When describing the development of living organisms, the terms "protostomes" and "deuterostomes" can often be found. These are all existing multicellular organisms, except for the coelenterates, which differ at the embryonic level.
Development of chordates
Chordates are represented by three groups of organisms:
- tunicates, or larval-chordates (Tunicata, Urochordata), which have a sac-like body wrapped in a shell;
- cranial, or cephalochord (Acrania), living in the depths of the sea fish-like sedentary creatures;
- vertebrates - representatives of fish, amphibians, snakes, birds, animals and humans.
The history of the origin of chordates is shrouded in mystery and causes many assumptions. And in order to concretize them, you need to figure out who the deuterostomes and protostomes are. It is authentically known that more than 500 million years ago there were already cephalochords. The previous stages remain mysteries, so there arevarious hypotheses of the origin of living beings.
Essence of protostomes and deuterostomes
Metazoans represent the Animal Kingdom. Protostomes and deuterostomes are their direct ancestors. Their verbal designations Protostomia and Deuterostomia are formed from the peculiarities of the formation of the mouth in embryos. In the former, it is formed from the opening of the primary intestine (blastopore), which is formed in the embryo. In the second, an excretory opening (anus) develops in the blastopore, and the oral opening is cut in a new place.
Classification of bilaterally symmetrical organisms
Deuterostomes and protostomes have their own classifications. Primary mouths include:
- Shellfish.
- Annelled worms.
- Sipunculids are worm-like marine animals that have a rudimentary circulatory system, an excretory system, and a loop-like intestine with an anus from the back.
- Echiurids - organisms living in sea waters. They have a cylindrical body with a proboscis. The mouth opening is located on the peritoneal side. They are distinguished from other representatives by the presence of an underdeveloped circulatory system and a tubular intestine, which ends with an anus.
- Pentateurs or reeds, which are worm-like parasitic invertebrates with a tongue-shaped body similar to arthropods.
- Onychophorans or primary tracheal - are represented by terrestrial predators, on a long body of which there are up to 43 pairs of legs.
- Tardigrade - small organisms with four pairs of limbs.
- Arthropods.
Deuterostomes, or deuterostomes, are represented by the following types of animals:
- Bristles;
- semi-chordates (supra-intestinal and pterygobranch);
- echinoderms;
- pogonophores;
- chordate;
- graptolites (fossils).
The stages of development of deutorostom are incomprehensible. It is assumed that their evolution began with multicellular invertebrates, which in no way intersect with protostomes. Others believe that the ancestors of protostomes are lower worms, which are classified as primitive types of protostomes.
What is the difference between protostomes and deuterostomes
In addition to the formation of the inlet, represented by the mouth, deuterostomes and protostomes differ in a number of other characteristics:
- According to a series of divisions of eggs: in the first they are radial, directed along the radial, and in the second - spiral (uneven).
- Methods of laying coeloms (cavities): in protostomes, the development of the walls of secondary cavities begins with cell division, and in protostomes, they are formed from protrusions of the pockets of the intestines of the embryo.
- The subsequent genesis of the brain: in protostomes, it develops into an adult state, and in the second, it decreases and is laid in a new area.
Therefore, deuterostomes are also called secondary brain creatures.
Scientists believe that deuterostomes and protostomes have one common ancestor that lived in the Edikar Sea more than 500 million years ago. The creature's habitat was the seabed, along which it moved, working with cilia located in a strip on the abdomen, and fed through the tentacles with which it picked up food. Perhaps later, the back part of the body became isolated and the progenitors of deuterostomes used it to burrow into the soil layer for a while.
Deuterostomes and protostomes are similar in development and structure. But they also have a number of differences that make their followers different from each other.
