Further studies on water mites from Korea, with description of two new species (Acari, Hydrachnidia)

Abstract New records of water mites (Acari: Hydrachnidia) from streams in South Korea are presented. Two species are described as new to science: Torrenticola neodentifera sp. n. (Torrenticolidae) and Atractides ermilovi sp. n. (Hygrobatidae). Five species are reported as first records for Korea: Wandesia (Wandesia) reducta Tuzovskij, 1987, Wandesia (Wandesia) cf. rara Tuzovskij, 1990, Sperchon (Sperchon) orientalis Tuzovskij, 1990, Feltria (Feltria) kuluensis Tuzovskij, 1988 and Atractides (Atractides) constrictus (Sokolow, 1934). The latter species is redescribed and elevated to species rank based on new material from the Russian Far East.


Introduction
The water mites of this study mainly were collected by the senior author during his trip in South Korea in May, 2013. The paper aims to describe this material in order to prepare the way towards the production of an identification key of this important group of freshwater invertebrates.

Material and methods
Water mite were collected by hand netting, sorted on the spot from the living material, fixed in Koenike-fluid and dissected as described elsewhere (e.g., Gerecke et al. 2007). Holotype and paratypes of the new species will be deposited in the National Institute of Biological Resources, Korea (NIBR); material from the Russian Far East is deposited in the research collections of the Institute of Biology and Soil Science, Vladivostok, Russia (IBSS).
In the section 'Material examined' collecting site abbreviations derive from the geographical database Pešić. The composition of the material is given as: males/females/deutonymphs. All measurements are given in µm. For a detailed description and discussion of the characteristics of the genus Atractides and a detailed methodological introduction, see Gerecke (2003).

Systematic part
Remarks. The single female from this study matches the general morphology of Wandesia reducta Tuzovskij, 1987. This species was described by Tuzovskij (1987) from Magadan region in the Russian Far East, based on three females and a larva.
Legs: setation as given in Fig. 2E-H; dorsal margin of I-L-6 and II-L-6 strongly concave ( Fig. 2E-F); dL of I-L-3-6: 95,118,123,123;111,120,122;191,109,121;129,122,123. Remarks. With regard to similar setation of coxae, P-5 without a flagelar seta and dorsal margin of the tarsus of I-L and II-L strongly concave, the new species resembles Wandesia rara Tuzovskij, 1990 a species described from the Primory Territory in the Russian Far East on the basis of a single deutonymph (Tuzovskij 1990). The difference is found in more elongated Ac (L/W 2.0, calculated from figure 38-1, of Tuzovskij (1990)) in the deutonymph of W. rara. Thus, our assignment of specimen from Korea is tentative. Only with more material in the future, and finding of a adults from the locus typicus it will be possible to decide whether the specimen from Korea is conspecific with W. rara or a species new for science.

