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Freebase Commons Metaweb System Types /type

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Freebase Commons Common /common

  • Acari are a taxon of arachnids that contains mites and ticks. The diversity of the Acari is extraordinary and its fossil history goes back to at least the early Devonian period. As a result, acarologists have proposed a complex set of taxonomic ranks to classify mites. In most modern treatments, the Acari is considered a subclass of Arachnida and is composed of two or three superorders or orders: Acariformes, Parasitiformes, and Opilioacariformes; the latter is often considered a subgroup within the Parasitiformes. The monophyly of the Acari is open to debate, and the relationships of the acarines to other arachnids is not at all clear. In older treatments, the subgroups of the Acarina were placed at order rank, but as their own subdivisions have become better-understood, it is more usual to treat them at superorder rank. Most acarines are minute to small, but the largest Acari may reach lengths of 10–20 millimetres. Over 50,000 species have been described and it is estimated that a million or more species may exist.

Freebase Commons Biology /biology

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