Atyid shrimps (Crustacea: Decapoda: Caridea) of the Ryukyu Islands, southern Japan, with descriptions of two new species

The freshwater atyid shrimps of Ryukyu Islands, southern Japan, are documented and discussed. A total of 21 species of freshwater shrimps, belonging to seven genera is reported. Two new species are here described and illustrated in detail. Caridina sakishimensis Fujino and Shokita, 1975, is synonymized with Caridina prashadi Tiwari and Pillai, 1971. S.ome previous records are revised, viz. Caridina weberi De Man, 1892a is referred to C. laoagensis Blanco, 1939; Neocaridina brevirostris reported from Ishigaki Island by Kubo (1941) is most probably an undescribed species. Caridina hainanensis Liang and Yan, 1983, from China and Caridina blancoi Chace, 1997, from Philippines are also synonymized with Caridina propinqua in the present study.


Introduction
Although the freshwater shrimp fauna of the Ryukyu Islands has been relatively well studied in recent decades Kubo 1938Kubo , 1941Fujino and Shokita 1975;Shokita 1975Shokita , 1979Shokita , 1982Shokita , 1990Shokita , 1996Shokita , 1997Shokita , 2002Shokita , 2003Nishijima 1976, 1977;Suzuki 1980;Hayashi 1989a-d;Naruse et al. 2003Naruse et al. , 2006, no taxonomic review has been carried out. The present study serves to revise the taxonomy of the freshwater shrimp of the family Atyidae of the Ryukyu Islands. It is mainly based on a recent joint investigation by the National University of Singapore and the University of the Ryukyus. Previous collections kept in the National Museum of Natural History, Smithsonian Institution, Washington, DC (USNM); Senckenberg Museum, Frankfurt; Germany (SMF); National Science Museum, Tokyo, Japan (NSMT); the Zoological Reference Collection, Raffles Museum of Biodiversity Research, National University of Singapore, Singapore (ZRC); National Museum of Marine Biology and Aquarium,

Description
Rostrum ( Figures 1A and 3A) reaching to or slightly beyond end of scaphocerite, dorsal margin nearly horizontal, or slightly sigmoid, armed with 16-25 (mode 17-24) teeth throughout dorsal margin, two or three of them situated on carapace posterior to orbital margin, armed ventrally with one to six (mode one to three) teeth. Antennal spine slightly lower than inferior orbital angle; pterygostomian margin subrectangular. Sixth abdominal somite 0.65 times length of carapace, 1.6 times as long as fifth somite, subequal to length of telson. Telson ( Figure 1B,C) 3.2 times as long as wide, not terminating in a posteromedian projection, with two pairs of dorsal spinules and one pair of dorsolateral spinules; dorsal pairs situated near edges; distal end broadly rounded, with about 11 setae, lateral pair slightly longer than intermediates. Preanal ( Figure 1J) carina with a spine.
Eyes well developed, anterior end reaching to 0.8 times length of basal segment of antennular peduncle. Antennular peduncle 0.70 times as long as carapace; basal segment of antennular peduncle distinctly longer than sum of second and third segment lengths, anterolateral angle reaching 0.30 times length of the second segment, second segment distinctly longer than third segment. Stylocerite reaching to 0.7 times length of second segment of antennular peduncle. Scaphocerite ( Figure 1D) 3.0 times as long as wide.
Incisor process of mandible ( Figure 1E) ending in irregular teeth, molar process truncated. Lower lacinia of maxillula ( Figure 1F) broadly rounded, upper lacinia elongate, with a number of distinct teeth on inner margin, palp slender. Upper endites of maxilla ( Figure 1G) subdivided, palp short, scaphognathite tapering posteriorly with numerous long, curved setae at posterior end. Palp of first maxilliped ( Figure 1H) ending in a fingerlike projection. Second maxilliped ( Figure 1I) typical. Third maxilliped ( Figure 2A) reaching to end of antennular peduncle, with ultimate segment slightly shorter than penultimate segment.

