Sphaeriidae
Fingernail Clams, Pea Clams
Fingernail clams, also called pea clams, are members of a family of small to tiny freshwater clams that are common but rarely noticed. Like other clams, they have two mirror-image shells that are hinged together, and the shells are generally rounded to triangular. In fingernail clams, the shells are thin and fragile, often translucent, the outsides typically shiny, fairly smooth, and gray, tan, yellowish, or whitish. Fine growth lines are often visible, but they are not strongly raised, ridged, or rough.
Invasive species of Asian clam (Corbicula spp.), zebra "mussel" (Dreissena polymorpha), and quagga "mussel" (Dreissena bugensis) are nuisances for humans and native bivalves including native pea clams and fingernail clams.