Sculpture (mollusc)

Sculpture on a mollusc shell is whatever natural 3-dimensional ornamentation exists on the outer surface of a shell, apart from the basic shape of the shell itself. The term sculpture is most often applied to the shells of gastropods and bivalves, and to a lesser extent to scaphopods and polyplacophorans.

The word sculpture is usually applied to the calcareous outer layer of the shell, not the periostracum of the shell, which may sometimes be textured even when the underlying layer of shell is smooth.

In many species or families, the shells have no sculpture apart from fine growth lines, but when a more distinctive sculpture does exist, it is sometimes very useful in discriminating one species from another. In some cases the sculpture is so fine-textured that it has to be examined under the microscope.

Sculpture may protrude from the overall surface of the shell or be incised into it. Incised sculpture can consist of incised lines, grooves, punctures, etc. Sculpture which protrudes from the surface of the shell may consist of ribs, nodules, and so on.

A list of terms describing the sculpture of a molluscan shell

*Axial sculpture - Sculpture running parallel to the axis of coiling. The Axis is an imaginary line through the apex of a gastropod shell, about which the whorls are coiled.
*Bead - A small hemispherical protuberance resembling a bead, similar to but smaller than a nodule.
*Beaded resembling rows or strings of beads.
*Growth Line(s) - fine transverse lines marking growth of the shell.
*Lirate - ornamented with fine thread-like lines or grooves.
*Longitudinal sculpture - following the direction of the axis of the shell.
*Nodule - A rounded protuberance on the shell sculpture; larger than a bead.
*Nodose, Nodulose or Nodular - bearing small rounded protuberances or tubercules.
*Ornament - Can refer to surface sculpture standing out in relief on shell surface; or simply to sculpture as a whole.
*Pustule(s) - very fine knob-like protrusions, smaller than a tubercule.
*Reticulate - sculpture consisting of a criss-crossing network of riblets, threads, or grooves.
*Rib - a strong ridge on the surface of the shell.
*Riblet - smaller than a rib, but coarser than a thread.
*Spiral sculpture - Sculpture following the spiral growth of the shell.
*Stria (Pl. "striae") - a shallow incised groove.
*Striate - ornamented with striae.
*Thread - a very fine riblet.
*Transverse sculpture - sculpture parallel to the edge of the outer lip of the aperture.
*Tubercle(s) - Elevated knob-like projections or protrusions; larger than pustule.
*Varicose - Bearing a varix or varices.