Valve (mollusc)
This article needs additional citations for verification. (August 2014) |
![](http://upload.wikimedia.org/wikipedia/commons/thumb/9/91/Chiton_tuberculatus_plates.jpg/100px-Chiton_tuberculatus_plates.jpg)
A valve is each articulating part of the shell of a
Species within one family of very unusual small
Chitons
![](http://upload.wikimedia.org/wikipedia/commons/thumb/5/54/Tonicella_lineata_1.jpg/220px-Tonicella_lineata_1.jpg)
The valves of
Bivalves
![](http://upload.wikimedia.org/wikipedia/commons/thumb/1/1f/Abra_alba_2.jpg/220px-Abra_alba_2.jpg)
The two valves are known as the "right valve" and the "left valve"; these are labeled with respect to the anterior end of the bivalve, when the umbones are facing upward. In many, but not all, bivalves, the two valves are more or less symmetrical and thus (other than the hinge line) look like mirror images of one another.
Bivalved gastropods
![](http://upload.wikimedia.org/wikipedia/commons/f/fd/Juliidae.png)
The great majority of shelled
In contrast, species within one family of small
![](http://upload.wikimedia.org/wikipedia/commons/thumb/a/a2/Julia_borbonica_shell_2.jpg/220px-Julia_borbonica_shell_2.jpg)
These bivalve gastropods were for a long time known only from fossils and dead material. Because of this, they had been described as being somewhat atypical bivalves. It was not until living individuals were found in the late 20th century that it was understood that these are in fact very unusual gastropods.
Other animals
Valves are present in any animal with two or more shell portions connecting at a hinge. Brachiopods are bivalved animals with two valves stacked vertically (rather than laterally). The dorsal, or brachial valve hosts the brachial system which supports feeding structures, while the rear end of the ventral, or pedicle valve sends out a fleshy holdfast known as a pedicle. Though each valve has its own symmetrical structure, the two valves have different overall forms and are not mirror images of each other. 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.
Some