, with 3 or more MARGINAL teeth and numerous LATERAL teeth.

Pilsbry, H.A. 1889. The radula in rhipidoglossate molluscs. Proc. Acad. Nat. Sci. Phila. 41:136-137.

RHOMBOID   Roughly diamond-shaped, with 4 equal sides and no right-angled corners; see also: QUADRATE.

RHYNCHOTEUTHIS   A LARVAL stage of the CEPHALOPOD family Ommastrephidae (a taxonomic group of SQUID).

RHYTHMICAL SEXUALITY   A type of PROTANDRY in which there is a regular return to the male phase after the eggs are laid.

RIB, AXIAL   [need definition]. See illustration: Composite Gastropod. See also: SCLEROCHRONOLOGY; VARIX.

RIB, CONCENTRIC   A RIB that follows COLLABRAL LINES. See illustration: Composite Bivalve.

RIB, DIRECTIVE   A rib, forming a part of surface ornament of a shell, that lies entirely within a single plane; see also: DIRECTIVE SPIRAL.

RIB, DIRECTIVE   A RIB, forming part of surface ORNAMENTATION of shell, that lies entirely within a single plane.

RIB, LABIAL   A varix; a thickened or extensive AXIAL RIB.

RIB, LONGITUDINAL   [need definition]. See illustration: Composite Gastropod.

RIB, RADIAL   A RIB emanating outward from a central point of origin, usually along with other ribs. See illustration: Composite Bivalve.
Photo: Anadara ovalis (Bruguiere,1789)

RIB   A raised, elongate structural element, generally axially oriented; see also: RIB, (types); RIB-STRIAE; RIBLET; RIPPLED; STRIAE; VARIX.


RIBLET   A minor rib; see also: STRIAE.

RIBLET, PRIMARY   On shell with riblets of different orders of strength, the riblet that appears early in ontogeny and remains longer than those appearing later; see also: RIBLET, SECONDARY.

RIBLET, SECONDARY   On shell with riblets of different orders of strength, the riblet that appears somewhat later in ONTOGENY than primary riblets and remains weaker than these; see also: RIBLET, PRIMARY.

RIB-STRIAE   Transverse undulations of the shell surface which are more prominent than STRIAE but less prominent than RIBS; see also: STRIAE; RIB; RIBLET.

RIDGE   [need definition].


(abbrev: RV)
  That valve of a bivalve lying on the observer's right-hand side when the shell is placed with anterior end pointing away from the observer, and with COMMISSURE vertical, the hinge being uppermost; see also: LEFT VALVE. Visit Let's Talk Seashells for how to distinguish between right and left valves.

RIGICLAUDENT   A type of OPERCULUM that does not flex upon retraction. See also: FLEXICLAUDENT.

See the 1998 article by Checa and Jiménez-Jiménez: Constructional morphology, origin, and evolution of the gastropod operculum..

RIPPLED   Finely and indistinctly RIBBED.

ROBUST   Strong in structure; prominently formed; opposite of WEAK.

ROLLER   Common name for a JUVENILE specimen of the Queen Conch, Strombus gigas; without the flared outer lip of a mature specimen, the shell has a greater tendency to roll in strong currents.
Photo: Strombus gigas Linne, 1758

ROSTRATE   Having a beak-like projection (as in a long, straight SIPHONAL CANAL, e.g. Cuspidaria spp.); = NUCULANIFORM; see also: BEAK. See other bivalve shapes.

ROSTROCONCH   A member of the molluscan class Rostroconchia, a group of extinct (from the Paleozoic era) molluscs with pseudo-BIVALVED shells, as adults; probable ancestors of BIVALVES. See the Paleos website for definition, references, images, and systematics.

ROSTRUM   [need definition].

ROTUND   Approximately circular or globular.

ROUNDED   Having an evenly curved periphery; not angulate or CARINATE; see also: WHORL, ROUNDED.

RUDIST   An extinct group of marine HETERODONT bivalves. For a detailed definition, see Wikipedia.

RUFFLED   Having many erect LAMELLAE, like a ruff.

RUFOSE   Reddish or reddish-brown colored; = RUFOUS.

(pl. RUGAE)
  An irregular fold in the surface SCULPTURE.

RUGOSE   Full of wrinkles or ripples; see also: WRINKLED.

RV   Abbreviation for "RIGHT VALVE" of a bivalve shell. See also: LV.

SACOGLOSSAN   Old, outdated term for ASCOGLOSSAN.

SAGITTAL   Anteroposteriorly directed plane of symmetry of shell and soft parts.

SAND COLLAR   The egg mass of the MOON SNAIL. A circular ring, with a larger diameter at the base, of ribbonlike material composed of hardened mucous, sand and egg capsules of the Moon Snail.

SARCOBELUM   In some slugs, the dart sac is lost as such, and is converted into an exertile stimulating organ, the sarcobelum; see also: DART SAC.

SCABROUS   Rough; covered with minute points, DENTICLES, or SCALES.

SCABROUS LAMELLAE   Thin LAMELLAE having scale-like projections at their intersections with spiral cords.

SCALARIFORM   Loosely coiled; see also: TIGHTLY COILED.

SCALE   Thin, erect, plate-like structures; a localized, thin and flat projection of the outer layer of shell, commonly situated on a COSTA; see also: IMBRICATE; SQUAMOUS; VAULTED SCALE.

