The structure of crayfish, which is a representative of the type of arthropods, is associated with its habitat. This is a typical freshwater inhabitant that breathes through gills. This article will examine crayfish. The structure, pictures, habitat and features of life are presented below.
The characteristic signs of crustaceans
As with all arthropods, the structure of crayfish (the figure below shows it) is represented by a segmented body and limbs. This is the head, chest and abdomen. Body segments carry paired limbs, consisting of separate segments. They are able to make fairly complex movements. Jointed limbs usually attach to the thoracic segments of the body. The external structure of river cancer is fully consistent with the characteristic features of arthropods.
Habitat
Crayfish can be found in fresh water. Moreover, their presence can be considered an indicator of its environmental safety. After all, these animals prefer ponds with clean water and high oxygen content. The structure of crayfish determines their ability to crawl with walking legs or swim. In the afternoon 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 picky. They are generally omnivores. Worms, fry, tadpoles, mollusks, algae - all of them will appeal to crayfish. They do not disdain dead organics. If you decide to get this animal in your home aquarium, not only special food is suitable for food, but also meat, vegetables and bread. True, it will be difficult to maintain clean water.
External structure of crayfish
The body of crayfish consists of two parts. This is the cephalothorax and abdomen. The front part is covered with the so-called carapace. And the abdomen consists of separate segments, on top of which there are small shields. On the cephalothorax there are also two pairs of antennae, an oral apparatus and five pairs of walking legs. Each of them performs certain functions. For example, the first pair ends with powerful claws that serve to grab food, tear it into pieces and protect it from enemies.
Six pairs of limbs are attached to the abdomen. The last pair of legs is expanded and together with the anal plate forms the caudal fin. In appearance, it resembles a fan. With the help of the anal fin, crayfish swim quickly enough with the rear end forward. Together they have 19 limbs.
Integument
The structural features of crayfish are primarily determined by its cover. As with all arthropods, it is represented by a cuticle, which forms a powerful external skeleton. Calcium carbonate, with which it is impregnated, gives it additional hardness.
Since the cuticle is not capable of stretching, the growth of crayfish is accompanied by periodic molting. This period is critical in the lives of these aquatic creatures. A few days before, the crayfish become restless, stop eating, and spend all their time in search of refuge. With the help of intensive movements of the body and limbs, they get rid of the old cover, from which they crawl out through a gap at the border of the cephalothorax and abdomen. In their reliable shelter, the cancers remain for up to ten days, until the new cuticle hardens.
Internal structure of crayfish
During embryonic development in all arthropods, a secondary body cavity is laid. But it does not persist throughout the life of the animal. In the process of individual development, this structure is destroyed, merging with the remnants of the primary and forming a mixed cavity. The gaps between the organs are filled in crustaceans with a fatty body. This is a type of loose connective tissue that performs important functions: storing nutrients, the formation of blood cells, and protection against mechanical damage.
Musculoskeletal system
The structure of crayfish is significantly different from the structure of mollusks and intestinal. In particular, they do not have a skin-muscle bag. Under the strong external skeleton are bundles of striated muscles that can contract quickly.
Major organ systems
The internal structure of river cancer is represented by rather complex organ systems. Digestive - end-to-end, with the presence of the liver and salivary glands, which secrete enzymes that break down nutrients. The final metabolic products are removed from the body using the excretory system represented by the malpigian vessels.
Respiratory organs of crayfish are caused by its aquatic environment, these are gills. The circulatory system is closely related to them. She is open. Blood vessels open into the body cavity, mix with its fluid, forming a hemolymph. It carries out the transportation of oxygen, carbon dioxide, nutrients, metabolic products.
The most important function of hemolymph is protective. It contains specialized cells, which carry out amoeboid movements, capture pathogens with pseudopods and digest them. The movement of hemolymph through the body provides a pulsating thickened vessel - the heart. Since blood mixes with the abdominal fluid and is not divided into arterial and venous, crayfish is a cold-blooded animal. This means that his body temperature decreases with 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, and the female has an ovary and paired oviducts. After fertilization, the eggs are on the abdominal legs of the female. So she shows maternal instinct, taking care of future offspring. In late spring or early summer, young crustaceans come out of them, which are an exact copy of adult individuals.
The nervous system is also quite complicated. It consists of differentiated departments: front, middle and back. The first regulates the work of the eyes, provides complex behavioral reactions of these animals, the rest innervate the antennae. The brain is anatomically connected to the abdominal nerve chain, from which separate nerve fibers leave the body.
Significance in nature and human life
Young individuals of crayfish form plankton of fresh water bodies - an important link in the food chain. Using the food of dead animals, they clean the habitat. Recently, due to the negative influence of humans, the number of populations of crayfish has declined sharply. In dirty water, the offspring of crayfish inevitably awaits death. This is also due to the important commercial importance of this arthropod representative. After all, the meat of crayfish is a valuable food product, and in some regions even a delicacy. It is rich in proteins, vitamins and minerals. Crayfish is the largest member of the class that lives in fresh water. To preserve this species in nature, until mid-summer, their fishing is officially prohibited.
The structure of crayfish is largely determined by its environment and determines its importance in nature and human life.