Arachnid Arachnid Arachnids () are a class (Arachnida) of joint-legged invertebrate animals (arthropods), in the subphylum Chelicerata. Almost all adult 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. The term is derived from the Greek word ("aráchnē"), from the myth of the hubristic human weaver Arachne who was turned into a spider. Spiders are the largest order in the class, which also includes scorpions, ticks, mites, harvestmen, and solifuges. Almost
Bird feet and legs The legs are attached to a strong assembly consisting of the pelvic girdle extensively fused with the uniform spinal bone (also specific to birds) called the "synsacrum", built from some of the fused bones. Birds are generally digitigrade animals (toe-walkers), which affects the structure of their leg skeleton. They use only their hindlimbs to walk (bipedalism). Their forelimbs evolved to become wings. Most bones of the avian foot (excluding toes) are fused together or with other bones, having changed their function over time. Some lower bones of the foot are fused to form the tarsometatarsus – a third segment of