Three new species and new records of Pediculaster (Acari: Pygmephoridae) from Western Siberia, Russia

Three new species of Pediculaster : P. tjumeniensis sp. nov. , P. bisetus sp. nov. , and P. rarus sp. nov. are described from rotting wood in Western Siberia. P. tjumeniensis is described based on phoretic and non-phoretic females and larva; P. bisetus and P. rarus are described based on phoretic females only. Pediculaster camerikae Khaustov, 2008, P. montanus Khaustov, 2008, and P. dudinskyi Khaustov, 2011 are recorded for the first time from Asia, the latter species is also recorded for the first time from Russia. Unusual character states of P. tjumeniensis larva are discussed.


Introduction
The genus Pediculaster Vitzthum, 1931 (Acari: Pygmephoroidea) is one of the largest in the family Pygmephoridae and comprises more than 100 described species in the world fauna (Khaustov et al. 2014;Khaustov 2015).Pediculaster-mites are fungivorous and inhabit a great variety of habitats, e.g.soil, litter, mosses, dung, nest material, decaying organic material (Camerik and Kheradmand 2010).Several species are considered as pests of mushrooms in commercial mushroom-houses (Cross and Kaliszewski 1988).Mites of the genus Pediculaster are characterized by the presence of two morphologically different forms of females: nonphoretic or "normal" and phoretic (Camerik et al. 2006;Martin 1978).Most Pediculaster species are phoretic on various Diptera, especially associated with cattle dung (Camerik 2010).
Little is known about Pediculaster mites inhabiting rotting wood and forest litter.Only few species were described from rotting wood: P. fusarii (Smiley and Moser, 1976) collected from the galleries of bark beetles from USA (Smiley and Moser 1976), P. dudinskyi Khaustov, 2011 collected from a tree hole from Ukraine (Khaustov 2011), P. ermilovi Khaustov, 2015 andP. lignarius Khaustov, 2015 collected from rotting wood in Western Siberia (Khaustov 2015).Khaustov (2015) reviewed mites of the genus Pediculaster of Russia and provided the key to phoretic females of Palaearctic species.Only two species, P. ermilovi and P. lignarius have been described and recorded from Western Siberia so far.
During the study of heterostigmatic mites of Western Siberia, three new species of Pediculaster were found in the samples of rotting wood.Moreover, three species, P. dudinskyi Khaustov, 2011, P. camerikae Khaustov, 2008b, and P. montanus Khaustov, 2008b were recorded from the Asia for the first time.

Materials and methods
Mites were collected from samples taken from decaying trees and cow dung, using Berlese funnels.They were posteriorly cleared in lactic acid and mounted in Hoyer's medium.The terminology for 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 ( , 2008a)).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 illumination.Photomicrographs were taken with Hitachi KP-HD20A digital camera.
Differential diagnosis -Phoretic female of the new species is most similar to P. sellnickianus (Rack, 1964) and P. limosinae Samsinak, 1984 (not separable morphologically from P. sellnickianus) by the presence of three pairs of setae on coxal fields I and II, setae ps 2 longer than ps 3 , and setae 2a much longer than 2b.The new species can be distinguished from P. sellnickianus by having setae c 2 clearly longer than c 1 (setae c 1 and c 2 subequal in P. sellnickianus), by the presence of ap5 (ap5 absent in P. sellnickianus), and setae e no more than twice longer than h 2 (setae e more than 3 times longer than h 2 in P. sellnickianus).Non-phoretic female of the new species is most similar to P. permagnus (Rack, 1971) but can be distinguished from it by longer distance between setae e and f, which less than 3 times shorter than distance f-f (e-f about 4 times shorter than f-f in P. permagnus), by solenidion φ 2 distinctly longer than φ 1 (solenidia φ 2 and φ 1 subequal in P. permagnus), and by much longer solenidion ω 2 , which reaching far beyond the base of solenidion ω 1 (solenidion ω 2 , much shorter and not reaching base of solenidion ω 1 in P. permagnus).Larva of the new species can be distinguished from all described larvae of Pediculaster by the presence of setae n on subcapitulum (setae n absent in all described larvae of Pediculaster).
Type deposition -The holotype and 2 phoretic female paratypes are deposited in the Etymology -The name of the new species is a combination of two Latin words bi meaning two and seta meaning bristle and refers to presence of two pairs of setae on coxal fields II.
Differential diagnosis -The new species is most similar to P. athiasae (Wicht, 1970) by the presence of three pairs of setae on coxal fields I, two pairs of setae on coxal fields II, subequal setae v 1 and v 2 and well-developed ap5.The new species can be distinguished from the latter in having one-chambered stigmata (two-chambered in P. athiasae), by smooth setae e (setae e barbed in P. athiasae), by the absence of seta on trochanter IV (trochanter IV with seta in P. athiasae), and distinctly shorter dorsal body setae (dorsal body setae distinctly longer in P. athiasae).
Non-phoretic female, male and larva unknown.Type deposition -The holotype is deposited in the collection of the Zoological Institute of RAS, Saint Petersburg, Russia.
Etymology -The name of the new species is derived from Latin rarus meaning rare and refers to its rareness.
Remark -The new species is described based on single specimen.However, it is in good condition and very well differs from closely related species.All attempts to collect additional specimens were unsuccessful.
Differential diagnosis -The new species is most similar to P. chistyakovi Khaustov and Ermilov, 2008 by the presence of three pairs of setae on coxal fields I and II, setae ps 3 distinctly longer than ps 2 , setae v 1 and v 2 subequal, and setae 2b much longer than 2a.The new species can be distinguished from the latter in having setae sc 2 , c 2 , f, and h 1 blunt-ended (setae sc 2 , c 2 , f, and h 1 pointed in P. chistyakovi), by setae ps 2 situated distinctly anteriad ps 1 (setae ps 2 and ps 1 situated on the same level in P. chistyakovi), by much shorter setae d on femur and tibia IV which not exceed beyond tip of tarsus (setae d on femur and tibia IV very long and exceed beyond tip of tarsus in P. chistyakovi), and by the presence of ap5 (ap5 absent in P. chistyakovi).Pediculaster dudinskyi Khaustov, 2011 Pediculaster dudinskyi Khaustov, 2011, 265, Figs 1-5.Phoretic female of this species was described from a tree hole of poplar in Western Ukraine (Khaustov 2011).This is the first record of P. dudinskyi from Asia and Russia.Material examined -One phoretic female, Russia, Tyumen Province, Tyumen, "Zatyumenskiy park", 57°09' N, 65°26' E, in the rotting log of birch, 26 April 2019, A.A. Khaustov leg.

