Invertebrate animals

Invertebrate animals are numerous representatives of fauna that do not have a spine. This category includes protozoa (unicellular), lower worms, sponges, arthropods, mollusks, echinoderms and others. There are sixteen types in this group.

The division of the animal world into vertebrates and invertebrates was carried out by Lamarck in 1801. Among vertebrates, about forty-five thousand species are known. Known invertebrate animals are represented in an amount of 1 million 260 thousand species. In this case the protozoa are about twenty-five thousand, sponges about five, lower worms about twenty, mollusks more than a hundred, arthropods - about seventy-nine thousand species.

The largest number of species are insects. There are about a million of them. At the same time, water insects belong to many detachments. It should be noted that some of them are present in the water only during the larval period. While others are in it for life. The intestinal animals have about nine thousand species. It should be noted that there are much more existing types in nature than is known. In addition, several thousand new ones are annually determined.

Invertebrate animals inhabit the soil, oceans, seas, rivers, lakes, ponds. Many of the representatives are parasites. In this case they parasitize both on animals and on plants.

The role of invertebrates in nature is great enough. Solid remains of representatives who lived in the early geological epochs, became elements of rocks, and in some cases - their main mass. For example, the skeletons of invertebrate animals, long extinct, almost completely constitute limestones.

The meaning of representatives of this group is also diverse for man. So, many invertebrate animals, as well as their products of vital functions, are used for cooking food for humans (honey bees, for example). Many representatives are used to feed commercial fish, animals, birds. Pearls, shells of mollusks, beeswax and many other products of vital activity of representatives of the group of invertebrates are of great economic and technical importance. They are often used in pest control. Invertebrates are predators and parasites that destroy them. This method refers to biological methods of pest control. Geologists in the determination of the age of sedimentary rocks investigate the remains of fossil invertebrates.

However, there are a lot of harmful representatives of this group in nature. Many invertebrates are carriers of parasitic and infectious pathologies, pests of grain and products from it. They can be poisonous, and also cause damage to crops, forests, etc.

A special place in the group is occupied by coelenterates. In describing traditionally, there is a presence of radial symmetry, as well as two germ layers (ectoderm and endoderm). Usually it is believed that the body of animals is formed from two epithelial layers: the outer covers (epidermis) and lining in the intestinal cavity (gastrodermis). Between the layers is a connective tissue jelly-like interlayer (mesogloe). In its composition there are collagen fibers and amoeboid cells in a small amount.

Representatives of coelenterates lack specialized respiratory organs and secretions. This, as a rule, is associated with a two-layer structure of the structure, which involves contacting the majority of epithelial cells with the external environment.

For coelenterates, the underdeveloped nervous system is characteristic. Most reproduce sexually and is characterized by the presence of crawling or planktonic larvae.