The internal structure of the mussels in the coat cavity on each side of the mussel body with two pieces of gills, the outer gills shorter than the inner gills. Each gill is composed of two gill flaps inside and outside, the front and back edges and the ventral edge of the fusion into a "U" shape, the dorsal edge of the upper gill cavity. Gill flap consists of many longitudinal arrangement of gill filaments, the surface of the cilia, the gill filaments are connected to the transverse arrangement of the filament spacer, gill filaments and the filament spacer between the small holes called gill holes. Between the two gill flaps there are flap intervals, the gill cavity between the gill flaps is separated into many small tubes called gill water tubes. There are blood vessels in both the filamentous intervals and the flap intervals, and there are also blood vessels in the gill filaments as well as several plasmodial rods that play a supportive role. Because of the gills and the outer coat membrane cilia swing, cause water flow, water from the water hole into the outer coat cavity, through the gill water hole to the gill water tube, along the water tube up to the upper gill cavity, backward flow, through the outlet pipe out of the body.
When water passes through the gills, gas exchange takes place. The outer membrane also has the function of assisted respiration. Every 24 hours through the mussel body of water up to 40L, gill surface cilia can filter food particles in the water, sent to the lips and then inlet. Therefore, the gills can still assist in feeding. By the heart, blood vessels, blood sinuses. The heart is located in the dorsal oval pericardial cavity of the visceral mass, consisting of an oblong ventricle and two thin films of triangular auricles on the left and right. The ventricle extends anteriorly and posteriorly with one large artery each. The anterior aorta extends forward along the dorsal side of the intestine, the posterior aorta extends posteriorly along the ventral side of the rectum, and later branches into small arteries to the coats and all parts of the body. Finally, they converge in the blood sinuses (coat sinus, pedunculated sinus, central sinus, etc.), enter the veins, enter the kidneys through the renal veins to eliminate metabolites, then enter the gills through the gill veins to carry out oxygen-carbon exchange, and return to the heart ear through the gill veins. Part of the blood enters the cardiac auricle by the socket vein, i.e., the coat circulation. The blood of toothless mussels contains hemocyanin, which is blue when oxidized and colorless when reduced, and its ability to combine with oxygen is not as good as that of hemoglobin, and the oxygen content of 100 ml of blood in general mollusks is usually not more than 3 mg.
The blood contains amoeboid cells, which have phagocytosis effect. Therefore, in addition to transporting nutrients, blood also has the function of excretion. Amoeboid cells aggregate and their pseudopods partially bind to each other, causing the blood to coagulate (there is no fibrinogen in clam blood). Toothless mussels have three pairs of ganglia. Below the anterior closed-shell muscle, on both sides of the esophagus is a pair of cerebral ganglia, which are very small and are actually formed by the merger of cerebral ganglia and lateral ganglia, and can be called lateral cerebral ganglia. In the anterior edge of the foot against the upper buried in the foot for a pair of long foot ganglia, the two combined together. The dirty ganglion is a pair of healed, butterfly-shaped ganglia, located under the epithelium of the ventral aspect of the posterior closed shell muscle, and is larger. The three pairs of brain, foot and dirty ganglia are connected by nerve cords, and the brain and dirty nerve cords are longer. The senses of the mussel are not developed, and there is a balance capsule near the peduncle ganglion, which is formed by subsidence of the peduncle epithelium. There is an otolith inside, which is responsible for the balance of the body. The epithelium above the visceral ganglion becomes the sensory epithelium, which is equivalent to the olfactory detector of gastropods and is a chemoreceptor. In addition there is a distribution of sensory cells in the outer coat membrane and around the labial lamellae and water tubes.
The internal structure of mussels above is the principle of the internal structure of mussels, from which we can know that mussels are omnivorous, like worms, green algae are its food, relying on the action of the water to send food into the body, with the seasonal variations have great changes.