The abductor muscles and a ligament work to open and close a bivalve. The abductor muscles contract to close the shell, while the ligament forces the shell open. This muscle and ligament activity enables bivalves, such as clams, scallops and oysters, to open and close their shells.
Most bivalves obtain nutrition by filtering water through their bodies and extracting organic material to eat. This water comes in through a bivalve's gills, which also draw in oxygen. Some bivalves also eat sediment, or dirt, to ingest nutrition instead of filtering water. Opening and closing a bivalve's shell is critical to these processes.