It should be oysters. Is the oyster "yes"? Oysters? Synonym for ". Since 2000 BC, oysters have been cultivated as food; Pearls can be produced in the shell of pearl oyster. The two shells of oysters are different in shape, and the surface is rough and dark gray; The middle part of the upper shell protrudes; The lower shell is attached to other objects, with large volume, quite flat and smooth edges; The inner surfaces of both shells are white and smooth. The two shells are connected at the narrower end by an elastic ligament. There is a powerful adductor muscle in the middle of the shell to resist the tension of the ligament. When the shell is slightly opened, water is introduced into the shell through the wavy motion of cilia (the water flowing through it can reach 2-3 gallons per hour) to filter microorganisms. Birds, starfish, snails and fish including rays all eat oysters. Oysters and snails are widely distributed. It often drills a small hole in the oyster shell with its tongue and sucks its living tissue. Oysters are mostly hermaphroditic, but some are hermaphroditic. Edible oysters (Ostrea edulis) can change their sex according to the season or with the change of water temperature (rhythmic hermaphroditism). Oysters breed in summer. Some kinds of eggs are fertilized in water, while others are fertilized in females. The hatched larvae are spherical and ciliated, and are permanently fixed to other objects after swimming for several days. Harvest after 3 ~ 5 years.