Philip, Cornelius B. Department of Entomology, California Academy of Sciences, San Francisco, California.
Last reviewed:May 2021
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An arachnid taxon comprising the ticks. Ticks are arachnids (Fig. 1). Specifically, they are members of the Ixodida, which is considered to be an order or suborder (depending on the exact classification) of the subclass Acari (Acarina) in the class Arachnida. Ticks differ from mites, their nearest relatives, in their larger size and in having a pair of breathing pores, or spiracles, behind the third or fourth pair of legs. Ticks have a gnathosoma (or so-called head or capitulum), which consists of a base (basis capituli), a pair of palps, and a rigid, elongated, ventrally toothed hypostome that anchors the parasite to its host. They also have a pair of protrusible cutting organs, or chelicerae, which permit the insertion of the hypostome. The stages in the life cycle are egg, larva, nymph, and adult. Larvae have three pairs of legs; nymphs and adults have four pairs. The approximately 900 known species are all bloodsucking, external parasites of vertebrates, including amphibians, reptiles, birds, and mammals. See also: Acari; Arachnida; Metamorphosis; Parasitology
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