Family Sperchontidae Thor, 1900 Genus Sperchon Kramer, 1877
Sperchon (Sperchon) orientalis Tuzovskij, 1990  Remarks. The specimens examined from South Korea matches the general morphology of Sperchon orientalis Tuzovskij, 1990, a species described from the Primory Territory in the Russian Far East (Tuzovskij 2008). Due to the general shape of idiosoma (Cx-I medially separated, excretory pore surrounded by a sclerotized ring, see Fig. 3B) and palp (P-4 ventral setae strongly developed and projecting, dividing this segment in three equal parts in size, Fig. 3C-D), S. orientalis closely resembles S. glandulosus Koenike, 1886, from which it differs by the eye capsule longer than diameter of Postoc., a higher number of dorsal setae on P-2 and -3 and less densely arranged dorsal setae on IV-L-3-5 (Tuzovskij 2008). Chung and Kim (1991) reported and illustrated Sperchon fluviatilis Uchida, 1934 from Korea. However, the excretory pore in S. fluviatilis is smooth (see Uchida 1934, fig. 12-13), not sclerotized as in the illustrated male specimen from Korea. As their illustrations (Chung and Kim 1991: fig. 3A-D) show a general conformity with S. orientalis, it is likely that the specimens attributed to S. fluviatilis refer to S. orientalis.
Description. General features -Idiosoma elongated; dorsal shield with colour pattern as illustrated in Fig. 6A,C; frontal platelets anteriorly bulging (Figs 4A, 5A); gnathosomal bay V-shaped; Cxgl-4 subapical, only slightly posterior of Cx-I tips; medial suture line of Cx-II+III long; posterior suture line of Cx-IV in its medial part perpendicular to the longitudinal body axis, laterally distinctly curving anteriorly; excretory pore and Vgl-2 on the line of primary sclerotization near posterior idiosoma margin; gnathosoma ventral margin only slightly curved, rostrum well developed; P-2 shorter than P-4, ventral margin of P-2 with a fine denticulation also in proximal half of the segment, distally with a laterally compressed, anteriorly directed hyaline extension and a very short, denticle-like seta laterally at base of projection; P-3 with a broad, subrectangular, apically serrated ventrodistal projection with a fine denticles, and a short seta laterally at base of projection; P-4 ventral tubercles well developed and separated (Figs 4C, 5C). Male. Genital field subrectangular; ejaculatory complex conventional in shape ( Fig. 2D in Pešić et al. 2013). Female. The short postgenital area and caudal position of the excretory pore (Fig. 5B) in the specimen from Korea are due to the obviously juvenile age (indicated by weak sclerotization and absence of eggs); genital field pentagonal in shape.
Etymology. Named for its similarity with T. dentifera Wiles, 1991. Remarks. Pešić et al. (2013) collected a single male from a stream in Naebyeansan National Park, South Korea and assigned it to Torrenticola dentifera. This specimen is in perfect agreement with specimens examined in our study. In the original description of T. dentifera, a species described on the basis of two males from Selangor, Peninsular Malaysia (Wiles 1991), no information on colour pattern of dorsal shield and shape of ejaculatory complex are given. At the present state of art, males of Torrenticola dentifera can be distinguished from the new species by smaller dimensions of idiosoma and palps, and a more slender ventrodistal projection on P-3.
Distribution. Korea ("Torrenticola dentifera" Pešić et al. 2013, this study (Sokolow, 1934) a species described from the Primory Territory in the Russian Far East (Sokolow 1934), and later on reported by Chung and Kim (1997) from Korea. This species is known from a female only making it difficult to separate from other similar species, i.e. H. ezoensis Uchida, 1934 (Russia: Sakhalin, Japan: Hokkaido) and H. taniguchii Imamura, 1954 (Japan, Hokkaido). In the original description Sokolow (1934Sokolow ( , 1940, in addition to more slender P-3 (compared with H. diversiporus), gave particular weight to the smaller dimensions of coxae which occupy one third of venter. According to Imamura (1954) H. taniguchii differs from H. microepimeratus in larger coxae. Hygrobates ezoensis differs in P-2 with a more pronounced and acute ventrodistal projection and stouter P-3 (see Matsumoto et al. 2005).
Remarks. Atractides constrictus was originally described by Sokolow (1934) from the Primory Territory in the Russian Far East as a 'variety' of A. nodipalpis. In the original description Sokolow (1934Sokolow ( , 1940 gave particular weigt to the shape of P-4 in males: strongly thickened near proximoventral seta, basally strongly narrowed, ventral setae more closely approaching to each other. However, there is no reason to support the placement of this taxon as a subspecies of A. nodipalpis, as from the latter species, A. constrictus can easily be distinguished by the fused Vgl-1 and -2. Males examined from Korea show a general conformity with material from the Far East of Russia. Differences are found in a more enlarged Ac-3, a larger S-1/2 interspace and I-L-6 relatively longer compared to I-L-5 in specimens from Korea. Distribution. Far East of Russia (Primory Territory -Sokolow 1934). New for the fauna of Korea.
Female: unknown. Etymology. Named after Dr Sergey Ermilov (Tyumen, Russia), for his contribution to the taxonomy of oribatid mites.
Remarks. The new species resembles Atractides samsoni (Sokolow, 1936) in the small S-1/2 interspace, I-L-6 stocky, postgenital area with smooth excretory pore and unfused Vgl-1/2 and a palp with a conus shaped ventrodistal protrusion in male. The latter species can be distinguished by the shorter medial suture line of Cx-I, smaller acetabula, more slender S-1 and -2, and I-L-6 only weakly curved and longer (see Gerecke 2003). Males of A. constrictus (Sokolow, 1934), a species similar in the shape of palp (double ventral protrusion on P-2), a larger Ac (maximum diameter > 39 µm), and I-L-6 relatively short compared to I-L-5 (L I-L-5/6 ratio 1.4-1.6), differ in wider setal interspace on I-L-5, I-L-6 more slender and more narrow centrally, P-4 ventral setae inserted more closely to each other and genital field deeply indented both anteriorly and posteriorly.
Habitat. A permanent sandy/bouldary stream, shaded by riparian vegetation (Fig. 13B) (Tuzovskij (1988). This species closely resembles F. minuta Koenike, 1892, a species known from central, northern and western Europe, due to the following features: dorsum in male with a large shield (including Postoc. and Dgl-1-3) and Dgl-4 on paired, transverse, laterally pointed posterodorsal platelets (fig. 7-1, in Tuzovskij 1988), genital plate in male with undulating or straight anterior margin, gonopore in central position, and more than 50 pairs of Ac scattered over the whole plate (Fig. 12A), and male IV-L-6 with a digitiform ventrolateral extension directed to distal part of segment (Fig. 12B). Feltria minuta differs in relatively more slender palp, P-4 with both ventral setae on slightly elevated, parallel longitudinal extensions, and male IV-L-6 relatively more shorter with ventrolateral extension bearing one fine seta and two enlarged, transparent setae, adpressed to each other and directed ventrally (Gerecke et al. 2009). Chung and Kim (1991) reported and illustrated Feltria ishikariensis Imamura, 1954 from Kangreung, Korea. This species was described orginally by Uchida (1934) as F. rotunda based on three specimens (probably, by mistake assigned to a male, see figs 48-49 in Uchida 1934). Later on, Imamura (1954) described and illustrated the female of F. ishikariensis from Hokkaido, Japan. Feltria ishikariensis clearly differs from the species illustrated by Chung and Kim (1991) by the lower number of acetabula (< 50 pairs of Ac). As their illustrations (Chung and Kim 1991: Figs 6G-I, 7A-C) show a general conformity with F. kuluensis in all abovementioned characters, it is very likely that the specimens attributed to F. ishikariensis refer to F. kuluensis.  In the same paper, Chung and Kim (1991) assigned two female specimens collected from Kangreung to F. minuta Koenike, 1892. As mentioned by Pešić (2014), because the important characters are restricted to males, this assignment is uncertain, and probably refer to female of F. kuluensis.
Distribution. Far East of Russia (Tuzovskij 1988). New for fauna of Korea.