SCALE   [need definition]. In CHITONS… See illustration: Composite Chiton.

SCALLOP   Bivalves of the family Pectinidae and (Glass Scallops) Propeamussiidae; See also: PECTINITE. See Henk Dijkstra's website on Scallops.

SCALLOPED   Edged with rounded projections.

SCAPHOCONCHA   The secondary shell of the ECHINOSPIRA larva. See also: VELICONCH.

SCAPHOPOD   A member of the class Scaphopoda, a group of molluscs made up of [need definition]. Also commonly called a TUSK SHELL. See also: CAPTACULA. See illustration at UCMP.


SCHIZODONT   Descriptive of an ACTINODONT bivalve HINGE of which the individual teeth have DENTICULATED edges, with one tooth (median of LV) broad and bifid; see also: ACTINODONT; DENTITION.

SCIENTIFIC NAME   The Latin BINOMIAL name applied to SPECIES, comprised of the GENUS and SPECIES name legally proposed according to the rules of the ICZN. See also: COMMON NAME.

SCISSULATE   Diagonal sculpture across a shell. See also: DIVARICATE.

SCISSULATIONS   The wavy sculptural lines on many shells, such as the tellins.

SCLEROCHRONOLOGY   The study of the formation and interpretation of growth increments in accretionary hard parts of invertebrate and vertebrate organisms as well as coralline red algae. See also: GROWTH RING VARIX.

See also:
1st International Sclerochronology Conference, St. Petersburg, Florida USA; July 17-21, 2007.
2nd International Sclerochronology Conference, Mainz, Germany; July 24-28, 2010.
Conference Proceedings

3rd International Sclerochronology Conference, Caernarfon, North Wales, UK; May 18-22, 2013.

SCROBICULATE   Having small ditches or FURROWS marked on the surface; see also SULCATE.


SEA BUTTERFLY   Members of the PLANKTONIC group of molluscs known as PTEROPODS; see also: HETEROPOD.

SEA HARE   Members of the suborder Aplysiomorpha (Opisthobranchia).


  Snails of the genus Janthina which float in the open sea as part of the PLANKTON. Their purple shell color is acquired from their food source, siphonophores such as the Portuguese Man of War, Physalia physalis, the By-The-Wind Sailor, Velella vella, and Blue Buttons, Porpita porpita.

SEALED   Closed; said of the siphonal canal, anal tubes, or spines; see also: COALESCED; SEAM.

SEAM   A closure line, along which two surfaces are fused; see also: SEALED.

SECONDARY   Less than primary in strength; second order; see also: PRIMARY; TERTIARY; QUATERNARY.

SECONDARY HOMONYM   A homonym that results from one SPECIES being placed into a GENUS where the species name is in use for a different species. The older of the two names is the senior secondary homonym. See also: HOMONYM; PRIMARY HOMONYM; HOMONYMY.

SECURIFORM   Hatchet-shaped.

SEDENTARY   Staying in one place; see also: NESTLER; SESSILE.

SELENIZONE   The spiral band of crescentic growth lines generated by a NOTCH or narrow slit in the Archaeogastropods; a slit band (e.g., the slit of the "SLIT SHELLS" such as Pleurotomaria spp.; Bayerotrochus spp.).

SEMICORDATE   Half heart-shaped; see also: CORDATE; CORDIFORM.

SEMIDISCOIDAL   Forming half of a circular disk; see also: DISCOIDAL.

SEMILUNATE   Half moon-shaped; see also: LUNATE.

(abbrev: SL or S.L.)
  In the broad sense (used with respect to taxonomic categories); e.g., Strombus sensu lato = all subgenera in the genus Strombus; see also: SENSU STRICTO.

(abbrev: SS or S.S.)
  In the strict sense (used with respect to taxonomic categories); In the restricted sense (e.g., Strombus, sensu stricto = the subgenus Strombus itself and not any of the other subgenera in the genus Strombus) = Strombus Strombus spp.; see also: SENSU LATO.

SEPTIBRANCH   [need definition].

SEPTUM   A deck-like shelly process in the anterior end of some bivalves.

SERRATE   Finely notched or saw-like at the edge; see also: DENTICULATE.

SERRATION   A single tooth in a NOTCHED edge.

SESSILE   Living attached (usually permanently) to a substrate; see also: NESTLER; SEDENTARY

SETIFEROUS   Hairy; see also HIRSUTE.

SHELF   A flattened surface, as on the upper portion of a PLAIT or CARINA. The DECK of a Crepidula shell.

SHELL   The CALCAREOUS structure secreted by the molluscan MANTLE. Most mollusks have external shells, some have internal shells, and others (as adults) have no shell; = TEST.

SHELL CLUB   An organized group of individuals, amateur and professional, interested in the phylum Mollusca. Although the name implies only shells (of marine, freshwater, terrestrial, arboreal, marine and fresh water molluscs), club members often have broader interests to include those molluscs without shells as adults (e.g., nudibranchs, ascoglossans, cephalopods, aplacophorans). Typically, regular meetings are held, presentations are made, and field trips organized; often, a newsletter and/or website is published. A list of shell clubs (and related organizations) is maintained on the Conchologists of America (COA) website. See also: MALACOLOGICAL SOCIETY.

