When did invertebrates appear

I know that due to the change in the composition of the air, the proportion of oxygen has gradually increased, most of the invertebrate lower organisms have suffocated to death, most of the living things have become extinct, and only a few vertebrate animals have adapted to oxygen by their own strong adaptability, so that most of the present organisms should survive on oxygen.

This is what I found.

Microbial changes are closely related to the extinction of invertebrate groups, and there were at least two biological crises during the largest global extinction in the Phanerozoic. Professor Xie Shucheng and Academician Yin Hongfu of China University of Geosciences (Wuhan) collaborated with British scholars to reveal this important discovery through the study of molecular fossils in the Permian-Triassic boundary section of Changxing Coal Mountain, Zhejiang, China, and published the research results in the journal Nature.

The D section of Changxing Coal Mountain in Zhejiang Province, China has become a stratigraphic profile and point (GSSP) of the global Permian-Triassic boundary, commonly known as the "golden nail", which is a key profile for the study of geological science problems related to the Phanerozoic extinction document. For a long time, knowledge of the extinction of the boundary cluster has been largely derived from the large fossil and microfossil records preserved in the strata, with a focus on marine invertebrates, but this has only involved a relatively small part of the ecosystem. The work of the primary producers (especially algae, cyanobacteria, etc.) and decomposers (fungi) of the ecosystem was relatively weak, and it was difficult to respond to the crisis of the entire ecosystem at that time.

Xie Shucheng et al. used organic geochemical methods such as gas chromatography and gas chromatography-mass spectrometry to study the molecular fossils near the boundary and detected a series of organic molecules with clear biological significance. One of these organic compounds is 2-methylquiane, which is the marker compound of cyanobacteria at the bottom of the marine food chain, and the changes in these compounds can reveal the changes in cyanobacteria in the ocean at that time. The results of the study found that there were at least two drastic changes in cyanobacteria in the boundary.

In order to further understand the relationship between cyanobacterial changes and the extinction of invertebrate groups, Xie Shucheng et al. calculated the extinction rate of invertebrates in the corresponding layer based on the distribution of fossil species in each stratum near the boundary. The results show that there is a good coupling relationship between the peak of animal extinction and the 2-methylquil index, which reflects the changes in cyanobacteria, in strata, which reflects the common response of microorganisms and animals to catastrophic events, which led to the extinction of animal clusters and subsequent ecosystem changes.

According to Xie, the work provides a window for further study of the anomalous ecosystems associated with the extinction of animal clusters, especially the ecology of communities at the bottom of the food chain.

I'm not sure of its authoritative nature, it's in the newspapers.

Roughly there are these: echinoderms (starfish, sea urchins, sea cucumbers), molluscs (squid, octopus, nautilus), coelenterates (anemones, hydroids, jellyfish), arthropods (shrimp, crabs, trilobites, horseshoe crabs, spiders, scorpions), sponges (sponges), nematodes (hookworms, nematodes), annelids (earthworms, leeches), star insects (star insects).

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.

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.