Nonmarine Ostracoda (Crustacea) from Jeju Island, South Korea, including descriptions of two new species

Collections of brackish and freshwater ostracods on Jeju Island, South Korea, yielded 26 species, including two new species belonging to the genera Cyclocypris and Cypretta, and nine new records for the Korean fauna: Bradleytriebella tuberculata (Hartmann, 1964), Strandesia flavescens Klie, 1932, Potamocypris variegata (Brady & Norman, 1889), Heterocypris salina (Brady, 1868), Stenocypris hirutai Smith and Kamiya, 2006, Ishizakiella miurensis (Hanai, 1957), Terrestricythere ivanovae Schornikov, 1969, Limnocythere sp. and Tanycypris alfonsi Nagler, Geist and Matzke-Karasz, 2014. Tanycypris alfonsi is also known from Germany, where it is considered to be an alien species. The Limnocythere species belongs to the stationis group, which consists of another eight species, and is probably undescribed. A lack of males hinders its description, but its presence in Korea is significant; including the record herein, seven of the group inhabit North-East Asia, indicating the group may have originated in this region. http://zoobank.org/urn:lsid:zoobank.org:pub:74FA8742-D301-4EC0-B058-021EE1CDFCB0


Introduction
Jeju Island, the largest island in South Korea, lies approximately 80 km south of the Korean peninsula. The island is about 73 km across east to west and 31 km north to south, and covers an area of 1847 km 2 . It is a shield volcano, which started to form approximately two million years ago, and is dominated by Mount Halla, reaching 1950 m above sea level. The island mainly consists of basaltic and trachytic lavas, and underlying volcaniclastic deposits around the coasts. Natural surface waterbodies are not common on the island because rainwater readily percolates through the underlying volcanic geology; streams are usually dry except after heavy rainfall. The island has a humid subtropical climate, and is warmer than the rest of Korea.
Only six species of freshwater ostracods have been previously reported from Jeju Island: Heterocypris incongruens (Ramdohr, 1808), Dolerocypris fasciata (O.F. Müller, 1776), Dolerocypris sinensis Sars, 1903, Cypretta seurati Gauthier, 1929, Potamocypris mastigophora (Meuthuen, 1910) [as Potamocypris producta (Sars, 1924)], and Ilyocypris dentifera Sars, 1903(Kim and Min 1991a, 1991b. These species, collected from rice fields, ponds and bogs, represent a small fraction of ostracod diversity that would be Note: Sex determination of some species is not possible without dissection, and so for some samples the number of individuals of each sex is not given. coated with gold before being photographed with a JEOL 5800 LV scanning electron microscope (JEOL, Tokyo, Japan). Carapaces of Cypretta seurati used for measurements were first photographed using SEM, and the digital images then measured using the software ImageJ (Research Services Branch, National Institute of Mental Health, Bethesda, MD, USA; http://imagej.nih.gov/ij/). The type and figured material is deposited in the National Institute of Biological Resources (NIBR), Korea (numbers with prefix NIBRIV), and in the Department of Biological Science, Daegu University, Korea (numbers with prefix DB).

Results
Twenty-six species of brackish and freshwater ostracods were recovered, representing four superfamilies, and six families (Tables 1, 2). Two species are new and described herein.

Remarks
Candona quasiakaina was described from a mountain stream near Seoul, approximately 440 km to the north of Jeju Island . This species was found in small numbers (14 males, one female) from only one locality during our survey, a seep in a dried streamlet (locality 14). Physocypria nipponica Okubo, 1990 Paracypridinae Dolerocypria mukaishimensis Okubo, 1980 Cyprididae Cyprettinae Cypretta karanovicae n. sp.

Derivation of name
From the Greek, anakolos, meaning shortened or stunted, referring to the strongly reduced natatory setae of the antennae.

Diagnosis
Right valve overlaps left, greatest height anterior of adductor muscle scars, apex of curvature of anterior and posterior margins below mid-height, dorsal view ovoid, but relatively narrow, with anterior more pointed than posterior. Antenna with very reduced natatory setae, not reaching to end of next segment. Claw G2 of female antenna relatively short, approximately 80% length of claw G1. Seventh limb with relatively long g seta, approximately as long as final segment, and with relatively long, straight h2 seta. Claw Gp of caudal ramus slightly shorter than claw Ga, setae sa and sp approximately equal in length. Lobe b of hemipenes triangular in shape with narrowly rounded apex, lobe a with quadrate end, projecting beyond lobe b.

