The Acari or Acarina is the taxonomic group that includes ticks and mites. This group is the most diverse and abundant of the arachnids, and its fossil history goes back to the Devonian era. There are three major lineages, the Opilioacariformes, Acariformes and Parasitiformes, with more than 45,000 known species worldwide. The Acariformes are the most diverse of the three orders of mites. There are over 32,000 described species in 351 families. Many species of Parasitiformes, including the ticks, are parasitic, but not all; for example, about half of the 10,000 known species in the suborder Mesostigmata are predatory and cryptozoan, living in the soil-litter, rotting wood, dung, carrion, nests or house dust.