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.

Loose shell plates or valves of Chiton tuberculatus from the beach drift
Live individual of the lined chiton Tonicella lineata , head end towards the right
Paired valves of the bivalve Abra alba
A live individual of an unidentified species of bivalved gastropod in the family Juliidae
Drawing of the interior of the left valve of the shell of " Julia borbonica "