Description
Carapace (Figures 2C-F, 3A) length 524-536 µm, height 304-320 µm. Right valve overlaps left along all margins. Ventral margin almost straight. Dorsal margin straight, slightly sloping towards posterior. Greatest height anterior of adductor muscle scars. Inner calcified lamella wider anteriorly than posteriorly. Right valve with list on anterior calcified lamella. Dorsal view ovoid, greatest width behind midlength. Anterior more pointed than posterior. Carapace colour chestnut brown. Surface generally smooth, but with small area of very shallow, ill-defined pits in central-ventral area (only observable with SEM). Antennule ( Figure 3B) with seven articulated segments. First segment with one dorsal seta and two long ventral setae. Second segment with tiny Rome organ and one short dorsoapical seta. Third segment with one medium-length dorsoapical seta. Fourth segment with two long dorsoapical setae and two short ventroapical setae. Fifth segment with two long dorsoapical setae, and one short and one long ventroapical seta. Sixth segment with four long apical setae. Seventh segment with three long setae and aesthetasc ya.
Antennal ( Figure 3C) natatory setae on third segment strongly reduced, not reaching to fifth segment. Male antenna with sub-divided fourth segment. Seta z3 very short, claw z2 well-developed, seta z1 medium-length. Claw G1 short, similar in length to z1. Seta G3 very small. Claw Gm short, less than half length of claw GM.
Female antenna ( Figure 3D) with claw G2 approximately 80% length of claw G1. Setae z2 and z3 short to medium-length, seta z1 long, approximately reaching to end of claw G2. Claw Gm longer than in male, approximately 70% length of GM.
Mandible palp ( Figure 4A, B) large with four segments. Alpha seta very short and slender. Beta seta very short and stout, with stiff setules. Final segment supporting three claws and two setae.
Maxillula ( Figure 3E) with two-segmented palp. First segment with three setae on outer apical edge and one seta in sub-apical position near outer edge. Final segment quadrate with three robust setae and three shorter and more slender setae.
Fifth limb male palps ( Figure 3F) asymmetrical. Left palp slightly widens distally with wide, bluntly rounded terminal hook. Right palp with tightly curved, finger-like terminal hook.
Sixth limb ( Figure 4C) five-segmented, first segment with d1 seta. Second segment with long e seta, extending beyond end of third segment. Third segment with f seta reaching to about end of fourth segment. Fourth segment with two g setae, both extending just beyond fifth segment. Fifth segment with h1 and h3 setae of similar length, and with well-developed, robust, long claw h2.
Seventh limb with four segments ( Figure 4D), first segment with d1, d2 and dp setae present. Second segment with e seta reaching beyond mid point of next segment. Third segment with long f seta, extending beyond end of third segment and g seta extending to end of fourth segment. Fifth segment with long, reflexed h3 setae, relatively long h1 and h2 setae.
Caudal ramus ( Figure 4E) relatively robust, claw Gp slightly shorter than Ga. Seta sp almost reaching to base of claw Gp. Seta sa approximately one-third the length of claw Ga.
Hemipenes ( Figure 4F) with strongly rounded outer margin and slightly curved inner margin, lobe a with quadrate shape distally. Lobe b triangular, with rounded apex, not reaching to end of lobe a.

