List ancient signs in modern cartilaginous fishes. Their features

Within the framework of this article, it is necessary to list the ancient signs in modern cartilaginous fishes. These include stingrays and sharks. It is about them that will be further discussed.

Sharks and rays: a general characteristic

As noted earlier, this is a class of fish, a group of cranial, with bright representatives of rays and sharks. Several dozen species of this class belong to the remnants of ancient groups. As previously assumed due to the absence of bone skeleton does not make them a group of prehistoric animals. But for a number of signs, such a connection exists.

List of ancient signs

First, they have such a feature as the lack of a swim bladder. Secondly, they do not have gill covers and the gills themselves have a primitive structure. All gill slits, in turn, open outward with an independent opening. All these features are characteristic of ancient fish. In this regard, they are forced to be in constant movement. The circulatory system should work more effectively, the heart has the form of an arterial cone, which increases the efficiency of blood circulation. But the feature of sharks is a powerful muscle body, which helps to pump blood throughout the body, since the heart of sharks is not adapted to heavy loads.

It is necessary to list the ancient signs in modern cartilaginous fishes even further. Thirdly, this anatomical structure of the body reduces the frictional force of water, which increases the speed of movement. In addition, the secret secreted by them prevents the attachment of parasites to the body of the fish and to some extent protects them from certain types of bacteria.

Fourthly, the cartilaginous fish mouth is located transversely, which is typical for ancient fish, in the anterior part, which is the base of the snout (rostrum), cartilage is formed, this structure is characteristic, for example, for sharks. Fifth, the body is covered with placoid scales.

Sixth, in full, it is impossible to list the ancient signs in modern cartilaginous fish in full, if one does not take into account their peculiarity of reproduction. Due to it, they are more adapted to the conditions of existence than, say, bony fish, which throw out an unprotected game to the mercy of fate. A large part of the eggs remains unfertilized. In most sharks and rays, the embryo's body is connected to the mother through a certain "child's place", which is similar to the placenta of mammals. Or they lay off large eggs, clad in thick shells, immerse them in sand.

The internal structure of fish of this class

Let's talk about the internal structure of fish, which can be carried to the cartilaginous class, the bright predator and representatives of this class, like a shark.

The muscular system of sharks consists of myomers, is developed. Myomers are muscle segments. The musculature is abundantly supplied with blood, because for a shark the movement is life. In order for the shark's blood to return to the heart, only the pressure created by the heart itself will not be enough. The absence of urinary tract and kidney is a feature of the internal structure of these representatives (in particular, the polar shark). Toxins are washed out by the blood and are released outside simply through the skin of a predator. Gill slits located on the surface of the body and open outward and into the pharynx. As described above: the shark does not have a swimming bladder, this feature is attributed to the above listed ancient features of modern sharks and rays. In addition to its main function, the liver partially performs the functions of a swim bladder. The dimensions of the liver are significant. Also partially this function was assumed by the pancreas and gall bladder.

Conclusion

So, we described and listed the ancient signs of modern cartilaginous fishes, outlined the features of the structure and adaptation to habitation in the external environment, similar to the ancient fish.