The Class Bivalvia consists of organisms known as Bivalves. These are molluscs that have shells divided into two jointed halves called valves. This class includes clams, oysters, mussels, scallops, and shipworms. They range largely in size from 1 millimeter clams to others that grow as large as 1 meter. Some bivalves burrow in sand for protection. This way, they feed on food suspended in water but a problem is that sand is often brought in with the water currents. However, some species have siphons that project above the surface of the sand that allows for them to remain completely burrowed while also getting food. Other bivalves are attached surface dwellers such as mussle and others still are unattached, such as scallops. A few bivalves, like shipworms, burrow in wood or stone.