Chama

Chama, a genus of bivalve molluscs, the only surviving type of a family which was once extremely numerous and abundant, especially in the Jurassic and Chalk times. The genus is represented by about half a hundred living forms, restricted to warmer waters, and especially common about coral reefs. The general appearance is somewhat clam-like, the valves are unequal, of considerable thickness, and covered with leaf or scale-like outgrowths. They are very passive animals, usually fixed, with the mantle margins fused together, with very small foot and respiratory apertures, with well-developed hinge and an external ligament, and often of a bright colour. Some forty fossil species are known from Cretaceous and Tertiary strata, and the genus is of interest as the sole survivor of a once much larger family. The common English name for shells of the genus is Clam (q.v.).