The present article represents the first part of a review of fossil heterostigmatic mites collected from late Eocene Rovno amber. Here, mites of the families Tarsocheylidae, Dolichocybidae, and Acarophenacidae are described, with Tarsocheylidae and Dolichocybidae recorded for the first time from amber. A new genus and four new species are described, namely, Hoplocheylus similis sp. nov. (Tarsocheylidae), Dolichocybe elongata sp. nov. (Dolichocybidae), Proadactylidium fossibilis gen. and sp. nov. and Paradactylidium sineunguis sp. nov. (Acarophenacidae). The extant species Acarophenax lacunatus Cross and Krantz, 1964 and A. assanovi Livshitz and Mitrofanov, 1974 are transferred to the new genus Proadactylidium. A revised key to the genera of Acarophenacidae is presented. The homologies of prodorsal setae in Acarophenacidae are reconsidered and reviewed.

Two new species of myrmecophilous pygmephoroid mites, Petalomium hofstetteri n. sp. (Neopygmephoridae) and Caesarodispus klepzigi n. sp. (Microdispidae), associated with the red imported fire ant (Solenopsis invicta Buren) (Hymenoptera: Formicidae) are described from Louisiana, U.S.A.

A new genus Pseudoeupodes Khaustov, gen. n. and new species Pseudoeupodes porosus sp. n. are described from moss in Crimea. The taxonomy of the Eupodidae and some other families and genera of Eupodoidea is reviewed. The genus Turanopenthalodes Barilo, 1988 is transferred from Penthalodidae to Penthaleidae. The family Cocceupodidae Jesionowska, 2010 and the genus Filieupodes Jesionowska, 2010 are considered as junior synonyms of Eupodidae Koch, 1842 and Cocceupodes Thor, 1934, respectively. A key to genera of the family Eupodidae is provided.

Five species of myrmecophilous microdispid mites (Acari: Microdispidae) are recorded from Western Siberia, Russia. Unguidispus lasii Kurosa, 1979, U. japonicus Kurosa, 1979, Caesarodispus minutus (Sevastianov, 1981), and C. samsinaki (Mahunka, 1967), comb. n. are reported from Russia for the first time. Unguidispus polyctenus (Sevastianov, 1969) and Caesarodispus samsinaki are redescribed. The keys to species of the genera Unguidispus Mahunka, 1970 and Caesarodispus Mahunka, 1977 are provided.

The female of a new fossil genus and species, Rhombometridium pankowskiorum gen. and sp. nov. (Acari: Trochometridiidae), is described from Cretaceous Kachin amber. The new genus is characterized by the presence of well-developed sporothecae anteriad legs III, each sporotheca containing several ovoid fungal spores. This is the oldest (ca. 100 Mya), evidence of symbiosis between mites and fungi and the first fossil record of the mite family Trochometridiidae. The new genus shares synapomorphies with the family Trochometridiidae (presence of sporothecae between bases of legs III and IV) and Caraboacaridae (rhombic body shape, absence of setae v2, absence of palpal solenidion, palps fused with distinctly widened gnathosomal capsule), and potentially represents a transitional form or a missing link between these two closely related families. We also compare the sporothecae of R. pankowskiorum with those of other heterostigmatic mites.

The first fossil mite of the family Pyemotidae (Acari: Heterostigmata) is recorded. Pyemotes primussp. nov. is described from the Late Eocene of the Rovno amber from a syninclusion with the bark...