Oyster shells can be divided into three layers in section; The outermost layer is a thin and transparent stratum corneum, the thickest layer is a columnar structure composed of calcium carbonate called prismatic layer, and the inner layer is a flaky structure called nacre.

The shell is formed by the secretion of the lower mantle, which extends from the top of the shell to the edge of the abdomen. It is a membrane formed by two layers of epithelial cells with connective tissue between them. There are muscle fibers in the membrane that make it adhere to the inner surface of the shell. The edge of the mantle thickens to form three folds, and there are radial muscles and annular muscles on the inner folds to make the edge close to the shell. There are a large number of sensory cells or organs in the folds, which have tactile and visual functions. The outer fold has a strong secretory function.

The two shells are unequal, the left shell or the lower shell is large and concave, and the left shell is fixed on rocks or seabed stakes. Generally, in the later stage of metamorphosis, the foot silk secretes mucus, which fixes the edge of the mantle on the substrate, and then the shell secreted by the mantle directly adheres to the plug.

The foot completely disappeared, the degeneration of the adductor muscle disappeared, and the adductor muscle moved to the middle of the body, completely losing its mobility. Adductor muscle and ligament have antagonistic effect. Due to permanent fixation, there are developed small tentacles or feelings at the edge of the mantle. Mantles never have healing points or water pipes, because they live on hard surfaces, where there are almost no sediments, which have been carried away by tidal movements.

Oysters usually ripen within a year. In the first year, they lay eggs like males and release sperm into the water. As they grow up and produce more energy reserves in the next two or three years, they will lay eggs in the form of females by releasing eggs. Bay oysters usually lay eggs from late June to mid-August.

habitat

As a key species, oysters provide habitats for many marine species. ? Oysters and monk's hats mainly live in intertidal zone, while oysters live in subtidal zone. The hard surface of oyster shells and the corners between them provide a place for many small animals to live. Hundreds of animals, such as anemones, barnacles and mussels, inhabit oyster reefs. Many of these animals are prey of large animals, including fish, such as striped bass, black drum fish and yellow croaker.

Oyster reef can increase the surface area of flat bottom by 50 times. The mature shape of an oyster usually depends on the type of bottom it is originally attached to, but it always locates itself with its open shell tilted upward. One valve is cup-shaped and the other is flat.