Synonyms and other taxonomic changes
~50,000 described spp. worldwide (many times as many undescribed)
Six-legged condition: Acarine larvae normally have 6 legs rather than 8, unless that feature has been lost secondarily. Some mites may have no legs at all at some life stages. This condition doesn't follow a particular taxonomic pattern, but is based more on species or life-stage ecology. Parasitic or phoretic mites, in particular, may lack some or even all legs. Some adult mites have 6 legs (one pair lost secondarily), e.g., in Metacheyletia spp. the hind legs are reduced or absent. (Jon Oliver's comments)
Many have complex symbiotic associations with the larger organisms on which they live.
Some are serious pests.
It may not be a monophyletic group.