The main characteristic of representatives of this group of animals is the presence of a chitinous exoskeleton.

Arthropods are distributed almost worldwide and play a significant role everywhere. Insects, along with mammals and birds, are the dominant group of terrestrial animals. There are at least 1.5 million species of insects, possibly much more. It is estimated that their number ranges from 3–10 to 30 million. Although arachnids and myriapods have not reached the same diversity as insects, they are also widely spread. Finally, crustaceans inhabit almost all latitudes and depths of the world’s oceans. In some regions, small crustaceans are the dominant group of plankton.

The body of arthropods is segmented and divided into the head, thorax, and abdomen. It is fully or partially covered with chitin. They grow only during molting. Their limbs are jointed and serve functions such as movement, respiration, protection, grasping, etc. In some arthropods, the head and thorax are fused into a cephalothorax. The digestive system is differentiated. The mouthparts are formed from modified appendages. Respiration is gill-based (in crustaceans), pulmonary, or tracheal (in arachnids and insects). The circulatory system is open. The nervous system consists of the brain and a ventral nerve cord. Many arthropods have well-developed sensory organs. Excretory organs include metanephridia and Malpighian tubules. Most arthropods are dioecious, and cases of hermaphroditism are rare. Development occurs with complete or incomplete metamorphosis. In incomplete metamorphosis, insects do not have a pupal stage.

The role of arthropods in nature is very significant. They inhabit almost all environments and influence them. Arthropods serve as food for animals, pollinate plants, transmit infectious diseases, and damage agricultural crops. Some species, such as bees and the silkworm, are considered domesticated animals.