In biology, all living organisms that existed and exist on our Earth are divided into four huge groups called kingdoms. These are bacteria, plants, fungi and animals. Each kingdom includes a great many genera and species, consisting of a large number of units. Striking the imagination and the huge diversity of the animal world. In turn, animals are divided into unicellular and multicellular, invertebrate and vertebral organisms. And the science involved in their study is called zoology (section of biology).
Animal Variety: Classification
Invertebrates usually include worms, mollusks, 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 (a person belongs to the latter class, because he feeds his young with breast 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 different directions. They live in seas, rivers, lakes, swamps, in the land. Bright, well-known representative - the earthworm. He lives in the soil, helping to loosen and enrich it. This is very important for all kinds of agricultural work. Many of the worm class are useful. For example, leeches. They are used in medicine. And sea worms serve as a 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 (parasitic on them). Due to insufficient compliance with the rules of personal hygiene, such parasites can enter 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 prevent the presence of flies. By the way, worms, settling inside other organisms, secrete 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 a constant intoxication of the body, and serious intervention by doctors is already necessary, removing all this living creature from the human body by special means.
Mollusks
The variety of mollusk animals is also great. This group has more than 130 thousand species. And they live almost everywhere, even on trees. But most of them live in the oceans at various depths. Some of them are hundreds of years old. Shellfish feed on plants, small animals, and organic waste. Almost all of them have shell protection (except, for example, squid, which is also a mollusk, but it also has the rudiments of a shell). Since ancient times, people have been using mollusks as food. Some representatives of this group are even delicacies.
Echinoderms
These are starfish (1,500 species), which got their name due to the presence of rays on the body (many have five, but some even count up to 50). Stars living in the sea vary in size and appearance. A characteristic feature of a starfish is its ability to regenerate (like that of lizards). If an animal has been torn off a limb, then in its place a new one grows in speed. And under favorable conditions, a new individual develops from the torn beam. Most starfish are predators.
Sea urchins (800 species) are also echinoderms. The body of the hedgehogs is covered with needles of various sizes. And the length of the shoots can reach up to 30 centimeters. Hedgehogs move with needles. And among them there are very poisonous, dangerous to other animals.
Crustaceans
The body of these animals consists of armored segments: head, chest and abdomen. The limbs located on the abdomen and chest allow the cancers to move on the surface. Their eyes consist of many 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, of which there are 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 have no wings. Also, the body structure is different: insects have a head, chest and abdomen, and spiders have a cephalothorax and abdomen.
Vertebrate animals
The variety 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 from time immemorial (sharks, brushfish). These are amphibians, and reptiles, and birds, and mammals that inhabit the surrounding world.
The diversity of animals is so great that even an experienced zoologist will not give an exact answer to the question of how many animal species exist in nature. Because there is no final answer: new ones constantly open, some existing species disappear. The nature cycle is being carried out, including an endless variety of animals (see photo above).