What are arachnids primarily characterized by?

Arachnids are primarily characterized by having a jointed body that is divided into two main regions: the cephalothorax and the abdomen. Additionally, they possess four pairs of legs, totaling eight legs. This distinct body structure differentiates them from insects, which have three pairs of legs and a body divided into three parts. The two-part body structure of arachnids allows for various adaptations that have contributed to their success in diverse habitats, such as terrestrial environments. The presence of eight legs is a key feature that classifies them within the class Arachnida, which includes spiders, scorpions, ticks, and mites.