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
Parasitic flies of domestic animals transmitted organisms to develop, multiply and be exposed to further vertebrate hosts where they can complete their life cycle. Only the adult flies are involved in this biological transmission, in contrast to biological transmission by other arthropods such as lice or ticks in which all active stages of the life-cycle feed on blood. Typical genera are "Culex", "Aedes", and "Anopheles". The basic structure of dipteran flies is illustrated in the diagram. Veterinary parasitology also covers arthropods in the Class Acari, the ticks of domestic animals and mites of livestock which have distinctly different structure from arthropods in the Class Insecta.