Diagnosis
Rostrum short, not reaching beyond end of eyestalk; unarmed. Antennal spine fused fully with inferior orbital angle. Pterygostomian margin broadly rounded. Telson not terminating in a projection, with only two pairs of dorsal spinules on distal two-thirds of telson; with two pairs of distal spines, lateral pair of distal spines distinctly longer than intermediates. Antennular peduncle 0.55 times as long as carapace, stylocerite not reaching to end of basal segment of antennular peduncle. Epipods on first three pereiopods. Merus of first pereiopod as long as ischium; carpus of first pereiopod deeply excavated, subequal to chela in length, 3.3 times as long as high, chela 2.3 times as long as broad, fingers distinctly longer than palm. Merus of second pereiopod as long as ischium; carpus of second pereiopod excavated anteriorly, very slender, seven times as long as high, more than twice longer than chela; chela 2.5 times as long as broad, fingers 1.6 times as long as palm. Propodus of third pereiopod three times as long as dactylus, dactylus 2.5 times as long as wide, with eight spines on flexor margin. Propodus of fifth pereiopods three times as long as dactylus, dactylus 3.5 times as long as broad, with 18-19 spinules on flexor margin. Endopod of male first pleopod subrectangular, no appendix interna, slightly shorter than exopod. Appendix masculina of male second pleopod slender. Uropodal diaeresis with four movable spinules.

Remarks
Halocaridinides Fujino and Shokita 1975, was originally established as a subgenus of Halocaridina. Palauatya was established based on Palau material by Hart (1980). Based on a collection from Palau, Holthuis (1982) synonymized Palauatya with Halocaridinides and raised the latter to full generic rank. Halocaridinides trigonophthalma has been found from Okinawa Island, and Hatoma Island of the Ryukyu Islands (Fujiino and Shokita 1975;Shokita 1975Shokita , 1979Naruse et al. 2003), Palau Islands (Hart 1980;Holthuis 1982) and Guam (Maciolek 1983). Gordon (1968, in Gordon andMonod 1968) described a new species from a subterranean lake in Kufile, Zanzibar, and doubtfully placed it in the genus Parisia Holthuis 1956. Gurney (1984 moved it to Halocaridinides and redescribed it in detail as H. fowleri after re-examining the types. Halocaridinides trigonophthalma could be easily distinguished from H. fowleri by the relative position of the distal end of the antennal carpus (reaching as far as the distal end of the antennular peduncle in H. trigonophthalma vs. reaching as far as the distal end of the antennal scale in H. fowleri). Naruse et al. (2003) used the relative length of the exopod of the third pereiopod against the endopod as one of two characters to differentiate H. trigonophthalma from H. fowleri. However this character is too slight to separate two species (see Hart 1980, Fig. 15;Gurney 1984, Fig. 2B). The disjunct localities in the West Pacific may reflect a possible passive dispersal path by ocean current as suggested by Smith and William (1981) and Maciolek (1983).

Distribution
Known from the Ryukyu Islands, Japan, Palau, and Guam.

Distribution
West Pacific.

Habitat
Lower reaches of rivers and streams which discharge to the sea.

Remarks
Compared to the material of Chace (1983), the number of ventral rostral teeth for this species is more variable in our specimens. It ranges from one to seven. Atyopsis spinipes occurs from Philippines and eastern Lesser Sunda Islands (ca.120u009E) northwards to Taiwan and as far as Tokuno-shima in the Ryukyus, and eastwards as far as Samoa (Chace 1983).

Remarks
This species was recently reported by Shokita (2003). The single specimen on which Shokita's (2003) record was based could not be located in the present study.

Distribution
Indo-West Pacific.

Habitat
Lower reaches of rivers and streams which discharge to the sea.

Remarks
Cai et al. (2006) recently designated a neotype for C. leucosticta Stimpson, 1860 and redescribed it in detail.

Distribution
Caridina leucostica has only been reported with certainty from Japan thus far

Habitat
Lower reaches of rivers and streams which discharge to the sea.

Remarks
Cai and  recently discussed the taxonomy of Caridina serratirostris and C. celebensis, and pointed out that ''In Ryukyus, specimens with short rostrum are mostly of C. celebensis, while those with long rostrum, almost all having arthrobranch on the first pereiopod, are of C. serratirostris.'' Distribution Japan, Philippines, Fiji, Malaysia, Indonesia and Madagascar. Habitat Lower reaches of rivers and streams which discharge to the sea.

