Systematics and Taxonomy
The Prostigmata make up the bulk of the acariform clade Trombidiformes, which also contains the minor and quite ancient lineage Sphaerolichida. The trombidiform mites are possibly the most promoising approach to untangle the systematics, taxonomy and phylogeny of the notoriously complex Acariformes. Trombidiformes and the other acariform clade, Sarcoptiformes, were formerly considered suborders but this does not allow for a sufficiently precise classification of the mites and is adjusted in more modern treatments.
They contain a few of the little-known "Endeostigmata" – apparently an assemblage of several specialized but unrelated lineages – which for the most part appear to be Sarcoptiformes however. In addition, the Trombidiformes include the bulk of the presumed group of mites called "Actinedida". This taxon is still commonly encountered in systematic treatments. However, modern cladistic studies time and again fail to find any monophyletic group corresponding to the "Actinedida". Thus, they appear to be an evolutionary grade rather than an evolutionary lineage, united not by their apomorphies but by the lack of such characters that have evolved after the Acariformes separated from the Parasitiformes. Thus, the "Actinedida" seem to be a massively paraphyletic "wastebin taxon", uniting all Acariformes that are not "typical" Oribatida and Astigmata.
The Prostigmata present their own taxonomic and systematic problems even in the redefined monophyletic delimitation. They are variously subdivided into the Anystina and Eleutherengona, and Eupodina. The delimitation and interrelationships of these groups are entirely unclear; while most analyses find one of the latter two but not the other to be a subgroup of the Anystina, neither of these mutually contradicting hypotheses is very robust; possibly this is a simple error because phylogenetic software usually fails in handling non-dichotomous phylogenies. Consequently it may be best for the time being to consider each of the three main prostigmatan lineages to be equally distinct from the other two, not including either Eleutherengona or Eupodina in the Anystina in accord with the traditional view – the suborder Anystina are here considered the largest possible clade containing the Anystidae but no taxon assigned to the other two suborders.
Read more about this topic: Prostigmata