The Acariformes are the more diverse of the two superorders of mites. Over 32,000 described species are found in 351 families, and an estimated total of 440,000 to 929,000 species occur, including undescribed species.
The Acariformes can be divided into two main clades - Sarcoptiformes and Trombidiformes. In addition, a paraphyletic group containing primitive forms, the Endeostigmata, was formerly also considered distinct. The latter is composed of only 10 families of little-studied, minute, soft-bodied mites that ingest solid food, such as fungi, algae, and soft-bodied invertebrates such as nematodes, rotifers, and tardigrades. These clades were formerly considered suborders, but this does not allow for a sufficiently precise classification of the mites and is abolished in more modern treatments; the Endeostigmata are variously considered to form a suborder on their own (the old view) or are included mainly in the Sarcoptiformes, thus making both groups monophyletic.