Remarks
Caridina celebensis was recently reviewed by . It is characterised by the absence of an arthrobranch on the base of the first pereiopod. Caridina celebensis is distributed from Sulawesi, Indonesia to Honshu, Japan.
Sixth abdominal somite 0.40 times length of carapace, 1.3 times as long as fifth somite, shorter than telson. Telson ( Figure 5C) 2.5 times as long as wide, terminating in a projection, with five pairs of dorsal spinules and one pair of dorsolateral spinules; distal end with two pairs of spines and three to four pairs of plumose setae, lateral pair of spines distinctly longer than sublateral pair, intermediate pairs of setae distinctly longer than later spines, distal margin broadly rounded. Preanal carina high, without spine ( Figure 5B).
Eyes well developed, anterior end reaching to 0.7 times length of basal segment of antennular peduncle. Antennular peduncle 0.52 times as long as carapace; basal segment of antennular peduncle longer than sum of second and third segment lengths, anterolateral angle reaching 0.20 times length of the second segment, second segment distinctly longer than third segment. Stylocerite ( Figure 5D) reaching 0.8 length of basal segment of antennular peduncle. Scaphocerite 2.6 times as long as wide.  Incisor process of mandible ending in irregular teeth, molar process truncated. Lower lacinia of maxillula broadly rounded, subtriangular, upper lacinia elongate, with a number of distinct teeth on inner margin, palp slender. Upper endites of maxilla subdivided, palp short, scaphognathite tapering posteriorly with numerous long, curved setae at posterior end. Palp of first maxilliped ending in a finger-like projection. Second maxilliped typical, arthrobranch well developed. Third maxilliped reaching to end of antennular peduncle, with ultimate segment shorter than penultimate segment.
Epipods well developed on first four pereiopods. First pereiopod ( Figure 5E) reaching to distal end of basal segment of antennular peduncle; merus 2.1 times as long as broad, as long as, or slightly longer than carpus; carpus excavated anteriorly, shorter than chela, 1.3 times as long as high; chela 2.4 times as long as broad; fingers subequal to length of palm. Second pereiopod ( Figure 5F) reaching to end of second segment of antennular peduncle; merus slightly shorter than carpus, 4.3 times as long as broad; carpus slightly longer than chela, 4.3 times as long as high; chela 2.9 times as long as broad; fingers 1.6 times as long as palm. Third pereiopod ( Figure 5G, H) reaching to end of scaphocerite, propodus 8.3 times as long as broad, 3.7 times as long as dactylus; dactylus 2.2 times as long as wide (spines included), terminating in one stout claw, with five accessory spines on flexor margin. Fifth pereiopod ( Figure 5I, J) reaching to end of antennular peduncle, propodus 9.2 times as long as broad, 3.3 times as long as dactylus, dactylus 3.1 times as long as wide (spinules included), terminating in one elongated claw, with 28-42 spinules on flexor margin.
Endopod of male first pleopod sub-triangular, reaching to one-thirds length of exopod, appendix interna reaching beyond distal end of endopod by most of its length. Appendix masculina of male second pleopod reaching to two-thirds length of exopod.

Habitat
Rivers and streams which discharge to the sea.

Remarks
Chace (1997) recently redescribed this species on the basis of specimens from Philippines. He (Chace 1997, p 13) also commented that it ''…is possible that C. laoagensis will eventually fall into synonymy with the variable C. weberi from Indonesia,…'' According to an on-going revision by one of the authors (YC), most of the subspecies of C. weberi, are in fact, distinct species. Among all the allied species, C. laoagensis is most similar to C. weberi De Man, 1908a by the form of the rostrum, which is straight, pointed and crested at the base of the rostrum; the spines and setae on the distal margin of the telson (the longer setae arranged between two pairs of strong spines, of which, the sublateral pair shorter than the lateral pair vs. the longer setae arranged between one pair of strong spines).
Caridina laoagesis appears to be rare in Ryukyu Islands. It has previously been reported from Tabaru River of Yonaguni Island, Nagura and Miyara Rivers of Ishigaki Island, and Shigema, Yona and Manna Rivers of Okinawa Island by Shokita (1979Shokita ( , p 2003 as Caridina weberi.

Diagnosis
Rostrum straight or slightly upturned, reaching to end of second segment of antennular peduncle, or to end of scaphocerite. Rostrum with teeth throughout its dorsal margin, rostral formula 9-14+15-24/9-23. Antennal spine prominent, situated lower than suborbital angle; pterygostomian margin rounded; eyes strongly reduced. Preanal carina with spine. Telson with five pairs of dorsal spines, small posteromedial projection, lateral pair of spines longer than or as long as intermediate pairs of setae. Antennular peduncle 0.5-0.6 times as long as carapace. Stylocerite reaching to end of basal segment of antennular peduncle, or slightly beyond it. Scaphocerite 3.1 times as long as wide.
First pereiopod with ischium much shorter than merus, carpus 1.0-1.5 times as long as chela, 4.2 times as long as high, chela 2.0-3.0 times as long as broad, finger distinctly longer than palm. Second pereiopod with ischium much shorter than merus, carpus 1.5-2.0 times as long as chela, 8-12 times as long as high, chela 2.4-4.0 times as long as broad, fingers 1.5-2.0 times as long as palm. Third pereiopod with propodus not enlarged, its length 4.0-5.0 times as long as dactylus; dactylus ending in two claws, with two to four spines on flexor margin. Fifth pereiopod with propodus 5.0-6.5 times as long as dactylus, dactylus ending in one claw, with 13-17 spinules on flexor margin. Endopod of male first pleopod sub-triangular, no appendix interna. Uropodal diaeresis with 11-13 spinules.

