When describing the development of living organisms oftenYou can come across the terms "primary movers" and "secondary moles". These are all existing multicellular, except for intestinal cavities, which differ at the embryonic level.
The development of chordates
Chordates are represented by three groups of organisms:
- tunicates, or larval-chord tunicates (Tunicata, Urochordata), which have a bag-shaped body enveloped in a shell;
- uncranial, or golovokhordovyh (Acrania), living in the deep sea fish-like slow-moving creatures;
- vertebrates - representatives of fish, amphibians, snakes, birds, animals and humans.
The story of the birth of chord shroudedmystery and causes many assumptions. And in order to concretize them, it is necessary to figure out who the secondary and primary-rotating animals are. It is authentically known that more than 500 million years ago there already existed golovokhordovye. The preceding stages remain enigmas, therefore various hypotheses of the origin of living beings arise.
The essence of primary and secondary animals
Многоклеточные представляют царство Животные.Primary and short - their direct ancestors. Their verbal designations Protostomia and Deuterostomia are formed from the characteristics 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 at a new location.
Classification of bilaterally symmetric organisms
Secondary and primary animals have their own classifications. To primary turnover include:
- Shellfish.
- Ringed worms.
- Sipunculides - worm-like marine animals, which have revealed the presence of a rudimentary circulatory system, excretory system and loop-like intestine with anus from the back.
- Ehyurids are organisms that live in marine waters.They have a cylindrical body with a proboscis. The oral opening is located on the peritoneal side. The presence of an underdeveloped circulatory system and a tubular intestine, which ends in the anus, distinguishes them from other representatives.
- Pyatiustkov or reed, which are worm-like parasitic invertebrates with a tongue-like arthropods.
- Onykhoforov or primotracheynyh - represented by land predators, on the long body of which there are up to 43 pairs of legs.
- Slug - small organisms with four pairs of limbs.
- Arthropods.
Secondary animals, or deuterostomas, are represented by the following types of animals:
- bristle teeth;
- poluchordovye (nadkishechnodyshyshie and krylazlabernye);
- echinoderms;
- pogonophora;
- chordates;
- graptolites (fossils).
Этапы развития дейторостом непонятны.It is assumed that their evolution began with multicellular invertebrates, which in no way intersect with primary rot. Others believe that the ancestors of the secondrota are lower worms, which are classified as primitive types of primordial.
What is the difference between primary and secondary
In addition to the formation of the inlet, represented by the mouth, secondary and primary-necked animals differ in a number of other characteristics:
- For a number of egg divisions: in the first they are radial, directed along the radial, and in the second - spiral (non-uniform).
- Ways of initiating coeloms (cavities): in primary motility, the development of the walls of the secondary cavities begins with cell division, and in secondary movers, the protrusions of the intestinal pockets of the embryo are formed.
- The subsequent genesis of the brain: in primary moles, it develops into an adult state, while in the second it decreases and is laid in a new area.
Therefore, the secondary people are also called secondary cerebral beings.
Ученые считают, что вторичноротые и первичноротые animals have one common progenitor, who lived in the Edikar Sea more than 500 million years ago. The creature’s habitat was the seabed, on which it moved, working with cilia arranged in a strip on the abdomen, and ate by means of the tentacles with which it picked up food. Perhaps later, the back of the body became isolated and the progenitors of the secondary ones used it to temporarily dig in the soil layer.
Secondary and primary animals are similar in development and structure. But they also have a number of differences, so that their followers differ from each other.
