The world of fauna is many-sided and diverse. All life on Earth is divided into types. One of them is the arthropod type. It has about 2 million species and is represented by three classes: arachnids, insects and crustaceans.
Structure
All arthropods, regardless of class, have similarities. So, they have a symmetrical body, which is divided into several departments - segments. Most often there are three of them. The abdomen, head and chest are isolated from them. Sometimes the last two segments merge. They form the cephalothorax. The body of the arthropod is covered in hypodermis and chitinous cuticles, which are a kind of
outer skeleton. There are also several pairs of legs that extend from the segments to the sides. The type of arthropods differs from other invertebrates in that the legs of its representatives consist of several parts, between which resilin (elastic protein) is contained. Thanks to him, the creature can jump.
Circulatory system
The body cavity of animals representing the type of arthropods is myxocel. It is formed due to the connection of coelomic sacs with a blastocele. The fluid in the body cavity is called hemolymph. It mixes with blood and circulates in organs, between them, as well as in poorly developed vessels. As for the circulatory system, it is not closed. Arthropods have a heart. It is represented by a cerebrospinal blood vessel, which has acquired a certain shape. Through the lateral openings, the so-called ostia, which have valves, hemolymph enters the heart.
Digestive system
The arthropod digestive system is represented by the posterior, anterior and middle sections. The special tube is divided into sectors. Among them are the pharynx, stomach, esophagus. In addition, there is a hepatic outgrowth, due to which the release of enzymes occurs. The oral apparatus of arthropods is very complex.
Respiratory system
Depending on where the creature of the arthropod type lives, its respiratory system may take the form of lungs, gills, and trachea. But they are in their infancy. Pulmonary sacs (lungs) in this case are outgrowths of the body wall having a leaf-shaped shape and directed inward to the body cavity. They connect to the respiratory gap. Tracheas are formed by numerous branching tubes, which inside have chitin rings. Gas exchange in such animals occurs due to hemolymph, which delivers oxygen to all tissues.
Nervous system
The central nervous system of arthropods is formed by the brain and nerve chain. It is located in the peritoneum. The chain has a connection of nerve nodes in the abdominal, head and thoracic regions, due to which animals of this type have well-developed sensory organs.
Other systems
As for the excretory system, it is represented by malpigian vessels and methanephridia. Animals such as arthropods are heterosexual, with strongly pronounced dimorphism. The muscular system is also present in these animals and is represented by striated tissue.