Before the mouth position is closed, it is a transverse seam under the muscle. There are a pair of triangular lips on both sides of the mouth, which are large and dense and have the functions of feeling and eating. Behind the mouth is a short and wide esophagus connected with an enlarged stomach. There are a pair of livers around the stomach, which can secrete amylase and sucrase, and a catheter enters the stomach. Behind the stomach is the intestine, which is coiled in the visceral mass and then shortlisted for the heart. The rectum passes through the ventricle, and the anus opens on the posterior obturator internus near the outlet pipe. There is a crystal rod between the gastrointestinal tract, which is a slender rod with a thick front end and a large morphological variation at the top end, which is slender, swollen, hooked and coiled. The crystal rod is located in the intestine, and its front end protrudes out of the stomach and is connected with the lower part of the gastric shield. Crystal stems can store food. In the absence of food, the crystal stem disappeared after 24 hours and was fed again. A few days later, the crystal stem recovered. Mytilus feed on organic particles, rotifers, flagellates, algae and small crustaceans.
Anodonta
Lamellbranchia is the general name for the toothgill shellfish. Distributed in Asia, Europe, North America and North Africa.
Mussels are oval and oval. The shell is thin and fragile. The two shells are spread out, and sometimes there is a tail on the back. The top of the shell is broad and slightly convex, located in the middle or front of the trailing edge. The shell surface is smooth, with concentric growth lines or green radiation from the top of the shell to the abdominal edge. The gluing part is narrow and toothless. The shaft and feet are developed. Dioecious. Eggs are fertilized in spring and can develop into hookworm larvae in about 2 months, which are excreted. If the egg is fertilized in autumn, the embryo overwinters in the mother and develops into hookworm larvae in the next spring. After the hookworm larvae are excreted, they will inevitably parasitize the fish. When they develop into young mussels, they will leave the fish, sink to the bottom and live freely. Meat is edible, and it is also the natural bait for fish and poultry, and the feed for livestock and poultry. Some varieties can be used as freshwater pearls.
A.woodiana woodiana is a common species in China. Its shell is 200mm long, oval, with horny protrusions, two swollen shells, wings at the back of the back edge, three rib veins on the back, and the lowest rib vein is located at the center line of the shell. Most of them live in mud bottom, slow flow and still water area, and are distributed in rivers, lakes, reservoirs and ponds. Dioecious. In Jiangsu province, the gonads mature in March, and the mature eggs are fertilized and developed in the female external gills. From April to May, hookworm larvae mature and excrete, parasitize on fish, develop into young mussels and then sink into the bottom of the water to live. Pearl mussels are cultured in fresh water, but the production quality of pearls is poor. Meat is for eating. Shells are Chinese herbal medicines.
appearance
The toothless mussel has two oval shells, which are isomorphic left and right, and the shell items are prominent. The front end of the shell is round, the back end is slightly cross-sectional, the belly line is curved, and the back line is straight. The twisted part has no teeth, and there are ligaments outside. Because of its elasticity, the two shells can be opened. The growth line on the shell surface is obvious.
Muscle marks are attached to the muscles inside the shell. Coat marks parallel to the abdominal edge of the shell; There are three muscle marks on the front part of the shell, and the largest one is oval, which is the muscle mark of the front closed shell; The upper edge of the back is a small slightly triangular foot muscle mark; After that, the lower line is the extensor sign. There are two muscle marks near the back edge of the shell, the big one is the closed shell muscle mark, which is oval, and the small one on the front upper edge is the foot contraction muscle mark.
cerebral cortex
There are two thin sheaths near the inner surfaces of the two shells, which surround the mussel body and have a sheathing cavity between them. The cilia on the inner surface of the sheath swing in a certain direction, causing water flow. Two sheathing films protrude slightly at the rear end to form a water outlet pipe and a water inlet pipe. The water inlet pipe is on the ventral side, with a long mouth and wrinkled edges, and there are many mastoid receptors on it; The outlet pipe is located at the rear side, with a small nozzle and smooth edge.
foot
Axe-shaped, flat left and right, muscular, located on the ventral side of visceral mass, protruding forward and downward. It is the motor organ of mussels.
