The New Student's Reference Work/Clam
Clam, the name applied to the freshwater mussel and similar animals living in salt water. They have bivalve shells, held closed by muscles and open by a springy ligament on the back of the shell; therefore, the shell of a dead clam always stands open. They creep through the mud and sand of the bottom by means of a fleshy foot. A current of water is drawn through a tube and is strained through the plate-like gills; it then passes into a chamber in the body and out by another tube. The food consists of minute animals and organic matter in the water. This is separated by straining the water through the gills, and is carried to the mouth by the movement of small hair-like projections or cilia. The shell is secreted by glands in the mouth, which covers the body, and is enlarged by rings as the animal grows.