Remarks
Three previously described Cyclocypris species have natatory setae not reaching beyond the claws of the antennae: Cyclocypris breviseptosa (Bronshtein, 1925), C. mediosetosa Meisch, 1987, andC. diebeli Absolon, 1973. Cyclocypris breviseptosa is known from only one site in north-east Russia, near the Arctic Circle (Bronshtein 1988). Compared with C. anacola n. sp., C. breviseptosa has longer natatory setae on the antennae, a wider a-lobe on the hemipenis, and is much more inflated in dorsal view (width/length = 0.71, compared with 0.55 for C. anacola n. sp.). Cyclocypris mediosetosa is known from France and Italy (Meisch 1987;Pieri et al. 2009). The overall carapace shape of C. mediosetosa is similar to that of C. anacola n. sp., although in dorsal view C. mediosetosa is slightly wider (width/length = 0.6), and the carapace has a vertical band of shallow pits mid-length. Additionally, C. mediosetosa has longer natatory setae, a S-shaped h2 seta on the seventh limb (straight with a small hook distally in C. anacola n. sp.) and considerably differently shaped hemipenes. Extant C. diebeli are only known from Hokkaido, Japan, although fossils are known from Europe (Matzke- Karasz et al. 2004). The carapace of C. diebeli is much more globular than that of C. anacola n. sp., has a series of small platelets along the anterior margin of the right valve, and opposite valve overlap (left valve overlaps right). The natatory setae of the antennae are much longer than those of C. anacola n. sp., reaching to almost the ends of the claws, and the hemipenes are shaped differently, especially the outer margins.
The strongly reduced natatory setae on the antennae indicate that this species cannot swim. The presence of an eye and dark coloration of the carapace suggest that this species may not be restricted to subterranean habitats.
Genus Physocypria Vávra, 1897 Physocypria nipponica Okubo, 1990 Remarks Previously this species has been reported from various localities on the Korean Peninsula and Japan (Okubo 1990a(Okubo , 2004Smith and Janz 2008;Chang et al. 2012). Physocypria kraepelini Muller, 1903 has also been reported from Korea (Lee et al. 2000), and as Smith and Janz (2008) noted, the two species may be synonyms, although further work is required to confirm this. During our surveys, this species was recovered from nine localities (1, 3, 4, 6, 7, 10, 26, 28 and 31) from a range of habitats, including marshes, swamps, a lotus pond, irrigation ponds and a cave.
Subfamily PARACYPRIDINAE Sars, 1923 Genus Dolerocypria Tressler, 1937 Dolerocypria mukaishimensis Okubo, 1980 Remarks Dolerocypria mukaishimensis is a relatively common species found in brackish water habitats around Japan (Okubo 1980;Nakao and Tsukagoshi 2002;Smith and Kamiya 2003), Korea (Lee et al. 2000;Karanovic and Lee 2012) and China (Dai et al. 1995). Karanovic and Lee (2012) figured a Korean specimen of D. mukaishimensis with three setae on the first segment of the sixth limb. Japanese specimens have two setae on this segment (Okubo 1980;Nakao and Tsukagoshi 2002), and all Korean material checked by us also has two setae, suggesting that Karanovic and Lee's (2012) specimen is aberrant. This species was found in seven brackish water localities (8,18,19,20,23,27 and 30) during our surveys.

Material examined
Eleven females (including type material) collected from the type locality, 8 September 2013.   Alpha seta of mandibular palp with wide base, tapering distally and sporting one long, fine setule, and beta seta stout with numerous stiff setules. Sixth limb with short d1 seta, much shorter than d2 seta, and long f seta, reaching well beyond end of fifth segment. Caudal ramus with no sa seta, long Ga claw, and very small Gp claw and sp seta; seta sp longer than claw Gp.  Anterior margin slightly more inflated than posterior margin, maximum curvature below mid-height. Ventral margin sinuous. Both valves with well-developed outer lists along ventral margins. Dorsal view egg-shaped with maximum width posterior of mid-length, posterior margin evenly rounded and more inflated than anterior margin; anterior margin slightly angular either side of valve margins. Internally, calcified inner lamella wider anteriorly than posteriorly, and right valve with well-developed groove running near free margin. Septa well developed along anterior margins of both valves. Surface of valves strongly pitted in central area, with shallower and smaller pits towards valve margins. Dorsal areas of valves almost smooth. Colour yellowish with dark green patches ( Figure 7F). Antennule ( Figure 6B) with seven articulated segments. First segment with one dorsal seta and two long ventral setae. Second segment with tiny Rome organ and one short dorsoapical seta. Third segment with one short dorsoapical seta and one short ventroapical seta. Fourth and fifth segments each with two long dorsoapical setae and two short ventroapical setae. Sixth segment with four long and one tiny apical setae. Seventh segment with two long and one medium-length setae, and aesthetasc ya.

