Olympia oyster

This bivalve is approximately 6 to 8 centimetres (2.4 to 3.1 in) in length. The shell can be rounded or elongated and is white to purplish black and may be striped with yellow or brown. Unlike most bivalves, the Olympia oyster's shell lacks the periostracum, which is the outermost coating of shell that prevents erosion of the underlying shell. The color of the oyster's flesh is white to a light olive green. Ostrea lurida oysters lie with their left valve on the substrate, where they are firmly attached. Unlike most bivalves, oysters do not have a foot in adulthood; they also lack an anterior adductor muscle and do not secrete byssal threads, like mussels do. Olympia oysters are suspension feeders, meaning they filter their surrounding water and screen out the phytoplankton they feed on. Olympia oysters filter between 9 and 12 quarts of water each day, but is highly dependent on environmental conditions. This is an essential function to keeping marine waters clean. Oyster beds also provide shelter for anemones, crabs, and other small marine life.