What is "mesostigmata"

Mesostigmata is an order of mites belonging to the Parasitiformes. Unlike most members of that group, many of these mites are not parasitic but free-living and predatory. They can be recognized by the single pair of spiracles positioned laterally on the body.

The family with the most described species is Phytoseiidae. Other families of note are Diplogyniidae, Macrochelidae, Pachylaelapidae, Uropodidae and Veigaiidae.