What is different from other cartilaginous fish? Class Cartilaginous fishes: description, examples

Some of the most interesting aquatic animals are fish. Class Cartilaginous fish - sharks and rays - have significant differences from other representatives of this superclass.

The Fish Superclass

This group of animals has absolutely all the devices for a comfortable life in fresh and salt water. First of all, it is a streamlined body shape that allows you to move without difficulty. Their body is covered with scales. It protects fish from the friction of water and helps to slide in it. The skin gives off a lot of mucus, being an additional protection. Fins - this is a kind of steering wheel, determining the ability to move. And the gill respiration, which allows the release of oxygen from the water, finally determines the habitat of these animals.

Just a unique combination of features of the structure have fish. Class Cartilaginous fish and Bony are two classes of these organisms. Despite a single habitat, they have both similar and excellent features of the body.

External structure of fish

All fish, class Cartilaginous fish and Bone, have the same body parts. This is a fixed head, trunk and tail. On the front part are the eyes, mouth and nostrils.

The body of fish is covered with scales, which are derived horny skin formations. By increasing its layers it is easy to determine the age of the animal. This process can be compared with the formation of annual rings on tree trunks. After all, scales cease to grow in winter, but resume this process with the onset of spring.

If you describe the shark, then you need to point out the presence of gill slits on the body of the fish. The same formations are found in skates as well. Unlike other fish, in which the gills are covered with lids.

Internal structure of fish

All features of anatomy correspond to the aquatic mode of life of these animals.

All bones of the skeleton are divided into 3 parts: head, trunk and fins. The skull serves as a reliable defense of the brain. It includes bones of gill covers and arches. Vertebrae, consisting of the body and arcs, form a channel in which the spinal cord is located. The skeleton of the fins consists of rays, to which the muscles join, leading the fins into motion.

All fish, cartilaginous including, have a similar structure of the digestive system. It is represented by a mouth opening, oropharyngeal cavity, esophagus, stomach and intestine. In cartilaginous fish, the intestine ends with the anus, while in the bony ones it ends with a cloaca. Digestive glands - pancreas and liver - secrete their enzymes into the small intestine ducts.

The organs of excretion are represented by the kidneys - paired ribbon-like organs, in which the products of metabolism accumulate, through the ureters coming out.

Breathe fish with the help of gills that are capable of releasing oxygen from the water. They consist of arcs and petals. In bone fish respiratory movements are carried out with the help of gill covers. In cartilaginous organs, the respiratory organs open outwards with slits - 6-7 pieces on each side.

A rare group of aquatic animals - double-digging fish - in addition to the gills, there is an additional lung. But they can not live on land. The lung connects with the esophagus, allowing them to dwell in water bodies with a low oxygen content.

The circulatory system is represented by a two-chambered heart and a closed system of blood vessels. All fish are cold-blooded animals. This means that the temperature of their body depends on the environment.

The nervous system consists of the brain and spinal cord. In the first of these, one can especially single out the development of the cerebellum, which determines the complex movements of fish.

The eyes of the fish allow them to distinguish only the outlines of objects at close range. And the main role among the sense organs of fish is performed by the lateral line, by means of which they perceive the fluctuations of water and its speed.

Bone fishes

They are the overwhelming majority of these aquatic animals. Bony fishes are characterized by the presence of four main features:

• Bone skeleton;
• Presence of a swim bladder;
• Gill covers;
• The skin is completely covered with scales.

The swelling bladder is an esophagus with thin walls, filled with gases. Due to its presence, the specific weight of fish decreases. This helps her to easily keep in the water column. In addition, with a lack of oxygen in the water, a certain volume can pass from the swim bladder into the blood.

Signs of cartilaginous fish

But this group of animals, on the contrary, has a cartilaginous skeleton and gill slits instead of lids. Cartilaginous fish are devoid of a swim bladder. This determines the way of life and habitat. Thus, skates lead a benthonic lifestyle, and sharks are constantly in motion.

Their biology is very interesting. Cartilaginous fish, unlike bone, are not completely scaled. It is located on their body in separate rows and is formed by a strong substance - dentin. Outwardly the scales of cartilaginous fishes resemble denticles.

Which fish are cartilaginous? They are mostly predatory. Therefore, their teeth are arranged in several rows. Sharks do not chew food at all. They grab their prey, tear it up and swallow it whole.

Pectoral fins in cartilaginous fishes are located in a horizontal plane. Therefore, their movements in the water resemble the soaring flight of birds.

Scary predators

The description of the shark will terrify any, even the most courageous person. And those who survived a meeting with a predator, hardly want to remember about it. And this is not accidental.

Sharks are absolutely indiscriminate in food. And although some of them like to eat plankton, most prefer a larger treat.

Systematists know about 250 species of sharks. But the largest and most dangerous of them are the whale and giant, whose body length can reach 15 meters.

If the majority of fish are characterized by external fertilization, some species of sharks are ovivivorous. Caviar is retained in the female organism, and after internal fertilization a young individual develops from it, which is completely viable.

Ramps

At first glance, these calm benthic representatives of cartilaginous fishes present no threat to others. But the rays are predators, hunting for mollusks, echinoderms and crustaceans.

In nature, more often there is a marine stingray, but freshwater species also exist. Among the species of rays is a tail, electric, manta ray, smooth.

Their appearance can not fail to impress. The body is flattened in the dorso-ventral direction. Fins fuse with it, which determines the name of this group of animals, which means "cloak".

The size of the body is also impressive. For example, the length of the sea devil (manta) can exceed 6 meters, the wingspan - up to 3. And they can weigh as much as 2 tons.

It is also interesting that skates can fly. Not like birds, of course. But, jumping out of the water at 1.5 m, they create exactly this impression.

Importance of cartilaginous fish

In the economic activity of man a special place is occupied by fish. The class of cartilaginous fish not only represents a certain threat. From the skin of sharks make bags and wallets. Their meat has valuable nutritional properties, and fat is a source of vitamins and trace elements.

The sea slope is also an object of fishing. But many of them are dangerous for humans. The impact of the tail can lead to death, and the impact of the electric ramp is paralyzed.

Cartilaginous fish are amazing representatives of aquatic animals, which play an important role in the formation of food chains and are the object of artificial breeding.