Torrenticolid water mites from Korea and the Russian Far East

Abstract New records of water mites of the family Torrenticolidae Piersig, 1902 (Acari: Hydrachnidia) from streams in South Korea and the Russian Far East are presented. Detailed descriptions or redescrptions are provided for eight species of the genera Torrenticola Piersig, 1896 and Monatractides K. Viets 1926. Two species are described as new to science: Torrenticola kimichungi sp. n. and Monatractides abei sp. n. Five species are reported as first records from Korea: Torrenticola brevirostris (Halbert, 1911); Torrenticola dentifera Wiles, 1991; Torrenticola recentis Tuzovskij, 2003; Torrenticola ussuriensis (Sokolow, 1934); and Torrenticola turkestanica (Sokolow, 1926). Torrenticola nipponica (Enami, 1940) is reported for the first time from Russia.


introduction
Water mites of the family Torrenticolidae are presently known from all continents except Antarctica, with more than 400 species described so far (Zhang et al. 2011, Pešić and Smit 2012a,b, Pešić et al. 2012. However, as the family has its maximum diversity in the still strongly understudied tropical areas, the species number is possibly higher by one order of magnitude . In general, torrenticolid mites are heavily sclerotized, dorso-ventrally flattened, crawling species which colonize running waters with well oxygenated sand and gravel substrates where proto-and tritonymphs can survive the quiescent phase of their life cycle (Di Sabatino et al. 2003).
At present, only one species of the genus Torrenticola Piersig, 1896, i.e. T. nipponica  is known from South Korea (Chung and Kim 1995), while five species, i.e., T. abbreviata (Sokolow, 1934), T. amplexa (Koenike, 1908), T. elliptica Maglio, 1909, T. recentis Tuzovskij, 2003 andT. ussuriensis (Sokolow, 1934), are known from the Russian Far East (Sokolow 1934, Semenchenko 2010. During a recent survey many specimens of the family Torrenticolidae were collected throughout South Korea and identification of this material was entrusted to the senior author. This research is part of the project aimed at uncovering Korean invertebrate diversity, and led by the National Institute of Biological Resources (NIBR). The identification of the material from the Russian Far East was made by second author. Eight species of the genera Torrenticola Piersig, 1896 and Monatractides K.Viets, 1926 are identified, two of them are new to science. Descriptions and redescriptions of these species are given in this paper.

Material and methods
Water mites were collected by hand netting, sorted on the spot from the living material, preserved in Koenike's fluid and dissected as described elsewhere (e.g. Gerecke et al. 2007). One sample from the Tigrovaya River (Russian Far East) was obtained via a hand-pump (similar to the Bou-Rouch method) from subterranean waters. A metal tube was hammered into river sediments to a depth of about 30 cm. Pumped samples were filtered through the hand net and fixed in 70 % ethanol for further examination in the laboratory under a stereo microscope. Holotypes and some paratypes are deposited in the National Institute of Biological Resources, Korea (NIBR); other paratypes (material from the Russian Far East) in the research collections of the Institute of Biology and Soil Science, Vladivostok, Russia (IBSS).
Remarks. The single male specimen examined from a stream in Naebyeansan National Park fits well the original description of Torrenticola brevirostris. The differences are found in a minor idiosoma and gnathosoma dimensions and a more shallow gnathosoma with a relatively less shortened rostrum compared with the populations from the Western Palaearctic (see: Cicolani and Di Sabatino 1990, Pešić et al. 2006, Di Sabatino et al. 2010). In the shape of gnathosoma the specimen from Korea matches the description of T. brevirostris from Gifu Prefecture in Japan (Imamura 1953). This may suggest that there is some degree of genetic isolation between the populations from the Far East and populations from the Western Palaearctic. However, understanding of these populations is not possible without additional material and probably will require the application of molecular techniques.
Distribution. Malaysia (Wiles 1991(Wiles , 1997  Diagnosis. Idiosoma elongated (dorsal shield L/W ratio 1.5-1.6); medial suture line of Cx-II+III in male short (L 74-85 μm); suture line of Cx-IV extended posterior to the genital field; excretory pore posterior to the line of primary sclerotization, Vgl-2 posterior to excretory pore; male genital field with maximum width at the anterior margin; gnathosoma deep with a short rostrum; P-4 with ventral setae on flat hump.
Description. General features. Idiosoma elongated; Cxgl-4 subapical; suture line of Cx-IV evident and curved, starting posterior from genital field, laterally curved anteriorly (Figs 3B,4B); excretory pore posterior to the line of primary sclerotization, Vgl-2 posterior to excretory pore; gnathosoma deep with a short rostrum not evidently set off from gnathosomal base (Fig. 3F); P-2 ventrally slightly convex, ventrodistal projection cone-shaped, pointed towards distal, P-3 with ventrodistal projection slightly larger than projection of P-2, P-4 slightly curved, ventral setae (one long and three short) on flat hump (Figs 3D-E, 4C). Male: Medial suture line of Cx-II+III short; genital field with maximum width at the anterior margin; ejaculatory complex normal in shape (Fig. 3C); P-2 and P-4 almost equal in length.