SHELL COLLECTION   An accumulation of molluscan shells. This collection can vary from a basket of shells to a massive amount of shells, all of which are (typically) cataloged with a taxonomic name and (more importantly) collection data. Professional collections are maintained at a variety of museums, for example the United States National Museum (USNM), Philadelphia Academy of Natural Sciences (ANS), etc. Many "shell collections" are better classified as mollusc collections because they contain the preserved shelless molluscs as well. Often the professional collections are repository sites for TYPE SPECIMENS. Some "shell" collections (or sub-collections) may be entirely of a variety of OPERCULA.

SHELL GLAND   The gland that secretes the shell for the PRODISSOCONCH I.

SHELL SHOW   An event, usually hosted by a SHELL CLUB, where many people display ("show") their shells (a portion of their SHELL COLLECTION) to the public. The displays usually are submitted in various categories (e.g., scientific, MINIATURES, art, one family, one species, etc.) for judging by selected experts. Ribbons, plaques, trophies, etc. are awarded to selected displays. A list of shell shows (and related events) is posted on the COA website.

SHELLFISH   A culinary term referring to edible shelled molluscs (as well as some crustaceans and echinoderms), including (but not limited to): MUSSELS, QUAHOGS, SCALLOPS, and PERIWINKLES.

SHELLFISH LISTSERV   A mailing list on a LISTSERV hosted by the National Shellfisheries Association (NSA). "The purpose of the Forum e-mail list is to promote open exchange of ideas among those working with or interested in any aspect of shellfisheries - research, management, regulation, commercial production, etc."

Another "SHELLFISH" mailing list is provided by the Washington State Department of Health as a service to the shellfish industry and partner agencies and organizations who are involved in commercial shellfish harvest management.

See the compilation of information about Molluscan Listserves.


SHIELD, PARIETAL   [need definition]. See illustration: Composite Gastropod.

SHIPWORM   Bivalves of the genera Teredo and Bankia which, in addition to wharf pilings and other wood, bore into ships with wooden hulls, often in great numbers and impacting the integrity of the wood to the point of destroying the ships (sometimes while at sea!); see also: BORING BIVALVE; TEREDINIFORM.
Illustration: Teredo sp. (left = entire animal; center = PALLETS; right = shell)

SHOULDER   The portion of each whorl of a gastropod shell lying between the SUTURE and the angle, periphery, or SHOULDER margin. See illustration: Composite Gastropod.

SHOULDER MARGIN   The periphery or outermost edge of a WHORL.

SHOULDER SPINE   A spine at or above the SHOULDER margin.

SHOULDERED   Having an angulation of the whorl at its periphery or outermost edge, even if this is indefinite, as in the case of a CONVEX profile.

SICKLE-SHAPED   Strongly curved in a single arc.

SIMPLE   Single, entire, uninterrupted or undivided; see also: CONTINUOUS; HOLOSTOMATE.

SINISTRAL   In gastropods, the direction of coiling in which, with the shell held upright (apex at the top), the APERTURAL opening is at the left; and in which, with the shell viewed from above the APEX, the coiling proceeds from the apex in a counterclockwise direction; = LEFT HANDED; opposite of DEXTRAL; See also: ACHIRAL; CHIRALITY; HETEROSTROPHY; ENANTIOMORPH;.
See other gastropod shapes.
Illustration: Physella sp.; Photo: Busycon contrarium (Conrad, 1840)
See: Sinistral Shells - by design or accident

SINOPALLIATE   The condition. in bivalves, of having a PALLIAL SINUS; see also: INTEGROPALLIATE.

SINUATE   Curved; excavated.

SINUOUS   Winding.


SINUS   A bend or embayment, either in growth lines or in the attachment scar of the MANTLE; PALLIAL SINUS.

SIPHON   A tubular fold of MANTLE tissue, for the passage of water currents, whether INHALENT or EXHALENT in BIVALVES. In SQUID, this is an organ of propulsion.

SIPHONAL AREA   Posterior sector of surface of shell, commonly demarcated anteriorly by an UMBONAL ridge; secreted where mantle edge has openings or is produced to form SIPHONS for passage of respiratory currents.

SIPHONAL BAND   Longitudinal band (one of two) on the surface of some RUDISTS (mainly RADIOLITID) differing in ornament from the rest of the surface and thought by some to have been secreted at part of MANTLE EDGE where respiratory current entered or left the shell.

SIPHONAL CANAL   A complete or incomplete tubular shell extension through which the anterior SIPHON is extended; if protruded, this is called a ROSTRUM; = CAUDAL CANAL; = ANTERIOR CANAL. See illustration: Composite Gastropod. See also: BASAL FOLD; SPOUT.

SIPHONAL FASCIOLE   A ridge formed on the SIPHONAL CANAL, sometimes bearing remnants of previous canals. See illustration: Composite Gastropod.

SIPHONAL NOTCH   [need definition]... See also: SIPHONOSTOMATE.

SIPHONAL RETRACTOR MUSCLE   Muscles serving to withdraw SIPHONS partly or wholly within shell.

SIPHONAL SCAR   The opening or winding sinus in the PALLIAL impression of a bivalve shell, in the place where the animal's siphonal tube passes.

SIPHONAL SINUS   [need definition]; see also: BASAL FASCIOLE.

SIPHONOPLAX   One of the shelly ACCESSORY PLATES in the Pholadacea; a tubular secondary CALCAREOUS structure forming a posterior extension of the shell in some Pholadidae and protecting the proximal end of the SIPHONS; see also: HYPOPLAX; MESOPLAX; METAPLAX.