Derivation of name
Antennal ( Figure 6C) natatory setae on third segment long, extending to just beyond ends of claws. Shorter seta accompanying long natatory setae relatively very long, extending well beyond end of segment. Claw Gm very slender, approximately 80% length of claw GM. Claw G2 approximately 85% length of claw G1, and with serration more robust than other claws. Seta z3 stout, almost as long as claw G2.
Mandibular palp with four segments ( Figure 6D). Alpha seta of mandibular palp with wide base, tapering distally and sporting one long, fine setule. Beta seta stout with numerous stiff setules ( Figure 6E). Maxillula ( Figure 7A) with two-segmented palp. First segment with four setae on outer apical edge and one seta in sub-apical position near outer edge. Final segment elongate with one robust, claw-like seta and four more slender setae. Third endite with two smooth Zahnborsten.
Fifth limb ( Figure 7B) endite with approximately 12 setae distally, and slender d seta on inner edge. Palp elongate and very lightly sclerotized, terminating with one long and two shorter setae.
Sixth limb ( Figure 7C) five-segmented, first segment with short d1 seta and longer d2 seta. Second segment with long e seta, extending to end of fourth segment. Third segment with long f seta reaching well beyond end of fifth segment. Fourth segment with short g seta, reaching to approximately end of fifth segment. Fifth segment with tiny h3 seta, longer h1 seta and well-developed, robust claw h2.
Seventh limb ( Figure 7D) first segment with d1, d2 and dp setae. Second segment with relatively short e seta. Third segment with short f seta at approximately midlength. Pincer with short h3 seta and short, stout h2 seta.
Caudal ramus ( Figure 7E) with delicate and short ramus. Claw Ga long, more than half length of ramus. Claw Gp very short, shorter than adjacent Sp seta. Sa seta absent.

Remarks
Three previously described species of Cypretta have a similar low lateral view to C. karanovicae n. sp.: C. baylyi McKenzie, 1966, C. lutea McKenzie, 1966and C. patialaensis Battish, 1982. Cypretta baylyi is known from north-western Australia (McKenzie 1966;De Deckker 1981;Bayly 1997) and differs from C. karanovicae n. sp. in that the dorsal margin is more evenly curved, the anterior margin is more inflated and the dorsal view is slightly less globular with maximum width further towards the anterior. Additionally, C. baylyi is strongly pitted over the entire carapace surface and the caudal ramus has a much longer Gp claw compared with C. karanovicae n. sp. Cypretta lutea is another species known from north-western Australia (McKenzie 1966) and in addition to the low lateral view of the carapace, has a similar dorsal view to C. karanovicae n. sp. It differs from C. karanovicae n. sp. in that the surface is smooth with scattered pits, the dorsal margin is more evenly rounded, it lacks green patches, and the Gp claw of the caudal ramus is considerably longer at over half the length of claw Ga. Cypretta patialaensis is an Indian species (Battish 1982), which is distinguished by a noticeable asymmetry in dorsal view. Additionally, the carapace lacks green patches, and the Gp claw of the caudal ramus is much longer than that of C. karanovicae n. sp.
The caudal ramus of C. karanovicae n. sp. is unusual in that seta sp is larger than claw Gp, in contrast to most other species where Gp is larger than sp (some species lack sp). However, even though the taxonomy of the genus relies very heavily on the morphology of the caudal ramus, this appendage is partially reduced in Cypretta species, and thus the lengths of claws and setae could be relatively plastic. Further work is required to determine whether this appendage is a robust taxonomic character for species discrimination in this genus. So far this species is only known from the type locality (locality 26). Gauthier, 1929 ( Figure 5F-J)