Etymology. The species is named after Drs Il-Hoi Kim and Kyung-Sook Chung in appreciation of their studies of the Korean water mites.
Remarks. The new species belongs to the group of species characterized by having well-developed finger or peg-like ventrodistal tubercles on P-2 and P-3, the deep gnathosoma with a short rostrum, not evidently set off from gnathosomal base and a relatively short medial suture line of Cx-II+III in male. This group includes the following Asian species of Torrenticola: T. brevirostris (Halbert, 1911) (Palaearctic), T. nanshihensis Pešić  Pešić et al., 2012 (Taiwan), T. retractipora Lundblad, 1969 (Burma), T. siamis Pešić & Smit, 2009 (Thailand), and T. subterranea Imamura, 1957 (Japan). Males of Torrenticola brevirostris and T. nanshihensis differ in a prominent suture line of Cx-IV starting at a right angle from the genital field, excretory pore on the same level as Vgl-2 and more away from the line of primary sclerotization and P-4 stockier with well developed ventral tubercles (see: Di Sabatino et al. 2010 for T. brevirostris, andPešić et al. 2012 for T. nanshihensis). Torrenticola projectura clearly separates in having P-3 with a long tapering ventral protrusion which curves distally (Pešić et al. 2012a). Males of Torrenticola retractipora can easily be distinguished by larger dimensions of the idiosoma, a differently shaped ejaculatory complex with large proximal chamber (see : Lundblad 1969), and a moderately long median suture line of Cx-II+III (101 μm, data taken from Wiles 1997). Torrenticola subterranea, a weakly defined species known from subterranean habitats in Japan (Imamura 1957(Imamura , 1959 is similar in Cx-IV extended posterior to the genital field, but differs in narrower frontal platelets, excretory pore and Vgl-2 lying on the margin of primary sclerotization, and a less developed distoventral projections on P-2 and P-3 (see: Imamura 1959). Torrenticola siamis closely resembles T. kimichungi sp. n. in the general shape of idiosoma and palp, but males are distinguishable in having Cx-IV not extended posterior to the genital field and the genital field more elongated (L/W ratio 1.4, data taken from Pešić and Smit 2009) and rectangular in shape.
Habitat. A permanent sandy/bouldery stream with considerably exposure to sunlight (Fig. 14C); the specimens from Russia were collected from interstitial waters.
Distribution. South Korea, Far East of Russia (present study).
Remarks. The male specimens from South Korea and Russia fit the description of Torrenticola nipponica  which was based on one male and seven females from River Inôzava, Uzi region in Japan . However, as the type material was probably lost (not found in the arachnid collection in the National Museum of Nature and Science, Tokyo, Hirotsugu Ono pers. comm.) additional sampling and selection of a neotype from the locus typicus is necessary to guarantee taxonomic stability of T. nipponica. In the original description,  compared T. nipponica with T. brevirostris (Halbert, 1911), a species which differs in the gnathosomal rostrum not distinctly set off from the gnathosomal base, P-2 shorter than P-4, the suture line of Cx-IV starting at right angle from the genital field, the excretory pore and Vgl-2 more distanced from the line of primary sclerotization and the genital field in male is less elongated.
Habitat. A permanent shaded sandy/bouldary stream at low elevations (Fig. 14A); the specimens from Russia were collected from interstitial waters.
Remarks. The specimens from South Korea fit the description of Torrenticola recentis, a species described by Tuzovskij (2003) from the Primory Territory in the Russian Far East, and later on reported by Semenchenko (2006) from the River Kedrovaya in the southern part of Primory Territory and from many other southern and northern rivers in the Primory Territory (Semenchenko 2010). The specimens examined from River Kedrovaya agrees well with our specimens due to colour pattern of dorsal shield and length of medial suture line of Cx-II+III, characters not given by Tuzovskij (2003) in the original description of T. recentis.
Torrenticola elliptica Maglio, 1909, a species similar in general shape of idiosioma and palps, differs from T. recentis in a more slender idiosoma, a more extended postgenital area in the male and the ejaculatory complex with a large proximal chamber (see: Di Sabatino et al. 2010). Possibly T. recentis was misidentified as T. elliptica in many old records from the Russian Primory Territory (e.g. Sokolow 1934). Likewise, old records from Japan ) might refer to T. recentis.
