Oyster

Oyster. The two hard, rough-textured shells are attached by a muscular hinge (the adductor muscles) at the narrow end. The shell is generated by the mantle, a thin layer of tissue separating the shell from the soft body. When an oyster is threatened, it closes its shells, using the very strong adductor muscle. Oysters are soft-bodied animals that have two hard, protective shells (a bivalve). They spend their entire lives in one underwater location. The shape of the oyster`s shells varies, depending mostly upon how crowded they are in the oyster bed. Oysters draw in water through their gills, and extract oxygen and filter out floating algae (which they use for food). An oyster changes its sex during its life; it starts out as a male and often ends as a female. The largest oysters are up to 3 feet (1 m) long, but most are a few inches long.