Arachnid and that there may be up to 600,000 in total. 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,
Ticks of domestic animals animal hosts, but their feeding mechanisms are distinctive. All ticks have an incomplete metamorphosis: after hatching from the egg, a series of similar stages (= instars) develops from a six-legged larva, to eight-legged nymph, and then a sexually developed, eight-legged adult. Between each stage is a molt (ecdysis) which enables the developing tick to expand within a new external skeleton. Ticks are grouped in three families of which two have genera of importance to domestic animals, as follows. The family Argasidae contains the important genera "Argas", "Ornithodoros", and "Otobius". These genera are known as soft ticks because their outer body