Remarks. Torrenticola ussuriensis was originally described by Sokolow (1934) from the Primory Territory in the Russian Far East, and later reported from River Inôzava in Japan . Recently this species was redescribed by Pešić et al. (2011) based on new material from the Russian Far East. A single female specimen examined from River Inje agrees well with the redescription of T. ussuriensis. The only difference is found in the excretory pore lying on the same level as Vgl-2 in specimen from Korea while in specimens from Russia and Japan (see ) the excretory pore is shifted slightly posterior to Vgl-2.
Distribution. Far East of Russia (Primory and Khabarovsk Territory, Jewish Autonomous and Amurskaya Area -"Atractides semisutus " Sokolow 1934;Pešić et al. 2011); Japan (Uzi region -"A. semisutus . New for the fauna of Korea. Morphology. General features. Idiosoma elongated (dorsal shield L/W ratio 1.5-1.6); dorsal shield with colour pattern as illustrated in Figs 11G-H; Cxgl-4 subapical; gnathosoma ventral margin strongly curved; P-2 ventral margin convex, P-2 and P-3 with a subrectangular, apically serrated ventrodistal projection, P-4 stocky with well developed ventral protuberance bearing one long and three short setae (Figs 10C-D). Male: Medial suture line of Cx-II+III moderately long; genital field subrectangular in shape, ejaculatory complex normal in shape; excretory pore and Vgl-2 located on the margin of primary sclerotization. Female: Posterior suture line of Cx-IV curved and well evident; genital field excretory pore and Vgl-2 away from the line of primary sclerotization.
Remarks. The specimens examined from River Inje fit the description of Torrenticola turkestanica, a species described based on a single female from Tadjikistan (Sokolow 1926). The only difference with the original description is found in a broader genital field in the type specimen. Later on, populations provisionally assigned to T. turkestanica, mainly based on the approved non-identity with the alternative species, were reported from Indian Himalayas (Pešić et al. 2007) and Thailand (Pešić and Smit 2006). The populations from Thailand differ from our material and the original description in a less slender idiosoma (dorsal shield L/W ratio 1.3-1.4, data taken from Pešić and Smit 2006), a much shorter ventral seta on P-2 and more slender P-4, and very likely represent an new species. The additional material and finding of a male from the locus typicus is necessary to clarify the taxonomy of T. turkestanica (the holotype may be missing, not found in the Zoological Institute of St. Petersburg, Denis Tumanov pers. comm).
Torrenticola japonica Imamura, 1953, a species described based on a single female from a stream in Shinjô-mura in Japan (Imamura 1953), resembles T. turkestanica in the characteristic shape of the palp (ventral margin of P-2 convex, P-2 and P-3 with subrec-tangular ventrodistal projection). From the latter species, T. japonica differs in a broader idiosoma, a dorsal shield with broader shoulder platelets and posterior suture line of Cx-IV not extending far beyond genital field (see : Imamura 1953). However as the holotype of T. japonica is probably lost (Hiroshi Kajihara, pers. comm), additional material and selection of a neotype from the locus typicus is necessary to clarify its taxonomy. Imamura (1953) reported a single male of Torrenticola elliptica Maglio, 1909, from a stream in Shinjô-mura in Japan. However due to the presence of subrectangular   (Sokolow, 1940), female (D specimen photographed immediately after dissection E-F specimens mounted in Hoyer's medium): D-E specimen from Korea F specimen from Russia G-h Torrenticola turkestanica (Sokolow, 1926), specimens from River Inje, Korea: G male h female i Monatarctides abei sp. n., male holotype. Photos. V. Pešić (Figs A-B, D-E, G-I), K. Semenchenko (Figs C, F). ventrodistal projections on P-2 and P-3 and a convex ventral margin of P-2, his illustrations show a general conformity with Torrenticola japonica and T. turkestanica. It is very likely that the specimen attributed by Imamura (1953) to T. elliptica is conspecific with T. japonica, especially as both species were collected from the same location and on the same day.
Habitat. A permanent sandy/bouldery river with considerable exposure to sunlight (Fig. 14E).
Distribution. Tadjikistan (Sokolow 1926), Indian Himalayas (Pešić et al. 2007), Thailand (Pešić and Smit 2006, but see remarks above). New for the fauna of Korea. Diagnosis. Lateral margins of dorsal shield nowhere subparallel; distal margins of P-3 with several pointed extensions; genital field in male with slightly protruding anteriolateral angles; medial suture line of Cx-II+III in female relatively long (L 90-105 μm).
Female (from CR2, in parentheses specimen from Russia). Idiosoma (ventral view: by NIBR Korea (NIBR No. 2013-02-001), and by the Presidium of FEBRAS grants 13-III-B-06-047, and the Russian Foundation for Basic Research grant 09-04-98544. We are thankful to an anonymous referee for the careful work and valuable comments.