| abstract | A new genus, Dytiscacarus gen nov. Hajiqanbar and Lindquist, based on three new species and representing a new family of trombidiform mites, is described from Iran and the USA. These mites are highly specialized parasites of beetles in the family Dytiscidae, undergoing their entire life cycle while inhabiting the space beneath the elytra of their hosts. The new taxon is autapomorphic in three aspects, characteristic of all active instars: a pair of gnathosomatic neostigmata on the dorsal face of the infracapitulum, the morphological arrangement of the deeply retractable cheliceral stylets, and the pretarsi of all legs lacking an empodium and bearing paired claws strongly modified into sclerotized tenent-like structures. This lineage is unique among parasitic mites in there being no previous records of aquatic beetles harbouring all instars of a highly specialized mite. The age of this mite–insect association may go back to nearly 110–90 Mya. Placement of the new taxon in the cohort (or hyporder) Raphignathina is discussed. Invertebrate parasitism in the supercohort (or infraorder) Eleutherengonides, aquatic beetles harbouring the new taxon of parasitic mites, and the dispersal and host transfer of these mites are reviewed and discussed. |