Sculpture (mollusc)

Sculpture is a feature found in the shells of gastropods, bivalves, and scaphopods.

The word "sculpture" is also applied to surface features of the aptychus of ammonites, and to the outer surface of some calcareous opercula of marine gastropods such as some species in the family Trochidae.

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.

The shell of the sea snail Epitonium scalare has a sculpture of sharp vertical ribs known as "costae"
The shell of the freshwater snail Bulinus forskalii has strong transverse ribs which form an angle at the shoulder