SIPHONOSTOMATE   Descriptive of a shell with a discontinuous PERISTOME, interrupted anteriorly by a sinus that may be prolonged into a shell siphon, called the SIPHONAL NOTCH or canal; = SIPHONOSTOMATOUS; see also: HOLOSTOMATE.


SIPHUNCLE   In CEPHALOPODS, the delicate, hose-like extension from the VISCERAL MASS that runs through all the chambers of the shell in Nautilus and Spirula; a small SIPHON; see also: PHRAGMOCONE.

See the excellent "Cephalopod Glossary" by Richard E. Young, Michael Vecchione, and Katharina M. Mangold.

SLIPPER SHELL   Gastropods of the genus Crepidula where the underside of the shell has the appearance of a slipper. See also: DECK; DIAPHRAGM.

SLIPPER-SHAPED   Resembling a person's slipper, e.g., when viewing an upside-down shell of the genus Crepidula, with the DECK of the shell forming the upper part of the slipper. See other gastropod shapes.


SLIT SHELL   A SNAIL of the family Pleurotomariidae. These snails have a slit called a SELENIZONE.

SLOPE, SUTURAL   [need definition]. See illustration: Composite Gastropod.

SLUG   A common designation for a SNAIL without an external shell; the shell is either rudimentary and enclosed in the MANTLE, or wanting entirely; see also: SLUG, SEA.

SMOOTH   Not rough; lacking SCULPTURE. See illustration: Composite Bivalve. See also: MALLEATE


SNAIL FUR   Common term for ORNAMENTATION in which epibionts (e.g., Hydractinea spp.) are attached to and cover gastropod shells.
See: Epibiotic on Ilynanassa trivittata, Hydractinia echinata - Snail Fur

SOCKET   In bivalves, a recess for the reception of a HINGE TOOTH from the opposite VALVE.

SOLENOGASTER   Common name for a member of the molluscan class Aplacophora.

SOLID   Strong, thick, or sturdy; see also: STOUT.

SPADIX   A HECTOCOTYLISED special portion of the TENTACLE crown of Nautilus, involving four TENTACLES of one of the lobes of the right side; this forms a sleeved projection with a glandular tip; see also: HECTOCOTYLUS.

SPAT   The settled, newly-attached to the substrate LARVAE of OYSTERS (the Ostreidae), usually, but can refer to that of any bivalve. The spat metamorphose to form a juvenile clam, which matures attached to the substrate at that location for the rest of its life.

SPATHATE   [need definition]; (see description of Aequipecten glyptus in: Abbott, 1974.)

SPECIES   [need definition]; see also: SUBSPECIES; DIAGNOSIS.

(abbrev: SP. NOV.;
  A new SPECIES; Used in publication the first time (and first time only!) that a new BINOMEN is presented; e.g. "Acteocina atrata, spec. nov." as published in The Veliger 27(2):164-192. See also: GENUS NOVUM

SPECIMEN   [need definition].


SPERMATHECA   [need definition].

SPERMATOPHORE   A CHITINOUS envelope which encloses SPERM, and is secreted by the male duct in the FLAGELLUM, a tubular outgrowth of the PENIS; see also: CEMENT BODY.

SPICULE   One of the small, slender, pointed, hard bodies in the integument, which serves as stiffening. Spicules may be prominent in the GIRDLE of CHITONS. See illustration: Composite Chiton.

SPINATION   The total complement of spines; the spine pattern.

SPINDLE-SHAPED   Round; tapering toward each end; FUSIFORM. See other gastropod shapes.
Photo: Triplofusus giganteus (Kiener, 1840)

SPINE   A more or less slender and elongate projection of a shell, either tapering to a point or spreading out distally into fronds or FOLIATIONS. See illustration: Composite Gastropod and Composite Bivalve. See also: SPINELET; SPLIT SPINE.

SPINE-TUBE   A tapering SPINE having a hollow interior.

SPINIFEROUS   Bearing many spines; = SPINOUS.

SPINOUS   Bearing many spines; = SPINIFEROUS; see also: ACULEATE; MURICATED.

SPIRAL   Revolving, as lines going in the direction of the turning of the WHORLS; see also: LOGARITHMIC SPIRAL; SUBSPIRAL.

SPIRAL CORD   [need definition]. See illustration: Composite Gastropod.

SPIRAL GROOVE   A GROOVE that encircles the spire of a shell. Revolving grooves going in the direction of the turning of the whorls. Coarser than a SPIRAL THREAD.
Photo by Marlo F. Krisberg; Echinolittorina riisei (Mörch, 1876).

SPIRAL SCULPTURE   Sculpture following the HELICAL growth of the gastropod shell.


SPIRE   [need definition].

SPIRE ANGLE   The angle at which the whorls of a spire increase in size. See illustration: Composite Gastropod.

SPIRE WHORL   One turn (360 degrees) of the spire, exclusive of the BODY WHORL.

SPIRE, INVOLUTE   The condition of having the POSTNUCLEAR WHORLS higher than, and enveloped by the NUCLEAR WHORLS; see also: SPIRE, SUNKEN.

SPIRE, SUNKEN   The condition of having the POSTNUCLEAR WHORLS higher than the spire, or NUCLEAR WHORLS (the nuclear whorls are not hidden from view, as with an involute spire); see also: SPIRE, INVOLUTE.