Remarks
Adult females collected from Jeju Island showed a large size range from 620 through to 709 μm in length (Appendix 1). The dorsal view was noticeably variable in shape, with a width/length ratio ranging from 0.74 through to 0.81 ( Figure 5I, J), and with the position of maximum width ranging from a position 38 to 43% of the length from the posterior margin (Appendix 1). This large variation may indicate that cryptic species exist within this widespread parthenogenetic form. Cypretta seurati is widespread in circum-tropical regions and warmer areas of temperate zones (Meisch et al. 2007). It has previously been reported from Korea, including Jeju Island, by Kim and Min (1991a). In our surveys, it was collected from 10 localities (4,10,14,17,25,26,28,29,32 and 35) from a wide range of habitats, including marshes, seeps, irrigation ponds, natural pools, and rivers.
In the superfamily Cytheroidea, the presence or absence of tubercles of Cyprideis torosa is ecophenotypically induced (e.g. Keyser 2005), although it is not known what causes differences in surface ornamentation in the Cypridoidea. As the appendages and other carapace features of the Korean specimens are identical to the redescription of B. tuberculata from Thailand, we conclude that the Korean specimens represent a form of B. tuberculata with very weakly developed or absent tubercules.
In Japan, both Strandesia tuberculata and Strandesia decorata (Sars, 1903) have been reported (Okubo 1990b), but later the Japanese specimens were considered to all be S. decorata (Okubo, 2004). However, S. decorata has a smooth carapace (Sars 1903;Savatenalinton and Martens 2010), whereas the Japanese specimens are clearly striated. We consider that the Japanese and Korean specimens are conspecific, and specimens with weak or no tubercles attributed to S. decorata by Okubo (1990bOkubo ( , 2000Okubo ( , 2004 are B. tuberculata. The Thai specimens figured by Savatenalinton and Martens (2009a) also appear to have two weakly developed posterior tubercules in addition to the two anterior tubercles, similar to Strandesia spinulosa Bronshtein in Akatova, 1958. Further investigation is required to determine whether these two species are synonyms.
Bradleytriebella tuberculata is known from India (Hartmann 1964 as S. tuberculata), Thailand (Savatenalinton and Martens 2009a), Japan (Okubo 1990b as S. tuberculata and S. decorata; Okubo 2000 as S. tuberculata and S. decorata; Okubo 2004 as S. decorata), and Taiwan (Yu et al. 2009, as Bradleystrandesia tuberculata, citing grey literature). From Japan and Thailand it is known from rice fields, whereas the Korean specimens were recovered from a streamside seep (locality 17) and an irrigation pond (locality 26).

Remarks
Since Klie's (1932) original description of this large (length approximately 2 mm), conspicuous species from Indonesia, it has only been reported twice more, from India (Victor and Fernando 1979b) and Taiwan (Yu et al. 2009, citing grey literature). Victor and Fernando (1979a) were of the opinion that S. flavescens is a junior synonym of Strandesia odiosa (Moniez 1892), after they redescribed the types of S. odiosa, although this was not followed by later authors (e.g. Savatenalinton and Martens 2010). The slightly lower lateral view of the carapace and the list on the anterior calcified inner lamella of the left valve (marked by black triangle 1 on Figure 9A) of S. flavescens discriminate the two species. Additionally, S. flavescens has a series of septa-like structures in the internal part of the margins of the left valve (marked with black triangle 2 of Figure 9A), which are not mentioned or figured in Victor and Fernando's redescription of S. odiosa. Because Victor and Fernando (1979a) considered the two species as synonyms, is not clear whether the previous Indian report is of S. flavescens or S. odiosa. Only one specimen of this species was collected during our surveys, from a lotus pond (locality 6).

Remarks
Tanycypris alfonsi was described using specimens collected from the Munich Botanical Gardens, Germany (Nagler et al. 2014). The German specimens were collected from containers with hydrophytes in glasshouses of the botanical gardens, together with T. centa, another Korean species, and they are considered to be an artificial introduction, unwittingly transported with plants to the botanical gardens. The Korean specimens were collected from two ponds and are most probably a natural occurrence. Tanycypris pellucida (Klie 1932) has been reported from Japan (Okubo 1972, as Strandesia camaguinensis;, 2004Okubo and Ida 1989), but Chang et al. (2012) noted that the Japanese specimens are different from Klie's original description, and more similar to Tanycypris siamensis Savatenalinton and Martens, 2009a. For this study, the specimen figured by Okubo (2004) (labelled 'Tany 30') was investigated. The specimen lacks the groove along the posterior and anterior margins of the left valve, and so is not T. siamensis, which does have a groove running along these margins (Savatenalinton and Martens 2009a). Okubo's (2004) specimen is, however, very similar to Tanycypris alfonsi, which also lacks the groove along the anterior and posterior margins. The specimen's accompanying appendages are incomplete (missing the antennae and caudal rami) and embedded in an unknown matrix (together with the valves) that makes detailed observation difficult. However, it is probable that the Japanese Tanycypris species is conspecific with the Korean and Germany species. During our surveys, Tanycypris alfonsi was found in two irrigation ponds (localities 5 and 7). Tanycypris centa Chang, Lee andSmith, 2012 Genus Potamocypris Brady, 1870 Potamocypris variegata (Brady and Norman, 1889) ( Figure 8G, H)

