Clams, mussels, pipis and oysters - Class Bivalvia
Bivalves are molluscs, well-known to humans who have developed a taste for many of them. This group includes oysters, mussels, pipis, cockles, scallops and clams.
The name bivalve means 'two valves'. The soft-bodied animals live inside the shell valves, which are joined together by a toothed hinge and a flexible ligament. When the animal inside dies, the ligament usually breaks and the shells are found washed up on the beach.
Bivalve molluscs are found in aquatic environments, with the majority (about 80%) being marine species. In general, bivalves are filter feeders, passing water through their gills to extract organic food particles known as plankton.
Bivalves tend not to be very mobile, settling in the one place as adults. Some attach themselves to hard surfaces using tough 'byssal threads', some burrow into the sand, and others, like oysters, cement themselves to a rock surface.