The peculiarity of second-rooted animals is thatthat during the development of the embryo, the formation of the anus occurs at the site of formation of the primary mouth, and the mouth subsequently appears in a completely different place. In other words, the germ can be said to have an oral opening at one end, and an adult in the opposite place. Secondary animals belong to the realm subsection, which includes echinoderms, chordates, and semi-chordates. They are referred to the so-called bilateral-symmetrical living organisms.
Features of bilaterally symmetrical animals
The main feature of such animals is thatthat the left and right sides of their body are clear mirror images of each other. How to understand this? You just need to imagine a plane that sort of divides the body of an animal in half. In this case, both of these parts will be exactly the same. In some sources you can find the concept of "two-sidedly symmetrical" animals.
This feature completely distinguishes this species fromother representatives of the fauna and man whose body is conditionally symmetrical. This means that not all organs are located in the same plane. And the bilaterally symmetrical other planes do not. This feature has positive points. Such animals are very easy to move in straight lines and rotate. These include primary and secondary animals.
Difference of primary and secondary
Representatives of these species, though similar,there are differences. As mentioned above, primary-bred and secondary-bent animals belong to the bilaterally symmetrical one. These names derive from how their oral opening develops during embryonic development. In primary fungi, a transition of the blastospore occurs (a hole in the primary intestine) into the formation of the oral cavity. And for those who are secondary in this place, the anus is formed. When this mouth is formed in a new way at the front end of the embryo. There are also examples when the blastopore is completely closed, and the mouth and anus reappear.
And another important difference is the developmentprimary brain. The primary mover develops the brain of an adult animal. In secondary cases, its reduction occurs, and a new one is formed again in another place. Secondary animals are also called secondary cerebral animals.
Classification of Secondary Animals
Above, we looked at who the secondary animals are, examples and features of their development. Now it's time to find out who belongs to this subregion. These include the following types:
- chord;
- bristle teeth;
- echinoderms.
Now let's take a closer look at whatanimals belong to secondary-short animals. Chordates include lancet, lamprey, fish, amphibians, reptiles, birds, and mammals. Marine animals are the bristles of the jaws, the most famous of which is the sea arrow. A very unusual type of echinoderms includes sea stars, sea urchins, sea cucumbers, sea lilies. All of these representatives of the fauna are united by the fact that they are secondary-rooted animals. In addition to the characteristics of the formation of the oral cavity, these creatures also have differences in the development of other organs and systems.
Features of the development of the embryo chord
Chordates are secondary animals that arediffer in appearance, manner and conditions of life. Representatives of this type can be found everywhere. They live on land, in water, in soil, and in the air. Distributed throughout the globe. The number is about forty thousand.
Unites them all the presence of an axial skeleton,which at the developmental stage of the embryo is represented as a dorsal string (chord). In adult individuals, in unchanged form, it remains only in the lower representatives of the type. For all the others, it goes into the formation of a spinal column, which goes from a continuous strand into a segmented one.
The method of crushing a fertilized egg is also a distinctive feature between these two sub-kingdoms: the spiral one at the primary turn and the radial one at the secondary turn.
The nervous system is a hollow tube, the front of which later becomes the brain. From the internal cavity formed his ventricles.
In the anterior digestive tubethere are two rows of holes through which communication with the external environment takes place. This is the so-called visceral gap. Lower chordates in this place have gills. All the others have only germinal rudiments, which subsequently do not function.
Some sources refer to secondary socalled semi chord. These are worm-like bottom animals. Characterized by the presence of notochorda (chord-like organ) and paired gill slits. In the embryonic development they resemble chordates, but the structure of the body is completely different. The body is represented by three sections: the proboscis, the collar and the trunk.
Brush Animals
Эти животные являются морскими хищниками, able to move fast. Outwardly, they look like an arrow, which is pointed from the front end, and has a tail at the rear. These are the very bristles with which the animal captures food. The body is made up of the head, torso and tail. There are paired lateral and one caudal fins.
The belonging of these animals to secondaryconsists in embryonic development of the oral cavity and in that the egg is crushed radially. In all other respects there are a number of differences. These animals do not have circulatory, respiratory and excretory systems. There are also no genital ducts. The nervous system is a pharyngeal ring.
Features of echinoderms
Characteristic feature of this representativestype is the presence of the ambulacral system. These are cavities filled with liquid, thanks to which the animal moves, breathes, perceives and produces excretory processes.
The intestine is a long tube orbag. The circulatory system is represented by annular and radial vessels. Decay products are released through small pores in the walls of the body. The sense organs and the nervous system are poorly developed. But regenerative abilities are well developed. In case of danger, these animals can discard separate parts of the body, which are restored in two weeks. Thanks to this feature, starfish can even multiply by dividing in half. After a while the second half is fully restored.
Outcomes
From the above, you can find out whichanimals belong to the secondary, about the features of their development and representatives of this sub-kingdom. Obviously, the representatives of this species are very interesting. Their research is still ongoing.
