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! General characteristics of arthropods, features of their external and internal structure, life processes 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 s alt water bodies, soil, and parasitic species live in other organisms. They are able to crawl, make moves in the soil, swim, and most importantly, fly.
Features of the external structure
The name of this type of chordates is connected with their morphology. Arthropods are animals that have a segmented body and limbs. Agree, spiders, crayfish and bees are quite outwardly different from each other. But,despite this, their body consists of three parts: head, chest and abdomen. They have limbs, the number of which is an important systematic feature.
On the head are antennae, which are organs of touch, and eyes. The chest bears paired jointed limbs and outgrowths of the integument - wings. This feature of the structure 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.
Sheaths
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 external skeleton, additionally impregnated with calcium carbonate. Since chitin is not capable of stretching like skin collagen, the growth and development of arthropods is accompanied by periodic molting.
Body cavity
Arthropods are animals in which during ontogenesis, at the stage of embryonic development, a secondary body cavity is laid. But over time, its lining is gradually destroyed, and it merges with the primary one. Therefore, the body cavity of arthropods is mixed. A characteristic feature is also the presence of a fat body - a type of connective tissue that fills the gaps between organs. Its additional functions are the supply of nutrients, the formation of blood cells, protection from mechanical damage.
Muscles
Muscular systemarthropod is formed from striated tissue. Its fibers are collected in bundles. This structure determines the precise and instantaneous movements of arthropods.
Organ systems
The digestive system of these animals is of a through type. Fast metabolism helps to carry out the enzymes of the salivary gland and liver. Arthropods are organisms that are diverse in terms of food types. Among them there are saprotrophs, and predators, and parasites, and blood-sucking species.
The excretory system is most often represented by specialized tubules or malpighian vessels. Circulatory - open type. It consists of the heart and a system of blood vessels that open into the body cavity. There, the blood mixes with the cavity fluid, forming a special substance - hemolymph, which carries out gas exchange.
Respiratory organs are conditioned by the environment. For aquatic organisms, these are gills. in terrestrial - trachea or lung sacs.
The nervous system is quite complicated. The brain is represented by specialized sections: anterior, middle and posterior. Each of them innervates certain organs. Arthropods are characterized by instinctive behavior. And besides congenital reflexes, acquired ones are also formed - conditional.
The reproductive system is most often of a dioecious type. But fertilization can be both internal and external, which occurs outside the body of the female. Like development - direct and indirect - with a stagelarvae.
Classes of type Arthropods
Let's talk about further separation. Several systematic units are united by the type Arthropods: the class crustaceans, arachnids and insects.
Each of them has its own characteristics. After all, it is not in vain that the most numerous on the planet is precisely the type of arthropods. The crustacean class differs from others in the presence of two pairs of antennae on the head, gills and green glands. They are aquatic inhabitants, although some of them are able to live on wet land areas. Class Arachnids are easy to distinguish by external signs. Their body consists of a cephalothorax and an abdomen. They have four walking legs, tentacles and chelicerae - special sharp limbs with which spiders pierce the body of their prey. A characteristic feature of insects is the presence of three pairs of limbs on the chest. The predominant number of species, in addition to parasitic ones, has special outgrowths of integuments - wings.
Thus, representatives of the arthropod type have progressive structural features that allow them to adapt to various living conditions and occupy their habitat niche.
