CHECKLIST OF THE WATER MITES (ACARI, HYDRACHNIDIA) OF KOREA, WITH DESCRIPTION OF ONE NEW SUBGENUS AND TWO NEW SPECIES

Using published records and original data, a checklist was compiled of the water mite (Acari, Hydrachnidia) fauna of Korea. The total number of species and subspecies recorded from Korea up to date is 74 species, in  32 genera and 13 families. One new subgenus, Orientmomonia , and two new species are described: Albia ( Albiella ) kseniae and Momonia ( Orientmomonia ) koreana ; the first description of the male is given for Atractides gracilis (Sokolow, 1934). Woolastookia concava Kim & Chung, 1996 is synonymized with W. elongata (Sokolow, 1934). Additionally, first records for Korea are given for Panisopsis orientalis Imamura & Mitchell, 1967, Hydrodroma torrenticola (Walter, 1908), Hygrobates (Hygrobates) longiporus Thor, 1898, and Arrenurus ( Truncaturus ) sp. near corsicus (E. Angelier, 1951).


Material and Methods
The data from all publications which contain data on distribution of water mites in South Korea are included in the systematic part of this paper. The species referred to in postgraduate theses and scientific meetings are no formal publications and are consequently not included.
For each species, the Korean provinces ( Fig. 1) are listed where the species has been collected. The names of the species are in accordance with the most recent literature (e.g., Davids et al. 2007, Di Sabatino et al. 2010. For new records, water mite were collected by hand netting, sorted on the spot from the living material, conserved in Koenike's fluid and dissected as described elsewhere (e.g., Gerecke et al. 2007). Holotypes will be deposited in the National Institute of Biological Resources, Korea (NIBR).
Remarks. The description of Atractides gracilis was based on a single female from the Primory Territory, in Russian Far East. Later on, female A. gracilis were reported by  from Japan and Kim and Chung (1991) from Korea, but until now no males have been found. The specimens from Korea match the original description, and the following characters of the males collected together with female A. gracilis indicate conspecifity: long and very slender I-L-6, setae S-1 and -2 heteromorphic and widely distanced, excretory pore slightly sclerotized, palp with P-2-3 ventral margins straight, and slender P-3 (L/H ratio 3.1-3.6) and P-4 (L/H ratio 6.0-6.6).   Etymology. Named after Ksenia Semenchenko (Vladivostok, Russia), for her contribution to the taxonomy of water mites. Remarks. Due to the similar configuration of coxal suture lines and shifting of Cxgl-4 anterior to IV-L insertions, the new species is most similar to A. vanimoensis Wiles, 1992 andA. papuaensis Smit, 2013, from Papua, New Guinea, both only known in the female sex (see Wiles 1992 andSmit 2013, respectively).
The new species can be distinguished from the abovementioned species by the different colour pattern (dorsal shield posteriorly with a rose tinge in A. papuaensis, a blue band across the middle of the dorsal shield in A. vanimoensis) and by having a spine-like seta on Cx-II and Cx-III. Albia papuaensis (in parentheses data taken from Smit 2013), is similar in a broader idiosoma (L/W ratio 1.32), and L2 lying anteromedially to L1, but differs in minor idiosoma and palp dimensions (L idiosoma 664, P-2, 60; P-4, 62). A. vanimoensis differs in a more slender idiosoma (L/W ratio 1.59) and L2 lying anterior, but both median (Wiles 1992).
Habitat. A small sandy/bouldary pool near the main stream, shaded by riparian vegetation (Fig. 11). Distribution. South Korea; known only from the type locality.  Remarks: This species, recently described from the Primory Territory in the Russian Far East, can be distinguished from L. japonica Imamura, 1956 (described after a single male from Japan, Imamura 1956) by the posterior pair of setae on dorsal shield associated with glandularia, the excretory pore located dorsally, the complete median suture line Cx-II/III, P-3 dorsoproximal setae considerably shorter than dorsodistal setae, and presence of a transverse suture line between the middle of the lateral margin of the Cx-IV and the lateral margin of the ventral shield (Tuzovskij 2012). Kim and Chung (1996) reported and illustrated L. japonica from Korea. As their illustrations (Kim and Chung 1996: Figs. 12, 13A-B) show a general conformity with L. orientalis in all abovementioned characters, it is very likely that the specimens attributed to L. japonica refers to L. orientalis.

