Zebra mussel

The zebra mussel (Dreissena polymorpha) is a small freshwater mussel, an aquatic bivalve mollusc in the family Dreissenidae. The species originates from the lakes of southwestern Russia and southeastern Europe, but has been accidentally introduced to numerous other areas and has become an invasive species in many countries in the Northern Hemisphere. Since the 1980s, the species has invaded the Great Lakes, Hudson River, Lake Travis, Finger Lakes, Lake Bonaparte, and Lake Simcoe. The adverse effects of dreissenid mussels on freshwater systems have led to their classification as among the world's most invasive aquatic species. The species was first described in 1768 by German zoologist Peter Simon Pallas in the Ural, Volga, and Dnieper Rivers. Zebra mussels get their name from a striped pattern commonly seen on their shells, though it is not universally present. They are usually about the size of a fingernail, but can grow to a maximum length around 50 mm (2 in). Their shells are D-shaped, and attached to the substrate with strong byssal fibres, which come out of their umbo on the dorsal (hinged) side.