Are vertebrates and cephalic chordates, caudal chordates homologous?

Different sources. Chordates, also known as "headless animals", are phylum chordates.

A subdoor. It is a group of headless fish-shaped chordates with lifelong characteristics such as a well-developed notochord, dorsal neural tube, and pharyngeal gill slits. There are few species, and the representative animal is Wenchang fish.

The notochord of the cephalochordate subphylum cephalochordata is not only preserved for life, but also extends to the front of the dorsal neural canal, so it is called cephalochordate. And because the animals of this subphylum lack real heads and brains, they are also called headless. Chordates are widely distributed in tropical and temperate shallow seas, especially in coastal areas between 48°N and 40°S.

They have strict substrate requirements and are usually confined to pure coarse and medium sand with low organic matter content. The body is buried in the sand, with only the front end exposed, which is used for respiration and filtering of diatoms in water bodies. Only 1 class, that is, cephalochorda, commonly known as Wenchang fish, its name is Wenchang Pavilion on Liuwudian Haiyu in Tong'an County, Xiamen.

This is the first place in China where Wenchang fish were discovered. Legend has it that when the ancient Wenchang Emperor rode a crocodile across the sea, many small maggots fell from the crocodile's mouth, and when these small maggots fell into the sea, they became many elephant fish.

This kind of animal allows future generations of fishermen to catch this fish for a living, so it is to commemorate Emperor Wenchang.

Therefore, it was named Wenchang fish. Wenchang fish is rich in nutrition, the meat is fresh and tender, so it has been caught in large quantities, and the population of Liuwudian in Xiamen, which was once rich in Wenchang fish in China, is endangered and is now a national second-class protected animal.

Xiamen Wenchang Fish Nature Reserve has been established. <>

The phylum Chordates is one of the highest phylums in the animal kingdom. There are more than 70,000 species. The morphological structure and lifestyle are different, and the differences are very significant.

However, it has the following common characteristics: (1) the embryonic stage or adult has the notochord as the longitudinal axis to support the body, some lower species of notochord survive for life, and many higher species only appear in the embryonic stage, and are replaced by segmented spine when they become adults; (2) It has a dorsal neural tube, and the central nervous system of chordates is tubular and located on the back of the notochord, so it is called the dorsal neural tube; (3) the pharynx has a gill slit; (4) The gill slits of the lower species of adults are directly or indirectly connected with the outside world, and when the water flows through, gas exchange is carried out here, which is an important respiratory organ; (5) Gill clefts of higher species appear only in the embryonic stage, disappear when they become adults, or transform into other structures.

Chordates are one of the highest taxa in the animal kingdom and a phylum with a wide variety of species. It includes from the lower ones such as the Wenchang fish and sea squirts in the modern ocean, to the higher ones such as fish, frogs, turtles, birds, cows, apes, humans, etc.

An important common denominator of chordates is the notochord, which all chordates have at least during the embryonic period. The notochord is a longitudinal rod-like structure in the back that functions as a support body axis, located between the digestive tract and the neural tube.

The notochord** is formed in the dorsal wall of the gastrula in the embryonic stage, thickened, differentiated, protruded, and finally separated from the gastrum.

Function of the notochord

The central axis support of the notochord also enables the animal body to complete the directional movement more effectively, which is more accurate and fast for active predation and evasion of predators. The formation of vertebrate skulls, the appearance of jaws, and the protection of the central nervous system by the spinal canal are all further refined developments on this basis.

The notochord also induces peripheral cell differentiation in terms of genesis and embryology, and promotes the generation and perfection of the spine developed from the mesoderm and the nerves developed from the ectoderm during the embryonic stage. This is one of the reasons why the vertebral cords still exist in the embryos of higher chordates.

I'll be honest with you, I don't know.