The structure of the river cancer: external and internal

The structure of the river cancer, which is representative of the arthropod type, is associated with its habitat. It is a typical inhabitant of fresh water bodies, which breathes with the help of gills. In this article, river cancer will be considered. The structure, pictures, habitat and life features are presented below.

Characteristic features of crustaceans

Like all arthropods, the structure of the river cancer (the figure below shows it) is represented by a segmented body and limbs. This is the head, chest and abdomen. Segments of the body carry paired extremities, consisting of separate segments. They are able to make quite complex movements. Articular extremities usually attach to the thoracic segments of the body. The external structure of the crayfish completely corresponds to the characteristic features of arthropods.

Habitat

River crayfish can be found in fresh water. And their availability can be considered an indicator of its environmental safety. After all, these animals prefer water with clear water and high oxygen content. The structure of the river cancer determines their ability to crawl with walking legs or swim. During the day they are in natural shelters. At night they crawl out of holes, from under stones and logs. At this time they are looking for food. In this regard, crayfish are not choosy. They are generally omnivorous. Worms, fry, tadpoles, mollusks, algae - all of them will taste like river crayfish. They do not disdain the dead organic. If you decide to have this animal in your home aquarium, not only special food, but meat, vegetables and bread will suit you. True, while maintaining the purity of water will be quite difficult.

External structure of the river cancer

The body of crayfish consists of two parts. This is the cephalothorax and abdomen. The front part is covered with a so-called shell. And the abdomen consists of separate segments, on top of which are located small scutes. The cephalothorax also contains two pairs of antennae, a mouthpiece and five pairs of walking legs. Each of them performs certain functions. For example, the first pair ends with powerful claws, serving to grab food, tear it to pieces and protect it from enemies.

Six pairs of limbs are attached to the abdomen. The last pair of legs is enlarged and forms a caudal fin along with the anal plate. In appearance, it resembles a fan. With the help of the anal fin, the crayfish quickly swim the posterior end rather quickly. Together they have 19 limbs.

Covers of the body

The peculiarities of the structure of the river cancer are determined primarily by its cover. Like all arthropods, it is represented by a cuticle, which forms a powerful outer skeleton. An additional hardness is given to calcium carbonate, which it is impregnated with.

Since the cuticle is not capable of stretching, the growth of crayfish is accompanied by periodic molts. This period is critical in the life of these aquatic inhabitants. A few days before, the crayfish became restless, stopped eating, and all the time spent in search of shelter. With the help of intensive movements of the body and limbs, they get rid of the old cover, from which they get out through the gap on the border of the cephalothorax and abdomen. In their reliable shelter, the crayfish remain up to ten days, until the new cuticle hardens.

Internal structure of the river cancer

During embryonic development, a secondary body cavity is laid in all arthropods. But it does not persist throughout the life of the animal. In the process of individual development this structure collapses, merging with the remnants of the primary and forming a mixed cavity. Spaces between organs are filled in crustaceans with fatty body. This is a kind of loose connective tissue that performs important functions: the storage of nutrients, the formation of blood cells, protection from mechanical damage.

Musculoskeletal system

The structure of the river cancer significantly differs from the structure of mollusks and coelenterates. In particular, they do not have a skin-muscular sac. Under the strong outer skeleton there are bundles of striated muscles, capable of rapidly contracting.

Basic organ systems

The internal structure of the river cancer is represented by rather complex systems of organs. Digestive - an end-to-end type, with the presence of the liver and salivary glands, which secrete enzymes that break down nutrients. The final products of metabolism are removed from the body with the help of excretory system, represented by Malpighian vessels.

The respiratory organs of the river cancer are caused by the aquatic environment of its habitat, these are the gills. The blood system is closely connected with them. It is not closed. Blood vessels open into the body cavity, mix with its fluid, forming a hemolymph. It carries out transportation of oxygen, carbon dioxide, nutrients, exchange products.

The most important function of the hemolymph is the protective function. It contains specialized cells that carry out amoeboid movements, seize pathogenic microorganisms by pseudopods and digest them. Movement of the hemolymph in the body provides a pulsating thickened vessel - the heart. Because the blood mixes with the cavity fluid and is not divided into arterial and venous, the river cancer is a cold-blooded animal. This means that the temperature of his body goes down with a cooling in the environment.

In late autumn, crayfish begin to multiply. These are dioecious animals with direct development and external fertilization. The male has a testis and two vas deferens, the female has an ovary and paired oviducts. After fertilization, the eggs are on the abdominal legs of the female. So she shows the maternal instinct, caring for the future offspring. At the end of spring or early summer, young crustaceans emerge from them, which are an exact copy of adult individuals.

The nervous system is also quite complicated. It consists of differentiated sections: front, middle and back. The first regulates the work of the eyes, provides complex behavioral responses of these animals, the rest innervate the antennae. The brain is anatomically connected to the abdominal neural chain, from which separate nerve fibers leave the body.

Significance in nature and human life

Young individuals of the river cancer form a plankton of fresh water bodies - an important link in the food chain. Using the dead animals to eat, they clean the habitat. Recently, due to the negative influence of humans, the number of populations of river cancer has dramatically decreased. In the dirty water the offspring of the river cancer inevitably awaits death. This is also due to the important commercial significance of this representative of the arthropods. After all, meat of river cancer is a valuable food product, and in some regions even a delicacy. It is rich in proteins, vitamins and trace elements. River cancer is the largest representative of the class that lives in fresh water. To keep this species in nature, until the middle of summer, their fishing is officially banned.

The structure of river cancer is largely due to its habitat and determines its importance in nature and human life.