Mussels and clams (Bivalia) are molluscs with two shells.
There are two major groups (Orders) of the Bivalia, Veneroida (the clams and pseudo-mussels) and Unionida (true mussels).
There are 4 families containing 42 genera and at least 65 species in Ohio. Two of these families are introduced species, Corbiculidae (the asian clam) and Dreisseniidae (zebra mussles). The large majority of this group are in the family Unionidae.
They range in tolerance to pollution from sensitive to tolerant. Several are endangered, threatened and of special interest.