Cartilaginous fishes, bony fishes: characteristic, structure, differences

According to the latest scientific data, the ancestors of modern fishes - wild-blooded animals resembling their appearance - lived already in the early Cambrian, about 530 million years ago. It is suggested that similar creatures found in 1999 in Yunnan province can be the progenitors of all vertebrates.

At the moment, cartilaginous fishes, bony fishes (lobateperes and luchepers) account for more than half of all vertebrate animals living on the planet. In total, there are about 31 thousand species of a variety of shapes, sizes, living in salty and fresh water. The study of ancient creatures is a separate science - ichthyology. Let us dwell in more detail on the classes, their features and differences.

Cartilaginous fish

The main feature of all the representatives of the class is that their skeleton consists of cartilages, which with time as a result of the deposition of minerals can become quite hard. Earlier for this reason, they were considered prehistoric animals. However, many of them are characterized by live birth, sometimes even with the formation of the bile placenta - this is what cartilaginous fish differ from bone fish cardinally.

In addition, they have several more anatomical features of the structure. First, the absence of a swim bladder. Therefore, they have to move in order to descend to the bottom of the reservoir. Secondly, cartilaginous fishes have no gill cover, and the gills open outward with characteristic gaps. Thirdly, they are all covered with placoid scales, which is similar to the teeth of vertebrates. It consists of dentin and enamel covering it. Such scales are not restored with loss, but with the growth of fish its quantity increases.

Life support systems in cartilaginous fishes

Characteristics of cartilaginous and bone fish will not be complete, if not to mention the main systems: the circulatory, digestive and sexual, in which there are differences. Cartilage has red blood (due to the presence of hemoglobin and erythrocytes), which is produced by the spleen. The circulatory system itself resembles that of the cyclostomes. Along the spine stretch in the form of two dark red bands of the kidney. The intestine of the cartilaginous fishes consists of three parts: it is a thick and small intestine, rectum. The liver and pancreas are well developed. But the most important thing is that the classes of cartilaginous fish and Bony fishes differ in the structure of the reproductive system. The first is characterized by internal fertilization with the formation of an egg, which can be deposited in the external environment or remain in the lower part of the oviduct. In the second case, the embryo begins to develop in the maternal body.

Classification of cartilaginous fishes

All of the existing representatives of the class Cartilaginous fish are divided into three supernumeraries.

• Skates are cartilaginous fishes (bony fishes - hereinafter) with a characteristic "flattened" body shape and large pectoral fins fused with the head. Scales are reduced in many of them, One of the largest representatives is manta.
• Sharks. Fish, which have such distinctive features: a torpedo-shaped body, an elongated, heterocercal large caudal fin and a large number of teeth on the jaws. One of the oldest representatives on Earth, whose ancestors appeared 420-450 million years ago. Sizes range from 17 cm to 20 m (whale shark - in the photo above), most predators. Each species has a certain lifespan, but in most cases they are longevity - 20-30 years.
• Tselnogolovye - represented only one unit - Chimera, which includes about 50 mostly deep-sea fish. This explains their small study.

Bony fish: a general characteristic

For a long time, up to the 21st century, cartilaginous fishes, bony fishes were considered as two classes. However, in a scientific environment, another point of view is gaining wide acceptance. Thus, the Canadian zoologist in his works of lobe-hoppers and ray-finned fishes defines into separate classes, and bone, respectively, into the superclass. This is the most diverse inhabitants of all types of reservoirs. Their mouths are formed by grasping jaws and teeth located on them, gills are located on branchial arches, and nostrils are paired.

Differences from cartilaginous fishes

The most important difference between bone fish and cartilage is clear from the name - the skeleton. He's made of bones. In the internal cavity are circulatory system, secretion, reproduction and digestion. Scales are also characteristic, one of three types: cycloid, ctenoid or ganoid.

The next difference is the presence of a swim bladder located under the spine and filled with gases that secrete blood vessels. With an increase in its volume, the fish easily floats to the surface, with a decrease - it goes to the depth.

Differences are not only external signs of cartilaginous and bony fishes, but also reproductive organs, as already mentioned. For the majority of representatives of the second group, external fertilization occurs in the aquatic environment. This process was called spawning, it occurs at certain times and is accompanied by characteristic behavior.

Lacerated fish

This is a numerically predominant class in the modern variety of fish, they number more than 20 thousand species, which is about 95%. They populate all corners of the planet, from the arctic seas to the hot equator, the sizes range from 8 mm to 11 meters, and the weight of individual individuals reaches more than two tons. The name, as is not hard to guess, is associated with the structure of paired fins, in which there is no basal axis. The class, in turn, is divided into two groups: Novopyerye (the most prosperous species) and Kostochkryshchevye fish. The structure of the latter has distinctive features. They have a swim bladder, but at the same time their skeleton basically consists of cartilaginous tissue. Chorda has only cartilaginous arcs and is not dissected, vertebral bodies as such are absent. A distinctive feature - rostrum and lower mouth. Many of them are commercial, in particular sturgeon (in the photo below - catch of beluga).

Lopastegre fish

A small class of fish, the skeleton of which is based on an elastic chord. They combine progressive and archaic traits, all representatives belong to two modern order-holders - Kystepery and Dvojkoyyshyshye. Both groups unite ancient fish. Lung frogs live in fresh water bodies of Australia, South America and Africa. They possess not only gills, but also lungs. This allows them some time to do without water and feel free to deplete oxygenated reservoirs. In total, 6 species are known: four African protopters (photo below), Australian bastard and South American scaly cat.

Nadotryad Kistepery

It is considered almost extinct. Up to now, only one genus has arrived - the Latimiria (pictured below), which has two species. And both of them were discovered relatively recently, the first specimen was caught in the Indian Ocean in 1938. It is believed that cystepper fish are the inhabitants of fresh water reservoirs in which there was a lack of oxygen. In this regard, they developed a musculature at the base of the fins and a double way of breathing (lungs and gills). This allowed some to move back to the seas, and the freshwater eventually died out. There is an assumption that it was precisely the cystpie fish that gave rise to the class of Amphibians.

Thus, cartilaginous fish, bone fish have a number of individual characteristics. The main ones are observed in the structure of the skeleton (cartilaginous or bony), the presence or absence of a swim bladder, the type of scales, the reproductive system and the method of reproduction.