In our article, we will consider the structural features of mollusks, which are called "shipworms." No, we were not mistaken - such animals really exist.
Shipworm: class and type of animals
The thing is that the shipworm, which is also called the forewort, or woodworm, underwent significant changes during evolution. Especially they relate to the external structure of the animal. Therefore, at first glance it is quite difficult to figure out which class the shipworm belongs to. In fact, it is a representative of the subdomain Multicellular and type Mollusks. The class that represents the shipworm is called the "Bivalve".
External structure
Theredo has a cylindrical body that reaches a length of about a meter. Since the shipworm belongs to the class of bivalve mollusks, it has inherent structural features. Where is his sink? It is located at the front end of the body and consists of two small cusps about 1 cm in size. With their help, the mollusk drills wood. Each leaf is formed by three parts with serrated edges.
The rest of the mollusk shipworm has structural features typical of this systematic unit. His body is flattened from the sides and consists of two departments: the trunk and legs. Since bivalve mollusks do not have a head, they also have no organs located on it. These are tentacles, pharynx, tongue with a grater, jaw and salivary glands. The mantle covers the back of their body. There are also glands that secrete calcareous matter.
Almost the entire body of a shipworm is in wood. On the surface, it leaves only the rear end with a pair of siphons. Through them, the animal is interconnected with the environment. The protection mechanism is also interesting. Along with siphons, at the rear end of the body is a plate of solid chitin carbohydrate. In case of danger, the animal draws siphons into the tree passage. And the hole is closed with a chitin plate.
Habitat
All bivalves live in the water. They can be found in all seas, excluding only the coldest. This is due to the fact that they feed on by filtration. The shipworm passes water through siphons with organic residues that are in it. Another source of power is wood. With the help of a reduced shell, they make moves in it. Therefore, they live in the woods of marinas and ships, driftwood that have fallen to the bottom, and rhizomes of marine plants.
Internal structure
Like all mollusks, shipworms have a secondary body cavity. However, the gaps between the organs are filled with loose connective tissue. The circulatory system of these animals is open. It consists of the heart and blood vessels. Blood from arteries enters the body cavity. Here it mixes with liquid and washes all organs. At this stage, gas exchange is carried out. Blood enters the heart through the veins. The shipworm is a cold-blooded animal. Therefore, he cannot live in very cold water.
The respiratory organs of the woodworm are the gills, with the help of which it absorbs oxygen from the water. The excretory system is represented by the kidneys. They secrete metabolic products into the near-mantle cavity. The shipworm has a scattered-nodal nervous system.
Features of life
Shipworms are in constant action. In a minute they make about ten drilling movements. At the same time, they open the wings, which with their notches destroy the wood. The dimensions of the moves of the shipworm increase with the growth of the animal itself. They can reach 2 meters in length with a diameter of 5 cm. Another name is associated with this lifestyle - woodworms. Surprising is the fact that the moves of these mollusks never intersect. Scientists suggest that they hear the approaching sounds of drilling "neighbor" and change their direction. Here is such respect animals show to each other!
To digest the complex carbohydrate cellulose that makes up wood, certain enzymes are needed. Of course, they are not capable of independently developing them. A feature of the structure of their digestive system is the presence of a long blind outgrowth of the stomach, in which sawdust is constantly accumulating. Symbiotic bacteria live here. They break down cellulose to glucose monosaccharide. Another function of the symbionts is the fixation of nitrogen in the water.
Reproduction and development
Shipworms are hermaphrodites. This means that one individual forms both male and female sex cells. Fertilized eggs are first located in the gill cavity, in which they develop up to 3 weeks. Their larvae develop them. They go into the water and swim here for another 2 weeks. The leg of the mollusk begins to secrete a special protein substance in the form of a thread - a bisus. With its help, the larva attaches to wood. During this period, the queue has the typical appearance of a bivalve mollusk. Most of his body is hidden by shells, from which the leg protrudes markedly. As it develops, the animal becomes like a worm.
Significance in nature and human life
Shipworms have rightfully earned unkind fame. They really do a lot of harm by destroying wood on their own. These animals were especially dangerous in ancient times, when people did not yet know about methods of dealing with them. Shipworms are able to completely destroy the bottom or sides of the ship, turn the supports of bridges and marinas into dust, cause the death of marine plants. Now the wood, which may become a “victim” of shipworms, is coated with special toxic substances that make it “inedible” for these mollusks.
So, shipworms, despite their name, are representatives of the class "Bivalves". They live in almost all seas, settling on woody objects. These animals have an elongated soft body and two reduced shell folds. With their help, they make moves in the wood, thereby destroying it and causing great harm.