Shell size to 18 mm; shell mussel-shaped, mildly elongate, ventral region concave, anterior end forming sharp beak. Umbones subterminal. Hinge with v-like depression on shelf under beak shelf and corresponding tooth on opposite valve. Exterior color variable, usually light bluish-brown to whitish-cream, sometimes found with thin, tan periostracum. Interior bluish to tan. Found attached to hard substrates by byssus, forming mussel-like clumps or nestling in crevices. Belongs to same family as the zebra mussel Dreissena polymorpha. A brackish water species found in estuaries, coastal lakes, and ponds.