The internal anatomy of the scale mite Pterygosoma pseudotrapelus (Trombidiformes, Pterygosomatidae)

Abstract

This study is the first description of the internal anatomy of the scale mites using the example of parasitizing Pterygosoma pseudotrapelus (Bochkov et al., 2009) – a parasite of agamid lizards. Data on histology of the integument, digestive tract, excretory organs, prosomal glands, tracheae, and body-cavity tissues of females, supplemented by the ultrastructure of major organs, are discussed in comparison with information from other groups of the Acari. The female reproductive system was examined only at the light microscopic level. The shape of mite body is adapted to the existence under the scales of the reptile, where the parasite spends its entire life. The width of the adult females is nearly twice their length, resulting in the eccentric position of certain internal organs: the large reproductive system is oriented across the body, so that the ovary with developing oocytes occupies the right side of the idiosoma, while oviduct, seminal receptacle, and vagina are displaced to the left. The structure of the tracheal system and the podocephalic complex of P. pseudotrapelus is similar to that of Tetranychoidea, a group also regarded as one of the lower taxa in the cohort Raphignathina. A number of previously unknown primitive traits identified in the study confirm a relatively basal position of the scale mites within Raphignathina. These include a panoistic ovary, the postcolon instead of an excretory organ of more advanced forms, and 2 pairs of podocephalic acinar glands against the general trend of their reduction in this cohort. An unpaired tracheal gland was found independent from the podocephalic system. The coxal glands lack a filtering sacculus and their epithelium forms mutual interdigitations with the surrounding modified ventricular wall.