muscle
Corresponding to the muscle marks on the inner surface of the shell, we can see the adductor and adductor muscles, which are thick columnar muscles connecting the left and right shells, and their contraction can close the shell. The front foot retractor, the rear foot retractor and the extensor muscle, one end of which is connected with the foot and the other end of which is attached to the inner surface of the shell, can contract and extend the foot.
digestive system
Before the mouth position is closed, it is a transverse seam under the muscle. There are a pair of triangular lips on both sides of the mouth, which are large and dense and have the functions of feeling and eating. Behind the mouth is a short and wide esophagus connected with an enlarged stomach. There are a pair of livers around the stomach, which can secrete amylase and sucrase, and a catheter enters the stomach. Behind the stomach is the intestine, which is coiled in the visceral mass and then shortlisted for the heart. The rectum passes through the ventricle, and the anus opens on the posterior obturator internus near the outlet pipe. There is a crystal rod between the gastrointestinal tract, which is a slender rod with a thick front end and a large morphological variation at the top end, which is slender, swollen, hooked and coiled. The crystal rod is located in the intestine, and its front end protrudes out of the stomach and is connected with the lower part of the gastric shield. Crystal stems can store food. In the absence of food, the crystal stem disappeared after 24 hours and was fed again. A few days later, the crystal stem recovered. Mytilus feed on organic particles, rotifers, flagellates, algae and small crustaceans.
respiratory apparatus
There are two membranes on both sides of the mussel in the mantle cavity, and the outer membrane is shorter than the inner membrane. Each branchial lobe consists of an inner branchial lobe and an outer branchial lobe, and its front and rear edges and ventral edges are combined into a "U" shape, and the rear edge is the suprabranchial cavity. Branchial lobules are composed of many vertically arranged gill filaments with cilia on the surface. The gill filaments are connected by a transverse junction between filaments, and there are small holes on it, which are called gill holes. There is an interlayer connection between the two branchial lobules, which divides the branchial cavity between the branchial lobules into many small tubes, called water tubes. There are blood vessels in the silk diaphragm and the valve diaphragm, and there are also blood vessels and several supporting chitin rods in the gill silk.
Because the cilia on the gills and the mantle swing, water flows into the mantle cavity from the water inlet pipe, enters the gill cavity through the gill hole, reaches the upper gill cavity along the water pipe, countercurrent and is discharged from the body through the water outlet pipe. When water passes through gills, gas exchange takes place. The mantle also has the function of assisting breathing. Every 24 hours, the water in the mussel can reach 40L, and the cilia on the gill surface can filter the tiny food particles in the water and send them to the mouth of the lip. Therefore, gills can still assist feeding. The gill cavity of the outer flap gill is also the place where fertilized eggs develop until hookworm larvae form.
circulatory system
It consists of heart, blood vessels and blood sinuses. The heart is located in the oval pericardial cavity on the back of the visceral mass, and consists of an oval ventricle and two thin-film triangular auricles. The ventricle extends an aorta forward and an aorta backward. The anterior aorta (aorta) that extends forward runs along the dorsal side of the intestine, and the posterior aorta extends along the ventral side of the rectum to the rear, and then branches into arterioles to the capsule and various parts of the body. Finally, it gathers in the blood sinus (external sinus, foot sinus, central sinus, etc.). ), enter the vein, enter the kidney through the renal vein, eliminate metabolites, enter the gill through the branchial vein, exchange oxygen and carbon, and return to the auricle through the branchial vein. Part of the blood enters the auricle from the vein of the tunica vaginalis, that is, the jacket circulation.
The blood of toothless mussel contains hemocyanin, which is blue when oxidized and colorless when reduced, and its binding ability with oxygen is not as good as hemoglobin. Generally, the oxygen content in the blood of mollusks 100ml is usually less than 3mg. The blood contains amoeba-like cells, which have phagocytosis. Therefore, in addition to transporting nutrients, blood also has the function of excretion. Amoeba-like cells aggregate, and their pseudopodes combine with each other, which makes blood coagulate (there is no fibrinogen in mussel blood).