SPIRE   The cone of whorls produced, by the downward growth from the APEX, of shelled, non-symmetrical gastropods, including all whorls above the aperture. See illustration: Composite Gastropod. See also: SPIRE ANGLE.

SPIROGYRATE   Coiled outward from the SAGGITAL plane; term applied to the UMBONES of bivalves; see also: OPISTHOGYRATE; ORTHOGYRATE.

SPLANCHNIC GANGLION   That portion of the CEPHALOPOD nervous system which is responsible for the well-integrated rhythms of the complicated stomach and DIGESTIVE GLAND.

SPLIT SPINE   A SPINE with incurled, but not fused margins.

SPLITTER   In taxonomy, one who recognizes more species because they believe that differences between two or more PHENOTYPES are species specific and that they all should be treated as more than one species. See also: LUMPER.

SPLITTING   Opposite of LUMPING, i.e., the perception of a multiplicity of forms and the acceptance of them as discrete entities, while others may consider the same group as one entity.

SPOUT   An elongated, tube-like canal structure.

SQUAMOUS   Scaly; with the appearance of being scaly; see also: IMBRICATE.


SQUID   [need definition]. A CEPHALOPOD… see also: GIANT SQUID.

See the detailed web page on squid terminology, from the excellent "Cephalopod Glossary" by Richard E. Young, Michael Vecchione, and Katharina M. Mangold.

STEAMER   A clam, Mya arenaria favored in the northeastern USA for being steamed and eaten; see also: CHERRYSTONE; LITTLENECK; QUOHOG.


STENOGLOSSATE   "Close-toothed" or "narrow-tongued"; pertaining to the Stenoglossa, in which the Muricidae are included; = rachiglossate. The columbellid radula is considered representative of the stenoglossate type of RADULA FORMULA: (see: J. Moll. Stud. (1977), 63:65-67.)


STOUT   Sturdy, solid, or bulky; see also: SOLID.

STREPTONEUROUS   The condition in PROSOBRANCH gastropods of having the mantle cavity and contained organs located anteriorly; see also: EUTHYNEUROUS.

(pl. STRIAE)
  Very narrowly INCISED shallow groove (Cox, 1960); this term especially used to refer to one of a series of parallel or concentric grooves (= striae); see also: LIRA; GROOVE; RIB-STRIAE; RIB.

STRIA, AXIAL   [need definition]. See illustration: Composite Gastropod.

STRIA, RADIAL   A STRIA emanating outward from a central point of origin, usually along with other striae. See illustration: Composite Bivalve.

STRIA, SPIRAL   [need definition]. See also: CORD. See illustration: Composite Gastropod.

STRIATE   Marked with fine parallel GROOVES, scratched, or slightly raised lines or STRIAE; see also: VERMICULATION.

STRIATION   A single line or scratch; a STRIA; a pattern of striae.

STRIGA   A transverse band of color (pl=STRIGAE). See also: STRIGATE .

STRIGATE   Having STRIGAE, or transverse bands of color (i.e., STRIGATIONS).


STROMBOID   Shaped like some members of the genus Strombus. = STROMBIFORM. See other gastropod shapes.
Photo: Strombus raninus Gmelin, 1791

STROMBOID NOTCH   A sinuation in the outer lip of shells of the family Strombidae, or a similar situation in other gastropod shells; see also: TURRID NOTCH.
Photo: Strombus raninus Gmelin, 1791
For another labelled photo, see the site: Seashells of New South Wales

STROMBUS-L LISTSERV   A mailing list on a LISTSERV which is hosted by the Gulf and Caribbean Fisheries Institute (GCFI) and is dedicated to "Queen conch fisheries, management, conservation, aquaculture, restoration".

See the compilation of information about Molluscan Listserves.

STRUT   A SCULPTURAL element lending strength or stiffness to the whole structure.

STUMP   A stub; a small remnant of a structure.


STYLE SAC   That part of the intestine in which the PROTOSTYLE rotates.

SUB   A prefix indicating less than, below, or almost.

SUBACUTE   Only moderately ACUTE.

SUBANGULATE   Weakly angled; OBTUSE.

SUBCENTRAL   Nearly central; slightly off center; see also: CENTRAL.

SUBDUED   Weak; not evident.

SUBELLIPTICAL   [need definition]. See other bivalve shapes.

SUBEQUILATERAL   Applied to bivalve shells which are nearly equal in size; see also: EQUILATERAL; INEQUILATERAL; INEQUIVALVE.

SUBJECTIVE SYNONYMY   A name representing, in the author's opinion, the same entity as that represented by another name; see also: SYNONYM.

SUBMARGIN   One of the dorsal edges of the disk or body of a shell in the Pectinacea, adjoining the lower body of the AURICLE.

SUBMICROSCOPIC   Not clearly visible under a light microscope; see also: MICROSCOPIC.

SUBORBICULAR   Having a shape of a misshapen circle; see also: ORBICULAR. See other bivalve shapes.

SUBOVAL   Like a circle that has been only slightly flattened; see also: OVAL; OVATE.
See other bivalve shapes.

SUBQUADRATE   Not quite QUADRATE, but nearly so; see also: SUBELLIPTICAL.
See other bivalve shapes.

