A feature of deuterostomes is that during the development of the embryo at the site of the formation of the primary mouth, the formation of the anus occurs, and the mouth subsequently appears in a completely different place. In other words, we can say that the embryo has a mouth opening at one end, and the adult in the opposite place. Deuterostomes belong to a subsection of the kingdom that includes echinoderms, chordates, and hemichordates. They are classified as so-called bilaterally symmetrical living organisms.
Features of bilaterally symmetrical animals
The main feature of these animals is that the left and right sides of their bodies are clear mirror images of each other. How to understand it? You just need to imagine a plane that, as it were, divides the body of the animal in half. In this case, both of these parts will completely coincide. In some sources, you can find the concept of "bilaterally symmetrical" animals.
This feature completely distinguishes this species from othersrepresentatives of fauna and humans, in which the body is conditionally symmetrical. This means that not all organs are placed in the same plane. But bilaterally symmetrical other planes do not. This feature has positive aspects. Such animals move very easily in straight lines and turn. These include protostomes and deuterostomes.
The difference between protostomes and deuterostomes
Representatives of these species, though similar, but there are still differences. As mentioned, bilaterally symmetrical animals include protostomes and deuterostomes. These names come from how their mouth opening develops during embryonic development. In protostomes, the transition of the blastospore (an opening in the primary intestine) into the formation of the oral cavity occurs. And in deuterostomes, the anus is formed in this place. In this case, the oral opening is formed in a new way at the anterior end of the embryo. There are also examples when the blastopore is completely closed, and the mouth and anus reappear.
And another important difference lies in the development of the primary brain. Protostomes develop the brain of an adult animal. In deuterostomes, it is reduced, and a new one is formed again in another place. Deuterostomes are also called secondary brains.
Classification of deuterostomes
Above we examined who deuterostomes are, examples and features of their development. Now it's time to find out whobelongs to this sub-region. This includes the following types:
- chordates;
- chaetognaths;
- echinoderms.
Now let's look in detail which animals are deuterostomes. Chordates include lancelets, lampreys, fish, amphibians, reptiles, birds, and mammals. The chaetognaths are marine animals, the most famous representative of which is the sea arrow. A very unusual type of echinoderm includes starfish, sea urchins, holothurians, sea lilies. All these representatives of the fauna are united by the fact that they are deuterostomes. In addition to the peculiarities 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 of chordates
Chordates are deuterostomes that differ in appearance, manner and living conditions. 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.
They are all united by the presence of an axial skeleton, which at the stage of embryo development is represented as a dorsal string (chord). In adult individuals, it remains unchanged only in the lower representatives of the type. For all the rest, it passes into the formation of the spine, which turns from a continuous strand into a segmented one.
The method of crushing the fertilized egg is also a distinguishing feature between these two sub-kingdoms:spiral in protostomes and radial in deuterostomes.
The nervous system is a hollow tube, the front of which later becomes the brain. His ventricles are formed from the internal cavity.
In the anterior part of the digestive tube there are two rows of holes through which communication with the external environment takes place. These are the so-called visceral gaps. The lower representatives of chordates in this place have gills. For everyone else, these are only embryonic rudiments, which subsequently do not function.
Some sources classify the so-called hemichordates as deuterostomes. These are worm-like benthic animals. They are characterized by the presence of a notochord (chord-like organ) and paired gill slits. In embryonic development, they resemble chordates, but the body structure is completely different. The body is represented by three sections: proboscis, collar and torso.
Bristle-jawed animals
These animals are marine predators with the ability to move quickly. Outwardly, they look like an arrow, which is pointed at the front end, and has plumage at the back. These are the very bristles with which the animal captures food. The body consists of the head, trunk and tail. There are paired lateral and one tail fins.
The belonging of these animals to deuterostomes consists in the embryonic development of the oral cavity and in the fact that the egg is crushed radially. In all other respects there are a number of differences. These animals do not have circulatory, respiratory and excretorysystems. There are also no genital ducts. The nervous system is a ring around the pharynx.
Features of echinoderms
A characteristic feature of representatives of this type is the presence of an ambulacral system. These are fluid-filled cavities that allow the animal to move, breathe, touch, and excrete.
The intestine is a long tube or bag. The circulatory system is represented by annular and radial vessels. The decay products are released through small pores in the walls of the body. Weakly developed sense organs and nervous system. But regenerative abilities are well developed. In case of danger, these animals can discard individual parts of the body, which are restored after two weeks. Thanks to this feature, starfish can even reproduce by dividing in half. After a while, the second half is fully restored.
Results
From the foregoing, you can find out which animals belong to deuterostomes, about the features of their development and representatives of this sub-kingdom. Obviously, representatives of this species are very interesting. Their research is still ongoing.
