Bivalvia, common name the bivalves, is a taxonomic class of marine and freshwater molluscs that have a laterally compressed body enclosed by a shell in two hinged parts. This class includes the clams, oysters, mussels, scallops and numerous other families. The majority are filter feeders and have no head or radula. The gillshave been modified into ctenidia, specialised organs for feeding and breathing. The majority of bivalves are infaunal and bury themselves in sediment on the seabed. Others are epifaunal and attach themselves to hard surfaces. A few bore into wood, clay or rock and live inside these substances. Some bivalves, such as the scallops, can swim.