Dreissena polymorpha

The prominent dark and light banding pattern on the shell is the most obvious characteristic of D. polymorpha. Its specific name, "polymorpha", derives from its many variations in shell colour, pattern and shell shape. The outer covering of the shell (the periostracum) is generally well polished, and light tan in colour with a distinct series of broad, dark, transverse colour bands which may be either smooth or zigzag in shape. Within a population, individual shell colours may range from very light coloured without discernable dark banding to those that are darkly-pigmented overall, obliterating all banding.