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

by Paul S. Mikkelsen

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Term Definition

ACCESSORY VALVE   See: ACCESSORY PLATE.
   

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.
   

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

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

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

See illustration: Composite Chiton.
   

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.
   

LEFT VALVE
(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.
   

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

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

See illustration: Composite Chiton.
   

RIGHT VALVE
(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.
   

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

See illustration: Composite Chiton.
   

UNIVALVE   A shell consisting of a single piece, as in most GASTROPODS; see also: BIVALVE.
   

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

VALVE   One of the shelly halves of a clam (or BIVALVE) shell, or the single shell of a GASTROPOD (UNIVALVE), or one of the 8 (typically) shelly plates of a CHITON. See illustration: Composite Chiton.
   

VALVE CALLUS   Same as: INSERTION PLATE.
   

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

VALVE, CENTRAL AREA   [need definition]. In CHITONS, See illustration: Composite Chiton.
   

VALVE, LATERAL AREA   [need definition]. In CHITONS, See illustration: Composite Chiton.
   


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