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Clam (alias: clam), an animal of the order Macidae. It is distributed in all oceans of the world. The shells are of equal size, triangular or oval, usually thin, often with a shell skin, the shell surface is smooth or has concentric growth lines, the inner edge of the shell is flat and sharp, the top of the shell is mostly protruding and tilted forward; the edge of the top of the shell is There is an external ligament, the top is usually healed, and the left and right shells have lateral teeth, single on the left and double on the right. It mostly inhabits the middle and lower areas of the intertidal zone and the shallow seabed within 100 meters of the subtidal zone. A few can live in the deep sea above 100 meters and live in caves.

The shells are uniform in size, triangular or oval in shape, and most species have unequal sides. Shells are usually thin, some species have two shells closed, and most species have one or both ends open, often with a shell skin; the shell surface is smooth or has concentric growth lines, and the inner edge of the shell is flat and sharp. The top of the shell is mostly prominent and tilted forward. There is usually a clear boundary between the lunar surface and the lunar surface. There is an outer ligament on the top edge of the shell, and a ligament groove in which the inner ligament is located. The left shell of the hinge has a split main tooth, inverted "V" shape, the top is usually healed, and the rear branch of the main tooth is next to an accessory piece; the main tooth of the right shell is usually separated. Both the left and right shells have side teeth, the left shell has a single tooth and the right shell has double teeth. Mantle sinuses are usually deep, rounded or angular, with long aqueducts that heal at the ends.

Oyster, an animal of the family Oysteridae. It is the largest cultivated shellfish in the world and one of the important marine biological resources available to humans.

The shell of an oyster can be divided into three layers in cross-section: the outermost layer is the thin and transparent cuticle, the thickest middle layer is a columnar structure composed of calcium carbonate called the prism layer, and the inner layer is calcium carbonate. The flaky structure is called nacre. Oysters are found throughout the world.

The shell can be divided into three layers on the cross section; the outermost layer is the thin and transparent cuticle, the middle layer is the thickest columnar structure called prism layer composed of calcium carbonate, and the inner layer is the sheet of calcium carbonate. Like structure, called nacre. The shell is secreted by the mantle below. The mantle extends from the top of the shell to the ventral edge. It is two layers of epithelial cells with a membrane formed by connective tissue in the middle. There are muscle fibers in the membrane to attach it to the inner surface of the shell. The mantle The edge of the membrane is thickened to form three folds, and there are radial muscles and circular muscles on the inner folds to keep the edges close to the shell. There are a large number of sensory cells or receptors on the middle fold, which have functions such as touch and vision. The outer folds have a strong secretory function.

The two shells are unequal. The left shell, or lower shell, is larger and concave. The left shell is fixed on rocks or wooden piles on the seabed. Generally, in the later stage of metamorphosis of the facial disc larvae, mucus is secreted by the byssal threads to fix the edge of the mantle to the substrate, and then the shell secreted by the mantle directly adheres to the plug. The foot has completely disappeared, the anterior adductor muscle has also degenerated and disappeared, and the posterior adductor muscle has moved to the middle of the body, completely losing the ability to move. The adductor muscle and ligament have antagonistic effects. Due to the permanent sessile life, developed small tentacles or sense organs appear on the edge of the mantle. The mantle never develops healing points or forms water tubes because they live on hard surfaces where there is rarely a large amount of sediment due to tidal movements. It has had a clearing effect.