These bivalves are distinguished by having the two halves of the shell equally sized (i.e, they are equivalved), and having a few cardinal teeth separated from a number of long lateral teeth. Their shells lack a nacreous layer, and the gills are lamellibranch in form. Most species have a siphon.
In 2010, a new proposed classification system for the Bivalvia was published in by Bieler, Carter & Coan, revising the classification of the Bivalvia, including the subclass Heterodonta.
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