(phylum Mollusca, class Bivalvia)
A subclass of bivalves most of which have thin, equivalve shells composed of aragonite. They have an amphidetic to opisthodetic external ligament. The hinge plate is narrow or absent, with most forms having an edentulous hinge margin; some members are taxodont. They have an infaunal mode of life. They first appeared in the Ordovician.
Subjects: Zoology and Animal Sciences — Earth Sciences and Geography.