Cypridopsis variegata Brady and Norman, 1889
Potamocypris variegata Norman, 1889) nov. comb. Daday 1900 Remarks This species has a wide, probably Holarctic distribution (see review of distribution in Meisch 2000), but this is the first report from north-east Asia. It is often found in stagnant and slow flowing waters with dense vegetation (Meisch 2000). During our surveys, Potamocypris variegata was found at only one locality (locality 35), in the lower reaches of a river. Previously, Kim and Min (1991a) reported Potamocypris mastigophora (Meuthuen, 1910) (as Potamocypris producta (Sars, 1924)) from Jeju Island. Their specimens were 'severely damaged' by formalin, and they noted that they were unable to illustrate their specimens in detail (Kim and Min 1991a). Their species determination therefore remains questionable, but as their specimens have five spine-like setae on the final segment of the maxillula (in contrast to four in P. variegata), they are clearly a different species.

Cypris salina Brady, 1868
Cypris fretensis Robertson, 1870 Cyprinotus inaequivalvis Bronshtein, 1928 Heterocypris salina (Brady, 1868) nov. comb. Klie in Stammer 1932 Remarks Heterocypris salina has a Holarctic distribution often found in fresh to slightly brackish waters (Meisch 2000). Its presence along the coast in Korea is thus not unexpected, but this is the first record from the country. It was found at one locality (locality 1) from a freshwater water rock pool and in a small ditch leading from a cave, both of which were overlooking the sea.
Subfamily DOLEROCYPRIDINAE Triebel, 1961Genus Dolerocypris Kaufmann, 1900Dolerocypris ikeyai Smith and Kamiya, 2006 Remarks This species is currently known from Japan and Korea. It is a typical inhabitant of groundwater discharge at the surface, usually in small springs and seeps with a muddy substrate Smith 2011;Chang et al. 2012;this study). A total of three specimens were found at two localities (localities 2 and 33) in springs and seeps during our surveys. Currently, males are only known from two small Japanese islands Smith 2011); the specimens from Jeju Island are all females, but the three specimens collected are not sufficient in number to determine the reproductive mode of the population.

Dolerocypris sinensis Sars, 1903
Remarks Kim and Min (1991b) previously reported this widespread Eurasian species from Jeju island. A pool below a waterfall, and a swamp (localities 4 and 29) both yielded this species during our surveys.

Remarks
Previously, this widespread Palaearctic species was reported from Korea by Chang et al. (2012). It was found at two localities (localities 13 and 33) during our surveys, in springs and seeps, a typical habitat for this species.

Remarks
This species has previously been reported from the island of Yakushima in Kagoshima Prefecture , and in Shiga Prefecture (Smith 2011), Japan. The significantly reduced natatory setae on the antennae clearly distinguish this species from Stenocypris hislopi, which has previously been reported from Korea (Kim and Min 1991a). The Jeju Island specimens came from a spring (locality 24), a similar habitat to the Japanese specimens (springs and river gravels).

Remarks
Ishizakiella miurensis has previously been reported from brackish habitats along the Pacific and Sea of Japan sides of the island of Honshu, and the western and eastern sides of the island of Kyushu, Japan (Tsukagoshi 1994;Yamaguchi 2000). The specimens from Jeju Island are the first outside of Japan, but occur less than 300 km west of the westernmost locality in Kyushu, and thus are not unexpected. On Jeju Island it was found at two localities (localities 9 and 19), both in the run-off of springs at the coast in brackish water.

Remarks
This species belongs to the stationis group of Limnocythere, characterized by a reduced seventh limb, which is significantly smaller than the sixth limb, and a similar carapace shape (Martens 1990). The lack of post-ventral alae on the carapace indicates that it is not the widespread Limnocythere stationis (Vávra, 1891), which has previously been reported from Korea (Lee et al. 2000). It is also sufficiently different from other species of the group to suggest that it is an undescribed species, but as no males were recovered, it is not described herein. On Jeju Island it was found at two localities (25 and 26), in a marsh and an irrigation pond. Remarks With a height/length ratio of 0.45, and a Gm claw on the antenna that is about 50% the length of claw GM, this species most closely resembles Vestalenula cylindrica, which has previously been reported from Korea (Chang et al. 2012). However, the keel on the right valve is relatively short, at about 18% of the length of the valve ( Figure 10G), more similar to the keel of Vestalenula cornelia (see ). This apparent overlapping of characters of two species could indicate that there are unrecognized cryptic species within the genus, or that these characters are more plastic than previously assumed. Without a detailed statistical analysis of the amount of variation of features within the genus (which requires additional material), this issue cannot be currently resolved. Vestalenula cylindrica was found in one sample during our surveys, collected from a marsh (locality 25).

