Valve (mollusc)

A valve is each articulating part of the shell of a mollusc or another multi-shelled animal such as brachiopods and some crustaceans.

Thus individual plates can be found washed up in beach drift, as shown in the image at the top of this article.

Bivalve molluscs (e.g. clams and oysters) have a shell which is composed of two separate but articulating parts.

In contrast, species within one family of small sea snails, the Juliidae, opisthobranch gastropod molluscs, have a hinged shell which is composed of two parts joined by a ligament.

This distinguishes their valves from those of actual bivalves, which form an identical, but mirrored structure as they are derived from the side of the body.