Acari

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.

Most acarines are minute to small (e.g., 0.08–1.00 millimetre or 0.003–0.039 inches), but the largest Acari (some ticks and red velvet mites) may reach lengths of 10–20 millimetres (0.4–0.8 in). Over 50,000 species have been described (as of 1999) and it is estimated that a million or more species may exist.