An arachnid is a type of joint-legged invertebrate animal that belongs to the class Arachnida. This class includes creatures such as spiders, scorpions, ticks, and mites. Arachnids typically have eight legs, a two-part body structure consisting of the cephalothorax and abdomen, and lack antennae. Arachnids are primarily terrestrial and can be found in various habitats around the world. They play essential roles in ecosystems, often acting as predators that help control insect populations. Some arachnids, like spiders, produce silk, which they use for building webs or capturing prey.