Family LETHAXONIDAE Cook, Smith & Harvey, 2000 Genus Lethaxona K.Viets, 1932
Lethaxona hyogoensis Imamura, 1956 Records from Korea: Gangwon Province - Kim and Chung (1996) Cook 1974); dorsal shield composed of small anterior and a large posterior plate, flanked by ring composed of 7 pairs of platelets, with 1th, 2nd, 4th, 5th, 6th and 7th pairs bearing glandularia, and 4 pairs of tiny sclerites bearing slit organs. Type species. Momonia koreana n. sp. Remarks. The genus Momonia includes six species from three subgenera. The typical subgenus is known from Europe (one species) and North America (three species). Two other subgenera are monotypic, Momonia karelica (Sokolow, 1926), type species of the subgenus Kondia Sokolow, 1926, is known from two female specimens from Russia and Sweden; M. fuscina Yi & Jin, 2012, type species of the subgenus Paramomonia Yi & Jin, 2012, was described in both sexes from China (Yi & Jin 2012). In these three subgenera, the idiosoma varies from mostly membranous, lacking extensive shields (Kondia) to heavily sclerotized, with dorsal and ventral shields, dorsal shield entire (Paramomonia) or consisting of anterior and posterior plates (Momonia s.s.). The new subgenus resembles Momonia s.s. due the presence of a two-parted dorsal shield but differs in a ring composed of 7 pairs of platelets flanking anterior and posterior plates of dorsal shield. The cyclic arrangement of dorsal platelets appears to represent a unique evolutionary development that does not indicate close relationship with other known subgenera. Diagnosis. As for subgenus.

Description
Male -Colour greenish. Idiosoma oval in shape. Sclerotized plates wrinkled. Lateral eyes enlarged. Dorsum with a transverse anterior plate bearing postocular setae, its anterior margin forming a shallow bay for the unpaired frontal organ, and a large, longitudinally wrinkled posterior plate; anterior and posterior plates flanked by ring composed of 7 pairs of platelets, with 1th, 2nd, 4th, 5th, 6th and 7th pairs bearing glandularia, and 4 pairs of tiny sclerites bearing slit organs (Figs. 5D, 8A).
Venter nearly covered by ventral shield (Fig. 8B); Cx-I+II with distinct medial edges, separated from remainder of venter by an articular membrane; Cxgl-1 located on anterolateral corner of Cx-III, medial margin of Cx-III much longer than medial margin of Cx-IV, Cx-IV with rounded projections covering the IV-L-insertions and on each side a field of about 12 -16 curved setae in posterolateral part, Cxgl-4 located between Cx-IV and genital field. Genital field (Fig. 5F) subterminal, lying between Cx-IV, with three pairs of acetabula in gonopore; 6-8 pairs of genital setae around gonopore; excretory pore and flanking glandularia widely fused to ventral shield.
Palp (Figs. 5E, 9F-G): dorsal setae of P-2 and P-3 long and slender, P-4 with a small anterodorsal peg-like seta, two thick ventral setae on a prominent tubercle and four dorsal hair-like setae; P-5 slender, with one main claw flanked by three shorter ones.

Female -unknown.
Etymology. Named after the country where the new species was detected. Habitat. A small sandy/bouldary pool near the main stream, shaded by riparian vegetation (Fig. 11). Distribution. Korea; known only from the type locality.

Genus Stygomomonia Szalay, 1943
Stygomomonia rotunda Imamura, 1956 Records from Korea: Gangwon Province - Chung and Kim (1997). Remarak. The posterior margin of genital plate of the illustrated male specimen from Korea assigned by Kim and Chung (1991) is clearly concave, not deeply indented as in F. zschokkei. Due to the location of ventral setae on III-L-6 in the distal part, the specimen from Korea resembles F. brevipes Walter, 1907 (Europe), but differs in less slender dorsal shield in the male (L/W 1.2, calculated from figure; Kim and Chung 1991 : Fig. 7H). The taxonomic status of these specimens should be verified by additional material. Imamura, 1956 Records from Korea: Gangwon Province -"Ljania bipapillata" Chung and Kim (1991); Gangwon Province - Kim and Chung (1996). Remarks: See Remarks under Ljania orientalis.

Discussion
At the present state of knowledge, the number of species and subspecies of water mites recorded from Korea is 74, in 32 genera and 13 families; 17 of these species (23%) are indicated as being endemic. The documentation of the water mite fauna in Korea is askew (Table 1). Only from one province (Gangwon) more than 50 species is known. Two provinces Jeollabuk and Jeollanam have 13 and 10 species, respectively, and from the remaining provinces less than 10 species are known.
Compared with the number of water mites in some neighboring areas, such as Japan (223 species and 41 subspecies -Abé 2005), China (193 -Jin et al. 2010) and Russian Far East (217 species and 6 subspecies -Semenchenko 2008) we can conclude that the number of 74 species is far below a reliable estimation and further research undoubtedly will increase the number of species known from Korea. The publication of this checklist should help to stimulate further studies on this important but still not well studied group of invertebrates.