| Term | Definition |
| DIRECTIVE SPIRAL | Spiral curve formed by DIRECTIVE RIB within its own plane. | |
| 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. | |
| MULTISPIRAL | Consisting of whorls of uniform width, as in the OPERCULUM of Batillaria spp.; = OPERCULUM, ANNULATE. See also: PAUCISPIRAL; CONCENTRIC. | |
| OPERCULUM, MULTISPIRAL |
An OPERCULUM consisting of radiating WHORLS of uniform width; = OPERCULUM, ANNULATE; = POLYGYROUS SPIRAL. For illustrations, see The Humble Operculum website page: Operculum Structures. |
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| 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. |
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| PAUCISPIRAL | Having only a few WHORLS or turns, of increasing width; see also: MULTISPIRAL; PLANISPIRAL; CONCENTRIC. | |
| PLANISPIRAL | Coiled in a single plane; loosely used also with DISCOIDAL shells having asymmetrical sides; see also: MULTISPIRAL; LENTICULAR. See other gastropod shapes. | |
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| POLYGYROUS SPIRAL | See: OPERCULUM, MULTISPIRAL. | |
| 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). |
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| SPIRAL SCULPTURE | Sculpture following the HELICAL growth of the gastropod shell. | |
| SPIRALLY COILED | See: HELICAL. See also: IRREGULARLY COILED; LOOSELY COILED; TIGHTLY COILED. | |
| STRIA, SPIRAL | [need definition]. See also: CORD. See illustration: Composite Gastropod. | |
| SUBSPIRAL | Not sufficiently SPIRAL to form a complete VOLUTION. | |
| THREAD, SPIRAL | [need definition]. Finer than a SPIRAL GROOVE. See illustration: Composite Gastropod. | |