The world of fauna is many-sided and diverse. All living things on Earth are divided into types. One of them is the phylum Arthropoda. It has about 2 million species and is represented by three classes: arachnids, insects and crustaceans.
Building
All arthropods, regardless of class, are similar to each other. So, they have a symmetrical body, which is divided into several sections - segments. Most often there are three. Of these, the abdomen, head and chest are distinguished. Sometimes the last two segments merge. They form the head. The body of arthropods is covered with hypodermis and chitinous cuticle, which are something like an external skeleton. There are also several pairs of legs that extend from the segments to the sides. The type of arthropod differs from other invertebrates in that the legs of its representatives consist of several parts, between which resilin (an elastic protein) is contained. Thanks to him, the creature can jump.
Circulatory system
The body cavity of animals representing the type of arthropods is a mixocoel. It is formed due toconnection of the coelomic sacs with the blastocoel. The fluid in the body cavity is called hemolymph. It mixes with the blood and circulates in the 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 spinal blood vessel, which has acquired a certain shape. Through the side openings, the so-called ostia, which have valves, the hemolymph enters the heart.
Digestive system
The digestive system of arthropods is represented by the posterior, anterior and middle sections. The special tube is subdivided into sectors. Among them are the pharynx, stomach, esophagus. In addition, there is a hepatic outgrowth, due to which enzymes are secreted. The mouthparts of arthropods are very complex.
Respiratory system
Depending on where an arthropod lives, its respiratory system may look like lungs, gills, and windpipes. But they are in their infancy. Pulmonary sacs (lungs) in this case are outgrowths of the body wall, having a leaf-like shape and directed inside the body cavity. They connect with the respiratory gap. The tracheae are formed by numerous branching tubules, which have chitinous rings inside. Gas exchange in such animals occurs due to the hemolymph, which delivers oxygen to all tissues.
Nervous system
CentralThe nervous system of arthropods is formed by the brain and the 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 sense organs.
Other systems
As for the excretory system, it is represented by malpighian vessels and metanephridia. Animals of the arthropod type are heterosexual, and with strongly pronounced dimorphism. The muscular system is also present in these animals and is represented by striated tissue.