Discussion
Larval stage is currently described only for five species of Pediculaster: P. fusarii (Smiley and Moser, 1976), P. mesembrinae (Canestrini, 1881), P. morelliae Rack, 1974, P. permagnus (Rack, 1971), and P. pseudomanicatus Camerik, 2001 (Smiley andMoser 1978;Martin 1978;Camerik 2001;Camerik et al. 2006).All described larvae are very similar morphologically and differ mainly by the lengths of setae and number of cheliceral setae (setae chb present or absent).The description of larva in P. tjumeniensis sp.nov.revealed several unusual characters.The most remarkable is the presence of two pairs of subcapitular setae (setae n present).The presence of subcapitular setae n is unknown in all described pygmephoroid mites, including available descriptions of larval stages.Occasionally, the abnormal seta n was recorded in adult female of scutacarid mite Pygmodispus latisternus Paoli (Khaustov 2008a).In larva of P. tjumeniensis sp.nov.subcapitular setae n present in all seven studied larvae and undoubtedly is not abnormal.The presence of this plesiomorphic character is most likely a result of an evolutionary reversion rather than retention.Other unusual characters found in P. tjumeniensis sp.nov.larvae are the absence of the solenidion on tibia III and spiniform seta pl" on tarsus III.These characters could be used in the future not only for separation of species but probably also for creating of species-groups or subgenera in the genus Pediculaster.
Claws and empodium as on tarsus II.Solenidion φ absent.Seta pl" of tarsus spine-shaped, smooth; setae d, v' of femur and l' of genu blunt-ended and barbed, other leg setae pointed and barbed.Femur not divided into basi-and telofemur.Male unknown.Type material -Phoretic female holotype slide ZISP T-Pygm-004: Russia, Tyumen Province, Tyumen, "Zatyumenskiy park", 57°09' N, 65°26' E, in the rotting log of birch, 21 April 2019, A.A. Khaustov leg.Paratypes: 7 phoretic females, same data as holotype; 4 phoretic and 4 non-phoretic females, same locality and collector, 10 July 2019; 2 phoretic females and 7 larvae, same locality and collector, 26 April 2019.Type deposition -The holotype and 4 phoretic females paratypes are deposited in the collection of the Zoological Institute of RAS, Saint Petersburg, Russia; other paratypes are deposited in the mite collection of the Tyumen State University Museum of Zoology, Tyumen, Russia.

Figure 13 Figure 14
Figure 13 Pediculaster rarus sp.nov., phoretic female: A -dorsum of the body, B -venter of the body.Legs omitted.