New records of the water mite genus Hygrobates Koch, 1877 from Kyrgyzstan (Acari, Hydrachnidia, Hygrobatidae), with the description of one new species

The present study is based on material collected in August 2013 during a collecting trip of the authors to Kyrgyzstan. Hygrobates tienshanensis n. sp . is described based on males collected from two springs in Tian Shian Mountains, at altitudes of 1750-2100 meters. In addition, new records of H. kirgizicus Sokolow, 1935 and H. bucharicus Sokolow, 1928 are given.


Introduction
Water mites of the genus Hygrobates Koch, 1877 are common in running and standing waters and have been found in all biogeographical regions except Antarctica (Gerecke et al. 2016;Pešić et al. 2017). In the Palaearctic, in addition to the nominate subgenus, the genus comprises species of Rivobates Thor, 1897. Most of the species of the latter subgenus have a preference for spring habitats and cold water streams, but some species, e.g., H. zawali Pešić, 2015, are typical lake inhabitants, found at a depth of 80 meters (Pešić 2015). Recently, several species groups of Hygrobates s. str. have been intensively studied, applying an integrative approach combining traditional morphology and the analysis of DNA barcodes, proving the existence of a number of previously overlooked species, and showing that traditionally defined morphospecies such as H. fluviatilis (Ström, 1768), H. longipalpis (Hermann, 1804) and H. nigromaculatus Lebert, 1879 (see Pešić et al. 2017Pešić et al. , 2019aPešić et al. ,b, 2020 in fact are representing species groups. The present study is based on material collected by the authors during a joint collecting trip from 1-15 August 2013 to Kyrgyzstan. So far, the hygrobatid water mite fauna of this region is poorly known. It includes four recently described new species of the genus Atractides (A. grigorievkae Pešić & Smit, 2018, A. manasi Pešić & Smit, 2018, A. alaarchaensis Pešić & Smit, 2018and A. sonkulensis Pešić & Smit, 2018 but no water mites of the genus Hygrobates (see Pešić and Smit 2018 for an overview of water mites fauna of Kyrgyzstan). In this paper, the description of one new species of the subgenus Rivobates and new records of Hygrobates (s. str.) kirgizicus and H. (s. str.) bucharicus are given.

Material and Methods
Water mites were collected with a 250 µm mesh size-hand net, sorted live in the field, and preserved in Koenike's fluid. Morphological nomenclature follows Gerecke et al. (2016). The holotype and paratypes of the new species will be deposited in Naturalis Biodiversity Center in Leiden (RMNH). In the section "Material examined" collecting, collectors of all material are Smit & Pešić, site abbreviations derive from the geographical database Pešić.

Systematics
Measurements. Male (n=1) -Idiosoma: L 975, W 800; coxal field: L 453; Cx-III W 575; mL of Cx-I + gnathosoma L 377; distance between lateralmost ends of Cx-II apodemes, 175; genital field L/W 225/181, ratio 1,24; L Ac-1-3: 61-66, 69, 70-75. Ejaculatory complex (Fig. 3E)     Remarks -Considering the morphology of palp and genital field, the specimens reported here agree with Hygrobates kirgizicus Sokolow, 1935, originally described from a tributary of the Chui River in the Ortotokoy valley, Kazakhstan (Tian Shian Mountains) at altitudes of 1700-1800 m. In addition, Sokolow (1935) reported the species from a depth of 10 m in Nizhneye Mul'tinskoye Lake (Altai, 1700 m asl, Russia). In regard to the shape of palp and idiosoma, H. kirgizicus is most similar to H. longipalpis (Hermann, 1804). For a long time, the latter had been considered a species with a Holarctic distribution, but a recent study conducted by Pešić et al. (2019) revealed within H. longipalpis the presence of two distinct lineages, with H. prosiliens Koenike, 1915, for a long time considered its junior synonym and now reestablished, having a preference for standing waters, and H. longipalpis s. str. inhabiting slow flowing sectors of running waters. From both species, H. kirgizicus can be separated in Cx-IV sub-triangular in shape, with anterior and posterior margins converging towards the median line.
Diagnosis -Posterior margin of Cx-I+II medially equally rounded; number of Ac low (5-10), anterior margin of genital field (L/W ratio 0.99) with a small knob-shaped medial projection, posterior margin with a well-developed protrusion in the centre of indentation, extending beyond posterior genital plate margin.  Description -Integument finely striated; dorsal and ventrocaudal idiosoma without sclerotized muscle insertions. Coxae in three groups; posteromedial margin of Cx-I+II rounded (Figs. 3A, 4A); medial margin of Cx-IV almost straight. Genital field (Figs. 3B, 4B) rather slender, L/W ratio 0.99, with 5-10 pairs of Ac, anterior margin convex with a small knob-shaped medial projection, posterior margin with a well-developed protrusion in the centre of indentation, extending beyond posterior genital plate margin. Palp: ventral margin of P-2 proximally almost straight, distally protruding in a nose-shaped projection bearing denticles; P-3 distoventrally slightly protruding, covered by denticles; P-4 ventral margin slightly projecting near the insertion of two ventral setae, ventral setae located close together (Figs. 3C-D).
Habitat -The collecting sites are weakly flowing rheocrenes strongly exposed to sunshine and with substrata dominated by decomposing plants and organic detritus.