In biology, all living organisms that have existed and still exist on our Earth are divided into four huge groups called kingdoms. These are bacteria, plants, fungi and animals. Each kingdom includes a great variety of genera and species, consisting of a large number of units. Amazes the imagination and the huge diversity of the animal world. In turn, animals are divided into unicellular and multicellular, invertebrate and vertebrate organisms. And the science that studies them is called zoology (a branch of biology).
Animal Diversity: Classification
Invertebrates usually include worms, molluscs, echinoderms, crustaceans, arachnids and insects. These animals (yes, worms are also animals!) do not have a pronounced spine inside or outside. Sometimes there is a chitinous shell that performs this role. Vertebrates include fish, amphibians, reptiles, birds, mammals (man belongs to the last class, because he feeds his youngbreast milk).
Invertebrates: worms
The diversity of the animal world can be well represented by studying these creatures. This group includes more than 46 thousand species of organisms. Worms move with the help of elastic muscles, bending the body in various directions. They live in the seas, rivers, lakes, swamps, in the ground. A bright, well-known representative is an earthworm. It lives in the soil, helping to loosen and enrich it. This is very important for all kinds of agricultural work. Many of the class of worms are useful. For example, leeches. They are used in medicine. And sea worms serve as constant food for commercial fish caught by fishermen. Without them, some species of fish simply would not have food. However, there are many parasitic worms that exist at the expense of other organisms (parasite on them). Due to insufficient observance of the rules of personal hygiene, such parasites can get inside the human body and live there for years. So now you understand how important it is to follow simple hygiene rules: wash your hands before eating, do not use dirty dishes, and do not allow the presence of flies. By the way, worms, settling inside other organisms, emit harmful products of their vital activity, gradually poisoning their host. A person becomes nervous, everything in the world irritates him, he quickly gets tired and weakens, there is constant intoxication of the body, and serious intervention of doctors is already necessary, removing all this living creatures from the human body with special means.
Shellfish
The variety of shellfish animals is also great. This group includes more than 130 thousand species. And they live almost everywhere, even on trees. But most of them live in the world's oceans at various depths. Some of them are hundreds of years old. Mollusks feed on plants, small animals, and organic waste. Almost all of them have protection in the form of a shell (except, for example, squid, which is also a mollusk, but it also has the rudiments of a shell). People have been using shellfish as food for a long time. Some members of this group are even delicacies.
Echinoderms
These are starfish (1500 species), which got their name from the presence of rays on the body (many have five, but some even have up to 50 pieces). The stars living in the sea differ in size and appearance. A characteristic feature of the starfish is the ability to regenerate (like lizards). If a limb is torn off from an animal, then a new one grows at a speed in its place. And from the torn off beam, under favorable conditions, a new individual develops. Most starfish are predators.
Sea urchins (800 species) are also echinoderms. The body of hedgehogs is covered with needles of various sizes. And the length of the processes can reach up to 30 centimeters. Hedgehogs move with the help of needles. And among them there are very poisonous, dangerous for other animals.
Crustaceans
The body of these animals consists of armored segments: head, chest and abdomen. Limbs, located on the abdomen and chest, allow crayfish to move along the surface. Their eyes are made up ofmany small eyes, and on the head there are several pairs of jaws.
Arachnids and insects
The variety of animals living on Earth is well represented by these groups, which number more than 27 thousand species. These two groups are related. Only insects have six legs, and spiders have eight. All insects also have wings, even in their infancy. Spiders do not have wings. Also, the structure of the body varies: insects have a head, chest and abdomen, and spiders have a cephalothorax and abdomen.
Vertebrates
The diversity of animals living on our planet is easy to imagine by studying the order of vertebrates. These are fish covered with scales. Their great variety of species, among which are very ancient, inhabiting the waters of the ocean since time immemorial (sharks, lobe-finned fish). These are amphibians, and reptiles, and birds, and mammals that inhabit the world around us.
The variety of animals is so great that even an experienced zoologist will not give an exact answer to the question of how many species of animals exist in nature. Because there is no definitive answer: new ones are constantly being discovered, some existing species are disappearing. The cycle of nature is carried out, including an endless variety of animals (see photo above).
