Arthropods are the most common animal species on the planet. Just imagine: their number is ten times greater than the number of all other species combined! The general characteristics of arthropods, the features of their external and internal structure, and vital processes are presented in our article.
Habitat
Arthropods are unique animals. They have mastered absolutely all habitats. They can be found in various land areas, in fresh and salty 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 related to 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. Limbs are located on them, the number of which is an important systematic sign.
On the head are antennae, which are organs of touch, and eyes. The chest carries paired articulated limbs and outgrowths of the integument - wings. This feature of the structure determines their ability to fly. The abdomen is most often deprived of limbs, or they are largely modified. For example, in spiders, they are modified into specialized warts.
Integument
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 solid and powerful outer skeleton, additionally saturated with calcium carbonate. Since chitin is not capable of stretching like skin collagen, the growth and development of arthropod animals is accompanied by periodic molting.
Body cavity
Arthropods are animals in which a secondary body cavity is laid during ontogenesis, even at the stage of embryonic development. 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 the presence of a fatty body - a type of connective tissue that fills the gaps between the organs. Its additional functions are the supply of nutrients, the formation of blood cells, and protection against mechanical damage.
Musculature
The arthropod muscular system is formed from striated tissue. Its fibers are bundled. This structure determines the exact and instant movements of arthropods.
Organ systems
The digestive system of these animals is cross-cutting. Fast metabolism helps salivary gland and liver enzymes. Arthropods are organisms that are diverse in their types of nutrition. 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 a heart and a system of blood vessels that open into the body cavity. There, the blood mixes with the abdominal fluid, forming a special substance - hemolymph, which carries out gas exchange.
Respiratory organs are determined by the habitat. For aquatic organisms, these are gills. in terrestrial - trachea or pulmonary sacs.
The nervous system is quite complicated. The brain is represented by specialized departments: front, middle and rear. Each of them innervates certain organs. Arthropods are characterized by instinctive behavior. And besides congenital reflexes, acquired ones are also formed - conditioned ones.
The reproductive system is most often dioecious. But fertilization can be both internal and external, which occurs outside the body of the female. Like development - direct and indirect - with the larval stage.
Classes such as Arthropods
Talk about further separation. Several systematic units are united by the type of arthropods: a class of crustaceans, arachnids, and insects.
Each of them has its own characteristic features. 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 in humid land. Class Arachnids are easy to distinguish by their appearance. Their body consists of the cephalothorax and abdomen. They have four walking legs, tentacles and chelicerae - 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 parasitic ones, has special outgrowths of covers - wings.
Thus, representatives of the type of arthropods have progressive structural features that allow them to adapt to different living conditions and occupy their niche of living.