Zebra Mussels

Zebra mussels are relatively small, with adults ranging from 0.25 to 1.5 in (0.63 to 3.8 cm) long. They have tiny stripes down their shells. Zebra Mussels have a D-shaped shell. They attach to things with 'strings', byssal threads, which come out of their umbo on the dorsal (hinged) side. Removal of the mussel is therefore difficult.
Zebra mussels attach to most substrates including sand, silt, and harder substrates. Other mussel species frequently represent the most stable objects in silty substrates, and zebra mussels attach to, and often kill these mussels