Mussel, << MUHS uhl, >> is a water animal protected by a hard shell. Mussels live in oceans and in fresh water. Their shell consists of two plates called valves, which are joined by a hinge. Large adductor muscles close the shell tight in case of danger.
Marine mussels usually live in shallow waters along ocean coasts. They attach themselves to rocks by producing strong, sticky byssal threads made of protein. Marine mussels form large populations that carpet vast areas. They feed on tiny plantlike organisms called plankton, which they trap in their gills. Several marine mussels are eaten by people. One such variety, the blue mussel, has a shell that is bluish-black on the outside. It can grow to about 4 inches (10 centimeters) long.
Freshwater mussels are only distantly related to marine mussels. They often live buried in sandy bottoms of rivers, streams, and lakes. Freshwater mussels were once a major source of mother-of-pearl, a rainbow-colored material that lines their shells. Mother-of-pearl is often used in jewelry. Because of over-harvesting and damage to their habitat, many freshwater mussels are in danger of becoming extinct.
