[A review of the external morphology of the family pterygosomatidae and its systematic position within the Prostigmata (Acari: Acariformes)].

According to the traditional views mites of the family Pterygosomatidae belong to the cohort Anystina (Krantz, 1978; Kethley, 1982). Kethley (1982), however, noted similarities between these mites and representatives of the cohort Eleutherengona. In the tree diagram suggesting relationships among higher taxa Prostigmata proposed by Kethley (in Norton et al., 1993) this family derives from the eleutherengone clade. However, the characters and ranges of taxa upon which Kethley's hypothesis was based were not stated. In this paper, the external morphology of pterygosomatid mites is analyzed. The data provide strong evidence supporting a close relationship between Pterygosomatidae and the <<higher>> eleutherengone mites (Raphignathae and Heterostigmata). The setation of Pterygosomatidae is similar that of Raphignathae by the absence of trichobothria, adanal setae, and by the strongly reduced leg setation. In these mites, as in the <<higher>> eleutherengones (Raphignathae) an aedeagus is present, in females, the genital and anal openings are situated close to each other and are covered by a pair of common folds, in males these openings are fused, the leg femora are not separated onto basi- and telofemur, the naso, sejugal furrow, genital papillae, and the larval Claparede's organs are absent. Some similarities in the structure of the gnathosoma and the chelicerae with Anystina (including Parasitengona) are, probably, symplesiomorphies or convergently developed. Moreover, in pterygosomatids, the gnathosomal setation is represented by a single pair of gnathobasal setae, and the cheliceral and adoral setae, present in anystoid mites and early derivative eleutherengones, are absent. We believe, therefore, that Pterygosomatidae is a separate branch within the cohort Eleutherengona. Its exact position is, however, still unclear. Among pterygosomatid genera, mites of the genus Pimeliaphilus, which possess the maximal setation, are closest to the <<freelivings>> habitus. These mites are known from different parts of the world parasitizing mostly secretively living arthropods. We suggest that ancestors of the family were initially associated with arthropods and parasitism of pterygosomatids on lizards is the result of host switching from arthropods to these hosts.