In our article we will consider the structural features of mollusks, which are called "shipworms". No, we were not mistaken - such animals do exist.
Shipworm: class and type of animals
The fact is that the shipworm, which is also called teredo, or woodworm, has undergone significant changes in the course of evolution. Especially they concern 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, this is a representative of the sub-kingdom Multicellular and the type of Mollusks. The class that the shipworm represents is called Bivalves.
Exterior structure
Teredo has a cylindrical body that reaches a length of about a meter. Since the shipworm belongs to the class of bivalve molluscs, it has structural features inherent in them. Where is his shell? It is located at the front end of the body and consists of two small valves about 1 cm in size. With their help, the mollusk drills wood. Each leaf is formed by three parts with serrated edges.
Botherwise, the shipworm mollusk has structural features typical of this systematic unit. Its body is flattened from the sides and consists of two sections: the torso and legs. Since bivalves do not have a head, they also lack organs located on it. These are tentacles, pharynx, tongue with a grater, jaws and salivary glands. The mantle covers the back of their body. The glands that secrete calcareous substances are also located here.
Practically the entire body of the shipworm is in the wood. On the surface, it leaves only the rear end with a pair of siphons. Through them, the relationship of the animal with the environment is carried out. The teredo defense mechanism is also interesting. Along with siphons, at the posterior end of the body is a plate of solid carbohydrate chitin. In case of danger, the animal draws the siphons into the tree passage. And the hole is closed with a chitinous plate.
Habitat
All bivalves live in water. They can be found in all seas, except for the coldest ones. This is due to the fact that they feed by filtration. The shipworm passes water with organic residues that are in it through siphons. Another source of nutrition for teredo is wood. With the help of a reduced shell, they make moves in it. Therefore, teredos live in the wood of piers and ships, snags that have fallen to the bottom, and the rhizomes of marine plants.
Internal structure
Like all mollusks, shipworms have a secondary body cavity. Howeverthe 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 the arteries enters the body cavity. Here it mixes with the liquid and washes all the organs. At this stage, gas exchange takes place. In the heart, blood flows through the veins. The shipworm is a cold-blooded animal. Therefore, he cannot live in very cold water.
The woodworm's respiratory organs are gills, with which it absorbs oxygen from the water. The excretory system is represented by the kidneys. They secrete metabolic products into the perimantle cavity. The shipworm has a scattered-nodular nervous system.
Features of life activity
Shipworms are in constant action. In a minute they make about ten drilling movements. At the same time, they push the doors apart, which destroy the wood with their notches. The dimensions of the shipworm's moves increase as the animal itself grows. They can reach 2 meters in length with a diameter of 5 cm. Another name is associated with this way of life - woodworms. Surprising is the fact that the passages of these mollusks never intersect. Scientists suggest that they hear the approaching sounds of drilling "neighbor" and change their direction. That's the kind of respect animals show for each other!
Specific enzymes are needed to digest the complex carbohydrate cellulose that makes up wood. Teredos are not capable of producing them on their own. featurethe structure of their digestive system is the presence of a long blind outgrowth of the stomach, in which sawdust constantly accumulates. Symbiotic bacteria live here. They break down cellulose into the monosaccharide glucose. Another function of the symbionts is to fix nitrogen in the water.
Reproduction and development
Ship worms are hermaphrodites. This means that one individual forms both male and female germ cells. Fertilized eggs are first located in the gill cavity, in which they develop up to 3 weeks. Their larvae develop. They go out 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 - bisus. With its help, the larva is attached to the wood. During this period, the teredo has the typical appearance of a bivalve. Most of its body is hidden by shells, from which a leg protrudes noticeably. As the animal develops, it becomes like a worm.
Meaning in nature and human life
Shipworms have rightfully earned a bad name. They really do a lot of harm, destroying wood with their moves. These animals were especially dangerous in ancient times, when people did not yet know about the methods of dealing with them. Shipworms are able to completely destroy the bottom or sides of the ship, turn the supports of bridges and piers into dust, and cause the death of marine plants. Now wood, which can become a "victim" of shipworms are 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 valves. With their help, they make moves in the wood, thereby destroying it and causing great harm.
