General characteristics, features, structure of arthropods. Type of arthropods, a class of crustaceans. Arthropods are ...

Arthropods are the most common representatives of the animal world on the planet. Just imagine: their number is ten times greater than the number of all other species combined! The general characteristics of arthropods, peculiarities of their external and internal structure, processes of vital activity are presented in our article.

Habitat

Arthropods are unique animals. They have mastered absolutely all habitats. They can be found on various parts of the land, in fresh and salt water bodies, soil, and parasitic species also live in other organisms. They are able to crawl, make moves in the soil, swim, and most importantly - fly.

Features of external structure

The name of this type of chordates is related to their morphology. Arthropods are animals that have a segmented body and limbs. Agree, spiders, crayfish and bees are quite different from each other. But, despite this, their body consists of three parts: the head, chest and abdomen. They have limbs, the number of which is an important systematic feature.

On the head are the antennae, which are the organs of touch, and the eyes. The breast bears paired, articulate limbs and the outgrowths of the veins are the wings. This feature of the structure and determines their ability to fly. The abdomen is most often devoid of limbs, or they are largely modified. For example, in spiders they are modified into specialized warts.

Covers

The body of all arthropods is covered with a dense cuticle consisting of a special substance - chitin. In some species, such as crayfish and crabs, the cover forms a hard and powerful outer skeleton, additionally impregnated with calcium carbonate. Since chitin is not capable of stretching like skin collagen, the growth and development of arthropod animals are accompanied by periodic moults.

Body cavity

Arthropods are animals that have a secondary body cavity at the stage of embryonic development during ontogenesis. But over time, its lining is gradually destroyed, and it merges with the primary. Therefore, the body cavity of arthropods is mixed. A characteristic feature is also the presence of the fat body - a kind of connective tissue that fills the spaces between the organs. Its additional functions are the supply of nutrients, the formation of blood cells, protection against mechanical damage.

Musculature

The muscular system of arthropods is formed from striated tissue. Its fibers are gathered in bundles. This structure determines the precise and instantaneous movements of arthropods.

Systems of organs

The digestive system of these animals is through type. A rapid metabolism helps to carry out the enzymes of the salivary gland and liver. Arthropods are organisms that are diverse in their types of nutrition. Among them are found saprotrophs, and predators, and parasites, and bloodsucking species.

The excretory system is most often represented by specialized ducts or malpighian vessels. The circulatory is of non-closed type. It consists of a heart and a system of vessels that open into the body cavity. There, the blood is mixed with the cavity fluid, forming a special substance - hemolymph, which carries out gas exchange.

The respiratory organs are caused by the habitat. For aquatic organisms, these are the gills. In the ground - trachea or pulmonary sacs.

The nervous system is rather complicated. The brain is represented by specialized departments: front, middle and posterior. Each of them innervates certain organs. Arthropods are characterized by instinctive behavior. And besides the congenital reflexes, the acquired ones are formed - conditional ones.

The sexual system is most often of the dioecious type. But fertilization can be both internal and external, which occurs outside the body of the female. Like development - direct and indirect - with the stage of the larva.

Classes of the Arthropoda type

Let's talk about further separation. Several systematic units combine the type Arthropoda: a class of crustaceans, arachnids and insects.

Each of them has its own characteristics. It's not for nothing that the most numerous on the planet is the type of arthropods. The crustacean class differs from the others in the presence of two pairs of antennae on the head, gills and green glands. They are water inhabitants, although some of them are able to live on wet land. The class of the Arachnids can be easily distinguished by external features. Their body consists of the cephalothorax and abdomen. They have four walking legs, tentacles and chelicera - special sharp limbs with which spiders pierce the body of their victim. A characteristic feature of insects is the presence on the chest of three pairs of limbs. The predominant number of species, except for parasitic species, has special outgrowths - wings.

Thus, representatives of the arthropod type have progressive features of the structure that allow them to adapt to different living conditions and occupy their own niche.