What animals are invertebrates?

All invertebral animals account for more than 90% of all extant animals. Found all over the world, in size, from small protozoa to giant squid. In general, the body is soft and does not have a hard endoskeleton that can attach muscles, but there are often hard exoskeletons (such as most molluscs, crustaceans and insects) to attach to the muscles and protect the body.

If classified by morphology, invertebrates are first divided into two types: single-celled animals (protozoa) and multicellular animals (i.e., metazoans) according to the number of cells they compose. The former belong to controversial animals, such as euglena, which are classified as plants because of the chloroplasts in their bodies.

Multicellular animals are further divided into parazoa and eumetazoa. The former include sponges, flat discs, and mesozoans. These three animals are not connected to the true metazoans. The degree of tissue differentiation is low.

Next, eumetazoans are divided into radially symmetrical and bilaterally symmetrical according to their body symmetry. The former includes the phylum Cnidarians and the phylum Ctenophorae.

Then, the symmetrical animals on both sides are divided into three categories according to the presence or absence of their body cavities, if they are true or false, namely acoelomata, pseudocoelomata and eucoelomata. However, the phylum Nephyta is between prosthetic coelage animals and eubody coelage animals, and the taxonomic position is questionable. Representatives of coelageless animals are flattened animals.

The body cavity of prosthetic cavity animals is not surrounded by mesoderm, but is the product of incomplete degeneration of the gastrum, and the representative animals are nematode animals and rotiformes. The body cavity of eucocoides is encased in a mesoderm.

True coelozoa are then divided into protostomia, posterior and tentacular animals (tentaculata) according to the development of blastopores. Representatives of posterior mouth fauna are echinoderms (and non-"invertebrate" chordates). The transition types include broom worms, brachiopods, and bryozoans.

Other eucococytes are protostomates, including arthropods, tardigrades, clawed animals, molluscs, star insects, mites and annelids.

There are big problems with this classification, such as the "homelessness" of neuromorphs, while flattened animals and nematode animals are protostotic animals, but they are not "qualified" to be classified because their body cavity is not a "true body cavity". Tentacle animals have many features of posterior animals, such as radiated cleavage, and the body cavity is enclosed by the mesoderm formed by endoderm invagination. But evidence from molecular biology suggests that they are protostomates.

Nowadays, the animal kingdom is generally divided into ten phyla.

Including Protozoa, Pores, Coelenterates, Platyzoa, Linear Animals, Annelids, Molluscs, Arthropods, Echinoderms, Chordates, Chordates, Cercocephalic Cords, Hemichordates, and Vertebrates. With the exception of the subphylum Vertebrates, all other animals are invertebrates.

Invertebrates (invertebrata are animals without a vertebral column on the dorsal side, and their species number accounts for 95% of the total number of animal species. They are the original form of animals. A general term for all sectors of the animal kingdom except for the kingdom Protozoa and the subphylum vertebrates.

1. Invertebrates are animals that do not have a vertebral column on the dorsal side, and they are the primitive form of animals. The number of species accounts for 95% of the total number of animal species. It is distributed all over the world, and there are about 100 million species in existence.

Including protozoa, echinoderms, molluscs, flattened animals, annelids, coelenterates, arthropods, nematozoa, etc.

2. A sub-discipline of zoology. In the classification of schizoa, animals are divided into two categories: vertebrates and invertebrates according to whether they have vertebrae in their bodies. The science that studies the classification, morphology, physiological characteristics, geographical distribution, reproduction, evolution, etc. of invertebrates is called invertebrate zoology.

Invertebrate zoology includes: protozoology, helminthology, entomology, molluscs, crustaceans, etc.

3. Invertebrates include these: ants, snails, silkworms, mussels, clams, mussels, butterflies, jellyfish, octopus, loaches, eight eyelashes, lilies, sea cucumbers, gall galls, starfish, octopus, cuttlefish, squid, shrimp, crabs, spiders, mosquitoes, flies, centipedes.