Excretor
Mytilus has a pair of kidneys, which are specialized from the posterior renal duct, also known as Bojanus organs. There are pericardial glands, also known as Kjaerboel organs. The kidneys are located on the left and right sides of the ventral surface of pericardial cavity, and each kidney is composed of sponge glands and thin-walled tubular bodies with cilia, showing a "U" shape. The former is in the lower part, and the kidney mouth opens in the pericardial cavity; The latter is on the upper surface, and the renal foramen is open at the front end of the branchial cavity of the inner flap. The pericardial gland, located in the anterior wall of pericardial cavity, is a group of branched glands composed of flat epithelial cells and connective tissue. It is rich in blood and can collect metabolites, which are discharged into the heart cavity and excreted through the kidney. Phagocytosis between tissues also has excretion function.
nervous system
A toothless mussel has three pairs of ganglia. Below the adductor muscle, there are a pair of cranial nerve ganglia on both sides of the esophagus, which are very small, but they are actually formed by the merger of cranial nerve ganglia and pleural ganglion, which can be called pleural ganglion of the brain. A pair of long foot ganglia are buried in the front edge of the foot near the upper part, and they are combined together. A pair of visceral ganglion, healed and butterfly-shaped, are located under the epithelial cells in the ventral part of the posterior obturator internus, and the latter is larger. There are nerve cords between the three pairs of ganglia of brain, feet and organs, and the nerve cords of brain and organs are longer and more obvious.
The sensory organs of mussels are underdeveloped, and there is a balance sac near the foot ganglion, which is formed by the subsidence of foot epithelium. There are otoliths in it to balance the body. The epithelium above visceral ganglion becomes sensory epithelium, which is equivalent to osphradium of Gastropoda, and is a chemoreceptor. In addition, sensory cells are distributed around the mantle, lips and water pipes.
genital system
Mytilus is hermaphrodite, with gonads around the dorsal intestine of the foot, grape-like glands, ivory testis and yellowish ovaries. The reproductive ducts are connected, and the opening of the reproductive foramen is very small behind the renal foramen.
Reproduction and individual development
The breeding season of mussels is generally in summer, and sperm eggs are fertilized in the gill cavity of the outer gill. Due to the attachment of the mother, the fertilized egg will not be washed away by the current, but will remain in the gill cavity for development. Therefore, the gill cavity of everted gill is also called pouch. After completely unequal cleavage (spiral type), it develops into a blastocyst, and the gastrula is wrapped and invaginated to form a larva, which overwinters in the gill cavity. By observing the early embryonic cells of Anodonta dorsalis, it is determined that its chromosome is 2n=38 or 2n=37 (chromosome 19 is a single chromosome), and the difference between them is unknown, which may be related to the sex chromosome (Ma Qingfu et al. 1987). In the next spring, the larvae hatch and develop into hookworm larvae unique to freshwater mussels (equivalent to the face-plate larvae of other cladocera). Larvae have a double shell. There are well-developed adductor muscles and powerful hooks and teeth at the ventral edge of the shell. There is a thick filament in the center of the abdomen called foot silk. There are bristles on the side of the shell, which has sensory effect. Larvae has a mouth but no anus. Larvae can swim by opening and closing their double shells. Rhodiola chinensis, etc. In fresh water, insert a long oviposition tube into the water inlet pipe of Meretrix meretrix to lay eggs in the outer cavity of Meretrix meretrix. In this way, the hookworm larvae of mussels have the opportunity to contact peridermic fish and can parasitize on the gills and fins of fish. Stimulated by it, the skin of the fish proliferates abnormally, and the larvae are wrapped in their towels to form sacs. Larvae absorb fish nutrition through the mantle epithelium. After 2 15 weeks, it turned into a young mussel, broke its sac, left the fish and sank into the water to live. After five years of sexual maturity. Continue to grow in the future.
1988 One day, a farmer in Henan accidentally picked up a giant mussel weighing 13.8 kg from a river ditch. The curious owner took it home and was reluctant to eat it, so he dug a small pond in the yard and raised it. On the third day, the big clam escaped, and the owner had a hard time finding it from under the demolished courtyard wall. In order to prevent escape, the owner tied a rope to its shell. But a day later, when the giant clam had just escaped from the rope, it was discovered by its owner. This time, he was very angry with his master. He immediately prepared to kill it and cook it delicious at the party. It happened to be known by an aquatic science and technology personnel. He told his master that mussels, although surprisingly large, are only 65,438+02 years old, which is full of vigor and vitality. Therefore, in order to feast their eyes on it in the future, the owner built a new "villa" for it and cared more about its growth.