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Skeleton. The axial skeleton of fishes has various structure. At ancient groups of fishes (himerovy, sturgeon and amphipneustic) it is presented by the chord dressed by dense covers, and cartilaginous or bone arches of vertebras, and bodies of vertebras are not present. At younger modern cartilaginous and bony fishes the axial skeleton is presented by a cartilaginous or bone backbone where between bodies of vertebras the chord remains remain. The backbone consists of separate vertebras with the biconcave (amfitselny) bodies, the top arches forming the spinal channel, and the lower arches forming edges in tulovishchny department or the gemalny channel in the tail.

Organs of smell. Play at fishes large role at food. At all fishes, except for amphipneustic, organs of smell have a form of pair bags with folded walls and open outside of one or two nostrils.

The swimming bubble and lungs develop protrusion of back part of a throat and, apparently are homologous to the last branchiate bag, but each other lungs and a swimming bubble are not homologous since the first are formed of belly part of a branchiate bag, and the last – from its back part.

The scales of fish always are derivative actually skin (the corium, and only sometimes, except a corium, takes minor part and epidermis in its education. Distinguish four main types of fish scales: plakoidny, kosmoidny, ganoidny, bone.

And if the fair portion of spirit of the researcher is added to it, on the foreground the aspects of training and assimilation following from active occupations of the akvriumistiky act. In the conditions of limited space it is obviously possible to make numerous observations over behavior of fishes and to analyze it.

Skeleton of extremities. Both humeral, and pelvic belts are not jointed with a backbone, and lie freely among muscles. For all bony fishes connection of a humeral belt with a skull by means of a number of skin integumentary bones is characteristic. At last, it is characteristic that unpaired fins too have a skeleton.

Cartilaginous fishes are deprived of bones, and their internal skeleton consists entirely of a cartilage. They share on two unequal groups: on big group plastinozhaberny, or akulovy, the fishes who kept a primitive structure of a skeleton, but having more perfect structure of bodies of reproduction and nervous system and on not numerous chimeras, or tselnogolovy at which top jaw, having merged with a cranium, got the special durability necessary at crushing of sinks of the mollusks serving as it the main food.

It is widespread and numerous group of fishes. They live in waters of Europe, Asia, Africa and North America. Are characterized by lack of teeth on jaws and existence, except for Girinokheylov, teeth on pharyngeal bones. Mouth, as a rule, the sliding.

Includes 31 families with 373-375 childbirth and more than 1200 types. Somovidnye have no real scales, their body or naked, or it is covered with the bone plates sometimes having an appearance of shipik, and the mouth has moustaches which are organs of touch. Live on all continents.

Skull. Fishes it is characterized first of all by strong development of visceral department which contains the maxillary device consisting from maxillary and hypoglossal (gioidny) arches and the branchiate device from a number of branchiate arches in number of not less than 5 (at their some sharks happens 6 and even the gills sitting on them.

Includes 6 families of fresh-water fishes to which about 1,5 thousand types belong. The shape of their body is various, but the general for all fishes is existence of the fatty finlet located between back and tail fins and which is not containing beams.