Sculpture can be concave or convex, incised into the surface or raised from it. Sometimes the sculpture has microscopic detailing. The term "sculpture" refers only to the calcareous outer layer of shell, and does not include the proteinaceous periostracum, which is in some cases textured even when the underlying shell surface is smooth.
In many taxa, there is no sculpture on the shell surface at all, apart from the presence of fine growth lines.
The sculpture has a protective function because it increases the diameter of the shell, distributing mechanical stress (such as the force of a predator's jaws) across a larger surface area.
List of terms
Axial sculpture - Sculpture running parallel to the axis of coiling, an imaginary line through the apex of a 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 - A fine transverse line marking the growth of the shell.
Lira, lirate - ornamented with fine thread-like lines or grooves.
Longitudinal sculpture - Sculpture following the direction of the axis of the shell.
Nodule - A rounded protuberance on the shell sculpture; larger than a bead.
Nodose, Nodulose, 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.
^Ward, Peter (1981). "Shell Sculpture as a Defensive Adaptation in Ammonoids". Paleobiology. Cambridge University Press. 7 (1). Retrieved 21 November 2020.
^Palmer, A. Richard (June 1979). "Fish Predation and the Evolution of Gastropod Shell Sculpture: Experimental and Geographic Evidence". Evolution. Society for the Study of Evolution. 33 (2): 697–713. doi:10.2307/2407792. Retrieved 21 November 2020.