Bivalves are molluscs with bodies that are enclosed in a shell of two halves (valves) that can be opened at one end. The animal pumps water in and out of the shell. This water brings dissolved oxygen for the animal to breathe with gills and, in most species, food particles. Bivalves can be found in fresh water or saltwater environments. Edible shellfish, including oysters, mussels, steamer clams and scallops, are bivalves.