SUBSEQUENT DESIGNATION   The designation of the TYPE SPECIES of a GENUS subsequent to the description of the genus.

SUBSPECIES   [need definition]; see also: FORM; SPECIES; VARIETY.

SUBSPIRAL   Not sufficiently SPIRAL to form a complete VOLUTION.

SUBSTRATE   The surface on which an organism lives, generally underwater; = SUBSTRATUM.


SUBSUTURAL   Below the SUTURE; at the upper margin of the younger (newer) of two successive WHORLS.

SUBTIDAL   Below the lowest tide line and extending generally to the edge of the continental shelf.

SUBTRIGONAL   Not quite TRIGONAL, but nearly so. See other bivalve shapes.
Photo: Nucula proxima Say, 1822

SUCKER   A suction cup on the ARMS and TENTACLES of CEPHALOPODS. See also: ACETABULUM.

SUCTORIAL   Having the mouth parts modified for ingesting juices of plants or soft-bodied animals.

SUFFUSED   Covered over or flushed with a tint of color.

SULCATE   Having a deep slit, FISSURE, or FURROW; see also: SCROBICULATE.

(pl. SULCI)
  A deep slit, fissure, or furrow; see also: SULCUS, ANAL; SULCUS, AURICULAR.

SUMMIT   Most dorsal point of profile of a VALVE (of bivalves) when the specimen is viewed along the CARDINAL AXIS or from the side with the cardinal axis horizontal.

SUPERFLUOUS NAME   An unnecessary name, in most cases one applied to an entity that already has a valid name.

SUPRAPEDAL GROOVE   A groove above, and running parallel to, the PEDAL GROOVE in certain snails.


SURFACE SCULPTURE   The ORNAMENTATION of the exterior of a molluscan shell.

SUTURAL   Referring to or associated with the SUTURE.

SUTURAL SINUS   [need definition].

SUTURAL TUFT   [need definition]. In CHITONS… See illustration: Composite Chiton.

SUTURE   A continuous spiral line following the junction of consecutive WHORLS in a gastropod shell; see also: SUTURE, (types).


SUTURE, CHANNELED   [need definition]. See illustration: Composite Gastropod. See also: SUTURE, ADPRESSED; SUTURE, IMPRESSED

SUTURE, CRENATE   [need definition]. See illustration: Composite Gastropod.

SUTURE, CRENULATE   [need definition].


SUTURE, INDENTED   [need definition].

SUTURE, INDISTINCT   [need definition]. See illustration: Composite Gastropod.

SUTURE, STRONGLY INDENTED   [need definition].

SWELLING   An enlargement, generally GLOBOSE.


SYMPLESIOMORPHY   A character shared by a number of groups, but inherited from ancestors older than the last common ancestor. See also: PLESIOMORPHY.

See the Paleos website for greater detail.

SYNAPOMORPHY   An APOMORPHY shared by two or more groups which originated in their last common ancestor.

See the Paleos website for greater detail.

SYNONYM   One of two or more names given to a SPECIES; customarily, the later of two different names that have been bestowed upon a single species or GENUS... technically, both are synonyms, one senior and the other junior; see also: CHRESONYMY; JUNIOR SYNONYM; SYNONYMY. .

SYNONYMIZE   To state that two or more names represent the same biological entity. See also: SYNONYM.

SYNONYMY   A list of the various different scientific names, regardless of validity or correctness, that have been used to designate a single biological entity. See also: CHRESONYMY; HOMONYMY; SUBJECTIVE SYNONYMY; SYNONYM.

SYNTOPIC   Sharing the same HABITAT within the same geographic locality or range.

SYNTYPE   One of a number of specimens studied by the author of a species name, of which group no single SPECIMEN was designated as a HOLOTYPE.

See the publication: "Terminology of Types" by Frizzell.

SYNTYPIC   Pertaining to a SYNTYPE or syntypes.

SYSTEMATICS   The discipline of biological CLASSIFICATION. One who studies systematics is a SYSTEMATIST.

SYSTEMATIST   One who forms, revises, or adheres to a system of CLASSIFICATION of biological categories; one who studies SYSTEMATICS. See also: TAXONOMIST.

TABULATE   Table-like; sharply angulate (approaching 90 degrees); said especially of the SHOULDER or PERIPHERY of each WHORL.


TAENIOGLOSSATE   A type of RADULA structure consisting of a central RACHIDIAN tooth, a LATERAL lateral tooth, and a pair of MARGINAL teeth (e.g., members of the Cypraeidae and Cymatiidae). This condition is referenced by the RADULA FORMULA: 2+1+R+1+2

TAIL VALVE   The first of (typically) eight valves of a CHITON. See also: HEAD VALVE; MEDIAN VALVE.

See illustration: Composite Chiton.

TANGENTIAL   Divergent, digressive; of the nature of a tangent; touching briefly and then divergent.

TAPERING   Decreasing gradually in circumference; generally said of a cylindrical form or structure.

TAPHONOMY   Referring to the immediate post-mortem period between death and final entombment of the skeletal remains in the sediment; see also: FOSSIL.

TAUTONYMY   A situation in which the type species of a genus is designated as such by virtue of having a specific name identical to that of the newly erected generic name.

TAXODONT   Having numerous short HINGE TEETH more or less similar in shape and mostly set at an angle to the HINGE MARGIN. See illustration: Composite Bivalve. See also: DENTITION; PRIONODONT; PSEUDOTAXODONT.

