Two new genera and two new species of the mite family Neopygmephoridae (Acari: Heterostigmata) associated with small mammals from USA

Two new monotypic genera and two new species of the mite family Neopygmephoridae (Acari: Pygmephoroidea) associated with small mammals are described from USA: Crossdania gen. nov. with the type species Crossdania tubulosa sp. nov. associated with Northern grasshopper mouse, Onychomys leucogaster (Rodentia: Cricetidae) and Great Basin pocket mouse, Perognathus parvus (Rodentia: Heteromyidae), and Theriodania gen. nov. with the type species Theriodania venusta sp. nov. associated with Merriam's kangaroo rat, Dipodomys merriami (Rodentia: Heteromyidae).

Mites of the genus Pygmephorus are well studied in North America (Mahunka 1973(Mahunka , 1974(Mahunka , 1975Smiley 1978;Smiley andWhitaker 1979, 1984), while mites of the family Neopygmephoridae are poorly studied and only four species have been reported in association with small mammals: Bakerdania jonesi Mahunka, 1975, B. plurisetosa Mahunka, 1975, B. equisetosa Cross, 1970, and Kerdabania quadrata (Ewing, 1917) (Mahunka 1975). During the study of Neopygmephorid mites collected on small mammals by the junior author and associates, two new remarkable new genera were found and are described below.

Materials and methods
Mites were collected directly from small mammals by combing through the fur using dissecting needles with a dissecting microscope and mounted in Hoyer's medium. The terminology of the idiosoma and legs follows that of Lindquist (1986); the nomenclature of subcapitular setae and the designation of cheliceral setae follow those of Grandjean (1944Grandjean ( , 1947, respectively. The systematics of Pygmephoroidea follows that of Khaustov (2004Khaustov ( , 2008. All measurements are given in micrometers (μm) for the holotype and paratypes (in parentheses). For leg chaetotaxy, the number of solenidia is given in parentheses. Mite morphology was studied using a Carl Zeiss AxioImager A2 compound microscope with phase contrast and DIC objectives. Photomicrographs were taken with Hitachi KP-HD20A and AxioCam 506 color digital cameras.
Differential diagnosis -The new genus is most similar to Protobakerdania Khaustov and Minor, 2018 by the absence of a median genital sclerite, hook-like setae d of femur I, the same leg setation, and entire posterior margin of the posterior sternal plate. The new genus differs from Protobakerdania by the long and narrow empodia on tarsi II and III and very long empodium on tarsus IV (vs not elongate, flipper-like in Protobakerdania), by the characteristically modified setae l" of genu, d of tibia, pl", tc", and (pv) of tarsus of leg II (vs. not modified in Protobakerdania). From all known genera of Neopygmephoridae the new genus differs by the presence of sclerotized tube-like structures under tergite H (vs absent in all other genera) and by the absence of claws on tarsus IV (vs present in all other genera).
Species included -The genus Crossdania includes only one species, Crossdania tubulosa sp. nov.
Etymology -The generic name is a combination of two words: Cross, the family name of late American acarologist Earl Cross, and dania, the common ending of many Neopygmephorid genera. The new genus is named after Earl Cross for his contributions in the study of heterostigmatic mites.
Differential diagnosis -The new genus is most similar to Crossdania gen. nov. by the presence of modified setae on leg II and very long empodium on tarsus IV. The new genus differs from Crossdania gen. nov. by the presence of claws on tarsus IV (vs absent in Crossdania), by the fan-shaped seta d of femur I (vs. hook-like in Crossdania), by the absence of solenidion ω 2 (vs. present in Crossdania), and by unusual elongate 2-chambered stigmata (vs. round, 1-chambered in Crossdania).
Species included -The genus Theriadania includes only one species Theriadania venusta sp. nov.
Male and larva unknown. Type deposition -The holotype and 1 paratype are deposited in the United States National Museum, Washington, USA; other paratypes are deposited in the mite collection of the Tyumen State University Museum of Zoology, Tyumen, Russia.
Etymology -The name of the new species is derived from Latin venustus meaning beautiful, and refers to the presence of many modified setae on idiosoma and legs.

Discussion
Both newly described monotypic genera are characterized by a remarkable combination of characters. Crossdania tubulosa sp. nov. has unusual well sclerotized paired tubelike structures under tergite H (Fig.5C). Similar structures were not previously recorded in neopygmephorid and other heterostigmatic mites. These structures most likely represent part of insemination system, like spermathecae in astigmatid and mesostigmatid mites. However, these tube-like structures are located near the anal opening and could also be sclerotized ducts of glands. Another unusual character of C. tubulosa sp. nov. is the complete absence of claws on tarsus IV. The complete absence of claws on tarsus IV is unknown in all previously described neopygmephorid mites, however in some genera (for example Petalomium) the claws are very small and have a tendency to reduction and one species, Zambedania argentiniana has only one claw on tarsus IV. Theriadania venusta sp. nov. has an unusual fan-like shape of seta d of femur I. In most neopygmephorid genera this seta is hook-like, relatively short, setiform  in Singhalophorus and Nipponophorus, and very long and strongly barbed in Zambedania. Theriadania venusta sp. nov. is also characterized by the absence of the solenidion ω 2 . The absence of solenidion ω 2 in Neopygmephoridae is currently known only in Zambedania. Both C. tubulosa sp. nov. and T. venusta sp. nov. are characterized by an unusually long and thin empodium on tarsus IV and modification of some leg setae, especially d of tibia, tc' and pl" of tarsus on leg II. These characters are unknown in all other neopygmephorid mites. However, similar modification of the setae on leg II and a very long and narrow empodium is known in some species of Pygmephorus (Pygmephoridae), which also associated with small mammals (see Fig. 3 in Smiley and Whitaker, 1984). There is no doubt that these characters appeared in Neopygmephoridae (Crossdania and Theriodania) and Pygmephoridae (Pygmephorus) independently as a result of phoresy on small mammals.