Walter, David Evans Department of Invertebrate Zoology, Royal Alberta Museum, Edmonton, Alberta, Canada.
Last reviewed:October 2019
- Body plan
- Development, reproduction, and genetics
- Ecology and distribution
- Related Primary Literature
- Additional Reading
A taxon of arachnids (traditionally considered a subclass of the Arachnida), comprising the mites and ticks. The Acari (also Acarina) consist of two superorders of small to minute arachnids. They have two body regions (Fig. 1)—a headlike gnathosoma (“jaw body”) or capitulum (“little head”) and a sacklike idiosoma (“special body”)— and a hexapod (six-legged) larval stage (Fig. 2b). The smallest known mite is about 0.08 mm (0.003 in.) in length as an adult, whereas the largest, a tick fully engorged with blood, is about 30 mm (1.2 in.). More than 50,000 species have been described, including many that have importance in a number of areas: medical [ticks, scabies, house dust mites, and chiggers (Fig. 2b)], veterinary (mange mites and rodent mites), agricultural (spider mites, poultry mites, and stored-product mites), and ecological [oribatid mites (Fig. 2a), mesostigmatid mites (Fig. 1), and water mites]. Perhaps as many as 1 million species are alive today. Current research indicates that the two superorders (Acariformes and Parasitiformes) may be only distantly related; that is, mites consist of two distinct and separate groups of arachnids. See also: Arachnida
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