(pl. TAXA)
  A grouping of organisms under a "common" (i.e., single) name; a unit of classification at any level, implying biological relationship.

TAXONOMIST   One who studies TAXONOMY.

TAXONOMY   The classification of animals or plants according to relationship; One who studies taxonomy is a TAXONOMIST. See also: SYSTEMATICS.

TECTIBRANCH   Molluscs of the order Cephalaspidea, or "BUBBLE SHELLS" usually having a shell present, gills present, head with a tentacular shield, jaws feeble or none, stomach usually with GIZZARD PLATES, and with or without an OPERCULUM.

TEETH   In bivalves, the shelly protuberances on the dorsal margin of a VALVE which fit into corresponding sockets of the opposite valve.

In gastropods, the RADULA.

In cephalopods, see: BEAK.

TEGMENTUM   Outermost layer, with SCULPTURE and coloration, of a CHITON shell.

  The gastropod shell, apart from the NUCLEUS; = POSTNUCLEAR WHORLS; complement of the PROTOCONCH; see also: ADULT WHORLS.

TELEODONT   With differentiated CARDINAL TOOTH and LATERAL TEETH, as in DIAGENODONT forms, but with additional elements giving rise to more complicated hinge (example: Venus); see also: DENTITION.

TELUM AMORIS   The "love dart" produced by the DART SAC; it is about 5/16 of an inch long and delicately ridged, finely pointed, and calcareous; it is exchanged by the partners with some velocity before courtship, lodging in the integument and serving as a releaser stimulus for courtship behavior.

TENSILIUM   The outer band of the LIGAMENT, composed of CONCHIOLIN but without lime, usually with a conchoidal fracture, it is HORNY and tensional.

TENTACLE (1)   In snails: an elongate sensory structure on the heads of snails; in some groups (e.g., Stylommatophora) it bears an eye at its tip, while in others (e.g., Basommatophora) at the base; see also: CEPHALIC TENTACLE; RHINOPHORE; EYE STALK.

TENTACLE (2)   In squid, one of the 4th pair (dorsal pair = No. 1) of the 5 pair of appendages surrounding the mouth; usually longer than the "ARMS"; (the other 4 pair of appendages) and extensible; see also: HECTOCOTYLUS.

See the detailed web page on tentacle terminology, from the excellent "Cephalopod Glossary" by Richard E. Young, Michael Vecchione, and Katharina M. Mangold.

TENTACLE, CEPHALIC   A tentacle on the head. In gastropods, the anterior pair of tentacles; see also: RHINOPHORE.

TENTACLE, EPIPODIAL   A tentacle on the FOOT, or (in some species) arising from a continuous fold set along the side of the foot, known as the EPIPODIUM.

TENTACLE, LABIAL   = ORAL TENTACLE. See illustration: Composite Nudibranch.

TENTACLE, ORAL   [need definition]. In nudibranchs… ; = LABIAL TENTACLE. See illustration: Composite Nudibranch.

TENTACLE, PALLIAL   A tentacle, in rissoids and some other MESOGASTROPODS, growing from the edge of the mantle skirt on the right side and occasionally also on the left. In turritellids, a whole series of pallial tentacles lies around the entrance to the MANTLE CAVITY.

TENTACLES, METAPODIAL   One of two tentacular outgrowths (in the rissoids, lacunids, nassids, etc.) at the hind end of the FOOT or at the point where the OPERCULUM is attached.

TENTACULAR   Referring to the TENTACLES.

TENTACULAR SHIELD   [need definition]; present in the TECTIBRANCHS and CEPHALASPIDS.

TEREBRATING SHELLS   Those shells which bore into rock or wood; = BORERS.

TEREDINIFORM   A shape exemplified by the SHIPWORM bivalve genus Teredo. See other bivalve shapes.
Illustration: Teredo sp. (left = entire animal; center = PALLETS; right = shell)

TERMINAL AREAS   In CHITONS (the Polyplacophora), the HEAD VALVE and the radially sculptured posterior part of the TAIL VALVE.

TERRESTRIAL   Pertaining to or living on land; see also: ARBOREAL; HABITAT.

TERTIARY   Of the third order, generally said of sculpture; see also: PRIMARY; SECONDARY; QUARTERNARY. Also, the geological era extending from the Paleocene to the Pleistocene (about 60 million years duration).

TESSELLATE   Divided into squares; see also: CANCELLATE.

TEST   A SHELL; see also: CONCH.

TESTACEOUS   Shelly; bearing a shell or composed of shelly material; see also: TEST.

TESTE   In the testimony of; see also: AUCTT; IN LITT; PERS. COMM..

TETRABRANCH   Possessing four GILLS; that name applied to Nautilus (all other living cephalopods being DIBRANCHS); see also: BRANCH; DEMIBRANCH.



THECOSOMATA   The shelled PTEROPODS, generally held to be derived from bulloids... foot reduced, but the epipodia greatly expanded and used for swimming, gizzard armed with 4 plates, jaws and a small triserial radula present, only one genus (Peraclis) has a true gill, penis unarmed, all have CALCAREOUS shells, except for the Cymbulidae which have a TRANSPARENT PSEUDOCONCH; see also: GYMNOSOMATA.

THICKNESS   Used by some authors to denote the shell measurement termed INFLATION, but also commonly applied to the distance between the inner and outer surfaces of the wall of a shell.

