The scorpions are primitive, ancient chelicerates that have changed little since the Silurian. The body consists of a cephalothorax of six segments and an abdomen of twelve. The cephalothorax is covered by a carapace and bears chelicerae, pedipalps, and four pairs of walking legs. Scorpions are nocturnal predators feeding primarily on insects and other arthropods.
Digestion begins externally and is completed intracellularly.
The nervous system is annelid-like with some cephalization and the heart is a dorsal tube in the anterior abdomen. The blood vascular system includes a hemocoel and the coelom is reduced. Excretion is accomplished by coxal glands and Malpighian tubules. Respiration is via book lungs and the respiratory pigment hemocyanin is present in solution in the blood. There is a variety of sense organs.