At present, animal taxonomists classify animals according to their various characteristics (morphology, cell, heredity, physiology, biochemistry, ecology and earth distribution), that is, natural classification, and divide animals into various grades in turn. There are mainly seven grades: boundary, phylum, class, order, family, genus and species. One of them is the basic unit used in classification. Each animal can be given an appropriate name and occupy an appropriate position in this hierarchical sequence. Such as cotton aphid, belonging to the animal kingdom, arthropoda, Insecta, Homoptera, cotton aphid; ; The giant panda belongs to the animal kingdom, Amphibia, Mammalia, Carnivora and Giant Panda, and its scientific name is Ailuropodamelanoleuca. In the above classification levels, in order to express the taxonomic status of species more accurately, scientists further subdivided the original order elements and added other order elements between the above classification order elements to meet the needs of scientific work. Therefore, in practical work, the commonly used classification appendages are as follows: phylum superfamily, superclass, superclass, subclass, subfamily, subfamily, subgenus. According to the changes of appearance, internal anatomy and physiological characteristics in the process of animal purchase, zoologists of subspecies of Chinese species have developed a key table, which can reflect the genetic relationship between species. Such as spiders, insects, earthworms, carp, cobras, frogs, red-crowned cranes and South China tigers. Please refer to the following key tables to understand their similarities and differences. First, like the real chordates (chordates), it is composed of head, chest and abdomen, which are fertilized in vivo to produce sheep eggs; Fingers (toes) have claws, the body surface is covered with horny scales, double breathing, with airbags and sound pipes; There are many kinds of animals in nature, such as laying eggs, raising chickens by instinct, viviparous and breastfeeding. It is estimated that there are about 6.5438+0.5 million species. In order to know, study and use animals, we must classify them. Although different animals have different shapes, animals in the same group often have many similarities in shape, so zoologists will learn from childhood according to their similarities and differences. Divide into many groups. 1. "Species" or "species" is the smallest group. It is also the basic unit of animal classification. 2. Assemble similar "species" into "genera". 3. Assemble approximate "genera" into "families". 4. Assemble "home" into "order" or "order". 5.m)。 "Door" is the largest classification unit. At present, the animal kingdom is divided into more than 20 phyla, among which the main phyla are: 1. Protozoa, such as grasshoppers and amoebas; 2. Sponges, such as hair pots and bath sponges; 3. coelenterates, such as jellyfish and corals; 4. Platforms, such as planarian and Schistosoma japonicum; 5. Linear animals, such as roundworms and other parasitic nematodes parasitic in plants and animals; 6. annelids, such as earthworms, nereis and leeches; 7. Molluscs, such as snails and squid; 8. Arthropods, such as shrimp, crabs and insects; 9. Echinoderms, such as sea cucumbers and starfish; 10. Vertebrates, such as fish, frogs, turtles, snakes, birds and beasts. With the development of science and technology and the increase and accumulation of zoology knowledge, people have more and more in-depth means and methods to supplement the characteristics of animals. At present, we not only compare animals according to their morphology, but also use embryology, biochemistry, mathematics and other methods to study animal classification. It is not artificially arranged and combined according to the similarities and differences of animal surfaces, but reflects the development history of animals. Animals in the same group are relatively related animals, such as shrimp and crab, which belong not only to Crustacea, but also to Decapoda. They all have five pairs of gait for crawling, and the first pair of gait usually becomes pliers. Not only because of their similarity in morphology, but also because of their reactions. On the other hand, some morphological characteristics are not so similar, and the genetic relationship is far away. According to the genetic relationship, the relationships of various animals can be arranged into a "phylogenetic tree", where the animals below the "tree" are primitive and the animals above the "tree" are higher. It is very useful to study the classification of animals in theory and practice. The genetic relationship between animals is the evolutionary relationship of animals. The emergence and development of evolutionism.