THREAD   A very fine spiral sculptural element of a shell; see also: LIRA.

THREAD, SPIRAL   [need definition]. Finer than a SPIRAL GROOVE. See illustration: Composite Gastropod.

THREADED   SCULPTURED with many very fine spiral lines.

TIGHTLY COILED   Having many, narrowly expanding WHORLS; see also: LOOSELY COILED; IRREGULARLY COILED; SPIRALLY COILED. See other gastropod shapes.

TOOTH   A spur-like projection on the margin of a shell structure, more especially, an element of RADULAR dentition (in gastropods) or HINGE dentition (bivalves); see also: PARIETAL TOOTH; PALATAL TOOTH; TEETH.

TOPOTYPE   A specimen collected from the TYPE LOCALITY.

See the publication: "Terminology of Types" by Frizzell.

TORSION   The displacement of the MANTLE-and-shell from the enclosed VISCERAL MASS, rotating by growth stages in a flat or extended helix, and accompanied by the cessation of development of one-half of many of the paired organs in the soft parts; see also: DETORSION; GARSTANG'S THEORY.

TOXOGLOSSATE   A type of UNISERIATE RADULA, characteristic of the Conidae, resembling a harpoon tip and delivering a powerful venom (CONOTOXIN ). See also: RADULA FORMULA.

TRAILING EDGE   The hind portion of a structure, behind the leading edge; see also: LEADING EDGE.

TRANSLUCENT   Allowing light to pass through, but not undistorted images; see also: TRANSPARENT; DIAPHANOUS; PELLUCID.

TRANSPARENT   Allowing both light and undistorted (or nearly so) images to pass through; see also: TRANSLUCENT; DIAPHANOUS.


See: Van der Schalie, H. 1936. Transposed hinge teeth of North American naiades. Nautilus 49(3):79-84.

TRANSVERSE   Crossing the shell horizontally (i.e., spirally); see also: AXIAL; SPIRAL. In bivalves, the direction perpendicular to that of the CARDINAL AXIS in plane of valve margins; see also: CONCENTRIC; DIVARICATE.

TRAP DOOR   Common, non-technical name for the OPERCULUM.

TRAPEZIFORM   With four straight sides, only two of which are parallel; see also: POLYGONAL; QUADRATE.

TRAPEZOIDAL   With four straight unequal sides, no two of which are parallel; see also: POLYGONAL; QUADRATE.

TRIAD   A group of three (as in SPIRAL cords).

TRIANGULATE   Having three sides, as in the shape of a triangle; see also: TRIGONAL.

TRIDENTATE   Having three TEETH or points.

TRIGONAL   Having three sides and angles; triangular in outline; see also: TRIANGULATE; DELTOID; DONACIFORM. See other bivalve shapes.
Photo: Parastarte triquetra (Conrad, 1846)

TRIGONALLY SUBOVAL   Having features of being triangular and somewhat OVAL in shape. See other bivalve shapes.

TRILOBATE   Having three lobes or parts; see also: BILOBATE; LOBATE.

TRIPARTITE   Having three parts; see also: BIPARTITE.

TRIPTEROUS   Three-winged; generally meaning TRIVARICATE with ALATE VARICES.

  Having two projecting parts or branches. See also: Having projecting parts or branches. See also: RAMOSE; BIRAMOSE.

TRIVARICATE   Having three VARICES for each full turn of a WHORL.

  Having the form of a top; conical, with the base of the cone at the APERTURE; see also: TURBINATE. See other gastropod shapes.

TROCHOPHORE   The first LARVAL stage of molluscs, it is followed in gastropods and bivalves by the VELIGER stage.

TRUNCATE   Terminating bluntly; see also: DECOLLATE.

TUBE   A long, slender, hollow structure.

TUBERCLE   A small, rounded projection; a knob.


TUBULAR   Cylindrical, (pertaining to the gastropod families Caecidae, Vermetidae, etc.), often used to mean open at both ends (as in the scaphopods, or TUSK SHELLS). See other gastropod shapes.


TUNNEL   A tube; generally said of subsurface structures in the INTRITICALYX of ASPELLOID species.

TURBINATE   Having a broadly conical spire and a convex base, as in the gastropod family Turbinidae; see also: TROCHOID. See other gastropod shapes.

TURGID   Swollen, enlarged, puffed up or distended; strongly inflated; = VENTRICOSE; = TUMID; see also: INFLATED; SWOLLEN.

TURRETED   Having a tall and generally tabulate SPIRE; having the tops of the whorls flattened.

TURRICULATE   Having the form of a tower; = TURRIFORM. See other gastropod shapes.

TURRID NOTCH   An ANAL NOTCH, or a break in the wall of the outer lip where it joins the BODY WHORL; see also: STROMBOID NOTCH.
Photo: Pyrgocythara plicosa (C.B. Adams, 1850)

TURRIFORM   Tower-shaped; = TURRICULATE. See other gastropod shapes.



TYPE DEPOSITORY   The scientific collection in which a TYPE SPECIMEN is deposited.

TYPE LOCALITY   The geographical area from which TYPE MATERIAL was originally collected and which was cited as such by the author.

TYPE MATERIAL   [need definition].

See the publication: Frizzell, Donald Leslie. 1933. Terminology of Types. American Midland Naturalist 14(6):637-668.