Arthropoda

Arachnids are a class of joint-legged invertebrate animals in the subphylum Chelicerata. All arachnids have eight legs, although the front pair of legs in some species has converted to a sensory function, while in other species, different appendages can grow large enough to take on the appearance of extra pairs of legs.

An arthropod is an invertebrate animal having an exoskeleton, a segmented body, and jointed appendages. Arthropods are members of the phylum Arthropoda, and include the insects, arachnids, and crustaceans.