What is the most primitive animal on Earth?

Sponges. Subkingdom: Protozoan subkingdom.

Phylum: Phylum Sponges.

There are about 5,000 species, divided into 790 genera and 80 families.

Distribution: Worldwide, from freshwater to marine, from intertidal to deep-sea.

Fossil record: originated in the Cambrian period, hundreds of millions of years ago; Of these, 390 genera have been confirmed to have originated from the Cretaceous period (100 million years ago).

Body size: from tiny to 2 meters long; The largest of these species are found in Antarctica and the Caribbean Sea.

Characteristics: Different forms; solitary or group; This porous filter-feeding organism is mostly "sessile" and attaches directly to the substrate; They have no organs, no clear tissues, but a very complex variety of cells; Their bones either do not have calcium- or silicon-containing bone needles, or they do not have organic sponge hard protein fibers; They are usually hermaphroditic and can reproduce both sexually and asexually.

Glass sponge or siliceous sponge.

Hexapochona sponge (hexaphosphorous sponge).

There are about 600 species, marine life, which generally inhabit below the tide line, but are more common in the deep sea. Its skeleton is a complex siliceous bone needle, and its basic form is hexagram. Genera and species include:

Foam sponge, Venus flower basket (Euplectella aspergillum), Holascus, circumference sponge.

Calcareous sponges Calcareous sponges.

There are about 400 species. Marine. The skeleton of calcareous bone needles is like a needle or three to four placements.

Genera include: acyssa, clathrina, leucilla, white-branched sponge, bottle sponge.

Common sponge Sponge Vulgar sponge.

There are about 4,000 species. Marine and freshwater. The skeleton either has no siliceous bone needles, or no organic sponge hard protein fibers, or neither.

When the bone needle is present, it is not hexagram. Genera and species include: Sponge, Cribochalina Vasulum, Cribochalina Vasulum, Hipposongia communis, Neofibularia nolitangere, Spongia officinalis, and needle.

Coral sponge Rigid sponge.

There are about 15 species. Marine, on shallow or deep burrows in the tropics or on corals underneath. The skeleton is calcareous and contains siliceous bone needles and organic fibers; A thin layer of sponge is formed that covers a calcareous base.

Genera include: ceratoporella, stromatospongia.

Sponge animals have germ layer reversal in reproductive development.

Marine life, formed in the sea.

The earliest fossils found are 3.5 billion years ago archaea, which are generally believed to have originated from single-celled prokaryotes, anaerobic, and originated in the ocean.

Protozoan. Protozoa is the lowest class of animals, its individual is composed of a cell, common protozoa are euglena, paramecium, etc. Protozoa are tiny, the smallest is only 2 3 microns, generally more than 10 200 microns, except for some species of marine foraminifera that can reach 10 cm, the largest is about 2 mm.

Protozoa live in a wide range of areas, living in seawater and freshwater, benthic or planktonic, but many live in soil or parasitize other animals. Protozoa generally reproduce in a way that alternates between sexual and asexual generations.

The earliest animal on earth was actually a jellyfish.

The earliest animal on earth was actually a jellyfish.

The necessary step in the evolution of life is the evolution of these organisms, which not only have cells, but also play a role in controlling specialization. These Precambrian fossils of marine life were buried in the rocky layers of the early oceans and were found off the coast of Ediacala in Australia.

The earliest animals on earth.

The oldest traces of animal life date back to 1 billion years ago, and the earliest animal fossils appeared 600 million years ago, during the Sinian period. The most primitive lower animals live on the seabed and in the vicinity, with soft bodies that can only be seen in the microscopic realm. Almost none of these animals have formed fossils, leaving only some traces such as caves, traces, etc.

Floating life.

The Silurian oceans were home to another very small species of zooplankton, which was very light and floated in the water, and the penstone appeared in the Cambrian period, flourished for 200 million years, and then the entire population became extinct. A single stone is generally no more than a few millimeters, but a group of penstones can be up to 20 centimeters long, or even longer. They come in various shapes; Some resemble leaves or branches, some resemble tuning forks, wheels, and some even resemble spider webs.

Brachiopods. Brachiopods are another type of animal that is in the middle of the "original mouth" and "back mouth". Their bodies are unsegmented but cavities, fixed to sediment or other objects with fleshy feet, and brachiopods are distinguished from valve-gill animals by having two shells with different beginnings; There are two spiral-shaped oral wrists on either side of the mouth, and there are ciliary grooves and ciliated tentacles on the oral wrists. The mouth wrist was first mistaken for an axe foot similar to a river mussel, hence the name "brachiopod".

The primitive species of brachiopods appeared before the Cambrian period, flourished during the Paleozoic Era, and then declined. Their dominant position in the oceans has now been replaced by mollusks.

The earliest animals on Earth appeared around the time of the Aurora period.

We don't know what happened in the long 1.6 billion years between 3.4 and 1.8 billion years ago (and probably no more than a billion years since the first animal on Earth), but one thing is for sure, primitive eukaryotic cells are constantly evolving. Since 1.8 billion years ago, the earth entered the Sinian period, and after about 1.2 billion to 600 million years ago, eukaryotic organisms with nuclei and organelle differentiation appeared, and since then the earth has entered a stage of great development of life. The marine life of this period was mainly cyanobacteria, red algae and green algae, and protozoa probably appeared during this period, and by 600 million years ago, there were zooplankton, cup sponges and coelenterates.

The world is so big that our earth has undergone hundreds of millions of years of changes, and there have been many creatures, in the earliest days of the dinosaurs.

Dinosaurs appeared, but at that time we only remembered the appearance of dinosaurs, but did not notice the appearance of other creatures.