Remarks
The adult male and two juvenile specimens of Terrestricythere ivanovae recovered were all in a badly preserved state, indicating that they were probably deceased when collected. Although unlikely, we cannot rule out that they may have been transported into the cave by natural or artificial means after death. The superfamily Terrestricytheroidea consists of only five described species, known from the Russian Far East (Schornikov 1969(Schornikov , 1980 the Black Sea (Schornikov and Syrtlanova 2008), the UK (Horne et al. 2004), France (Scharf and Keyser 1991) and Japan (Hiruta et al. 2007). The shape of the Korean adult male specimen's carapace, seventh limb and hemipenis, although poorly preserved, closely match those of T. ivanovae ( Figure 11A-C).
Three previous reports of T. ivanovae exist, from the far-east of Russia (two localities), and France (Schornikov 1969(Schornikov , 1980Scharf and Keyser 1991). The Russian specimens were recovered from amongst small pebbles kept moist by mist, rain and sea spray, and supralittoral salt-tolerant plants and littoral filamentous algae. The French specimens were recovered from a freshwater lake. The Korean specimens were recovered from freshwater pools in two coastal caves (locality 1), which drain into the nearby seashore through a brooklet.

Discussion
Of the six ostracod species previously reported from Jeju Island by Min (1991a, 1994b), two species, namely Cypretta seurati and Dolerocypris sinensis, were also found during our study. This difference is probably a reflection of the different types of habitat targeted during the relevant surveys; with the exception of Potamocypris mastigophora, the species reported by Min (1991a, 1994b) are typical taxa of rice fields, a habitat targeted by them, but not during our surveys.
There are now 28 named species of non-marine ostracods reported from Jeju Island, and the two new species and seven new records for Korea reported herein increase the known Korean non-marine ostracod fauna to about 50 named species/subspecies.
The most diverse ostracod subfamily on Jeju Island is the Cypricercinae, represented by five species. This subfamily is the most diverse of the family and is strongly represented in tropical to subtropical regions, but only Strandesia flavescens was previously known exclusively from tropical zones (Indonesia and possibly India; see above). The other four Cypricercinae species are known from slightly cooler areas, such as the Korean Peninsula, Japan and China.
The presence of a Cyclocypris species on the island is unusual as this genus is typically found in cooler regions of the northern hemisphere. For example, in Japan, Cyclocypris species are currently only known from Hokkaido, which has a much cooler climate compared with the rest of the Japanese archipelago. This may be why Cyclocypris anacola n. sp. was found in cooler cave habitats on Jeju Island and not in surface water bodies. The discovery of a Terrestricythere species on the island is also significant in that this is the first record of the superfamily from a cave, and in a subtropical climate. Previous records are from lakes, marine beaches, and supralittoral zones in temperate or sub-arctic climates. In our study, Terrestricythere ivanovae was found in the same cave system as C. anacola n. sp., which suggests that the caves or connecting groundwater may be a refuge for these two species.
The recovery of two specimens of an undescribed Limnocythere species increases the total of the stationis group to nine. Limnocythere stationis is known across the Palaearctic, including Japan and Korea (Lee et al. 2000;Smith and Janz 2009), L. notodonta Várva, 1906 from Indonesia and the Seychelles (Várva 1906;McKenzie 1971), and L. dorsosicula De Deckker, 1981from Australia (De Deckker 1981. Limnocythere cyphoma Smith and Janz, 2009, L. fude Smith and Janz, 2009, L. kamiyai Smith and Janz, 2009, and L. levigatus Smith and Janz, 2009 are currently only known from Lake Biwa (Smith and Janz 2009), while L. xinanensis Zhao, 1987 has been reported from China (Zhao 1987). Including the record herein of Limnocythere sp., seven of the group inhabit North-East Asia, indicating the group may have originated in this region. The stationis group appears to be phylogenetically distinct within the genus, and a review of Limnocythere would probably conclude that a new genus should be erected to accommodate it.