Shellfish morphology and structure 2

The digestive system includes the mouth, tooth tongue esophagus, gastrointestinal tract, anus, and accessory digestive glands. Among them, tooth tongue is a special organ for shellfish to eat and grind food, and it is one of the important basis for classification.

Shellfish breathe by gills and lungs. The aquatic species have gills, which are usually formed by stretching the skin on the inner surface of the mantle and are called native gills. Each gill piece has gill filaments on both sides or one side of the gill shaft, and cilia grow on the gills. According to the movement of the cilia, the breathing water flows through the gills for gas exchange in a certain line. In some species, the original gills disappear, and the skin surface or secondary gills (posterior gills) are formed on the skin surface to breathe. Part of the mantle of the terrestrial species forms a densely veined pulmonary chamber for breathing in the air.

The circulatory system is generally open-tube type, but in advanced cephalopod arterial and venous tubes are connected by capillaries to become closed-tube types. The center of the circulatory system of shellfish is the heart. The heart has 1 ventricle and 1, 2 or 4 auricles. The blood contains hemocyanin and is generally colorless. Only a few species, such as cockles of bivalves and snails of gastropod, have heme, and blood is red.