This document defines and describes key anatomical terms used to classify groups of arthropods. It discusses the cephalothorax, thorax, and abdomen found in crustaceans, as well as specific structures like the carapace, mandibles, chelipeds, swimmerets, chelicerae, pedipalps, and spinnerets. It concludes with three key concepts: arthropods are classified by body segments and appendages, especially mouthparts; crustaceans typically have two antennae, two or three body sections, and mandibles; and chelicerates have chelicerae mouthparts and two body sections, with nearly all having four pairs of walking legs.