Molluscs or soft-bodied are a type of invertebrate animals. Their body consists of soft tissues, often there are protective horny formations like a shell. About ten classes of the Molluscan type are known.
Instructions
Step 1
The body of the mollusk is not divided into segments, it has three sections: head, leg and trunk. Some classes do not have one of the departments. For example, the head of Bivalves is reduced. With the help of the legs, the mollusks move, the body serves as a repository of internal organs. There is a specialized fold on the body, which forms a cavity associated with the external environment. The ducts of the reproductive, digestive and excretory systems exit into this cavity.
Step 2
The nervous system of molluscs is represented by the periopharyngeal nerve ring and four trunks. Two of them innervate the leg, the other two - the internal organs. The more developed representatives of the type have nerve nodes, the most developed of them located at the head end of the body. The circulatory system is predominantly open, that is, blood is poured from the vessels directly into the body cavity. After which it collects back into the vessels and goes to the respiratory organs. In the blood of molluscs there is a substance that gives it a bluish color. Only the Cephalopods have a closed circulatory system.
Step 3
The digestive system is also open, the anus extends into the cavity of the mantle. In the throat of most soft-bodied there is a special formation for grinding food. This formation is covered with tough chitin. The excretory system is the kidneys, the number of which may vary in different classes. The respiratory system of aquatic molluscs is represented by gills, while land mollusks have a lung. This lung develops from the mantle cavity. Molluscs can be both dioecious and hermaphrodite.
Step 4
Molluscs are both carnivorous and herbivorous, many of them parasitize on other creatures. They can feed on algae, protists, sponges, polyps, wood. There are even molluscs capable of photosynthesis by analogy with plants. They feed on algae, and the chloroplasts of the algae accumulate in the tissues of the mollusk.
Step 5
The most abundant class of molluscs is the Gastropoda class, which can inhabit almost all environments. The most famous gastropods are snails and slugs. Another class of molluscs is the Cephalopods, predatory inhabitants of the deep sea. The leg of the cephalopods has turned into tentacles with suckers, and the head is especially large. Very rare ones have a shell. Class Bivalve - sedentary molluscs with a closing shell.