|Live zebra mussels underwater with shells open, animals
respiring, siphons visible| The zebra mussel, Dreissena
polymorpha, is a small freshwater mussel. This species was
originally native to the streams of southern Russia being first
described in 1769 by a German zoologist Peter Simon Pallas in
the Ural, Volga and Dnieper rivers. They are still found nearby,
as Pontic (Black Sea) and Caspian (Caspian Sea) species.
However, it has been accidentally introduced in many other
areas, and has become an invasive species in many different
countries worldwide. Zebra mussels superficially resemble marine
mussels in the family Mytilidae, and like them, are attached to
solid substrates with a byssus. However, zebra mussels are not
at all closely related to the mytilids; they are much more
closely related to the Veneridae, the Venus clams. Zebra mussels
get their name from a striped pattern which is commonly seen on
their shells, though not all shells bear this pattern. They are
usually about the size of a fingernail, b