Habitat
Subterranean water.

Remarks
The forms of the rostrum, the first two pereiopods and telson are much more variable than in the original description by Fujino and Shokita (1975). Holthuis (1978) described Caridina troglodytes, on the basis of four incomplete specimens from Danmin Cave near Konogusgus, New Ireland. Caridina troglodytes is very similar to C. rubella, most of its characters fall within the range of variation of C. rubella, except for the smaller number of ventral rostral teeth (2-8 vs. 9-23) and the fewer spinules on the dactylus of the fifth pereiopods (6 vs. 13-15). As the ventral rostral teeth are quite variable in both species and  the supposed fifth pereiopod is unattached, and thus could be the fourth pereiopod instead, the identity of Holthuis' species need more specimens for it to be ascertained. Shokita (1979) reported it from two more locations in southern Japan, one from subterranean water of Shiokawa River, Okinawa Island, Ryukyus, and the other from Suirendo Cave, Okinoerabu Island, Ryukyu Islands. Cai and Anker (2004) reported the occurrence of Caridina rubella from Palawan Island, the Philippines.

Diagnosis
Rostrum straight, reaching near to middle of second segment of antennular peduncle. Rostral formula 1-6/3-6. Suborbital angle acute, fused with antennal spines; pterygostomian margin rectangular. Preanal carina with no spine. Telson with small posteromedial projection, lateral pair of spines shorter than intermediate pairs. Antennular peduncle 0.6 times as long as carapace. Stylocerite reaching 0.8 times length of basal segment of antennular peduncle. Scaphocerite 2.9 times as long as wide. First pereiopod with carpus 1.1-1.3 times as long as high, chela 2.0 times as long as broad, finger distinctly shorter than palm. Second pereiopod with carpus 4.5 times as long as high, chela 2.6 times as long as broad, fingers 1.5 times as long as palm. Third pereiopod with propodus 4.0-4.8 times as long as dactylus; dactylus ending in two claws, with two to four spines on flexor margin. Fifth pereiopod with propodus 4.5-5.0 times as long as dactylus, dactylus ending in one claw, with 29 spinules on flexor margin. Endopod of male first pleopod sub-triangular, with appendix interna. Uropodal diaeresis with 21-22 spinules.

Habitat
Mountain streams or rivers.

Remarks
Tiwari and Pillai (1971) described a new species, Caridina prashadi, from the southern Andaman Islands. Fujino and Shokita (1975) did not compare it with C. prashadi when they described C. sakishimensis from Southern Ryukyus. It was subsequently recorded from Kume Island of the northern Ryukyus and Okinoerabu Island of the central Ryukyus (Shokita 1979;Suzuki and Sato 1994). Examination of one fresh collection from the Andaman Islands (2 females, cl 4.0-4.1 mm, 1 ovigerous female, ZRC, Mount Harriet National Park, south Andaman Islands, India, coll. Indranei Das, 20 August 1997) and re-examination of the types in the Ryukyu University, and the examination of fresh material from Iriomote Island indicated that C. sakishimensis is, in fact, identical with C. prashadi. The record of C. rapaensis by Shokita (2003) was based on these specimens and should thus be reassigned here.

Habitat
Lower reaches of rivers or mountain streams which discharge to the sea. Commonly found in mangrove creeks.

Remarks
Liang and Yan (1983) described Caridina hainanensis on the basis of specimens from Hainan Island. Their species has the same typical characteristics as C. propinqua, namely the form of the rostrum and the telson, the form of various pereiopods, especially the third, which has a very small number of spines (one to three in C. hainanensis vs. one to four in C. propinqua) on the flexor margin of the dactylus, the identical form of the endopod of male first pleopod. Re-examination of the types indicated that C. hainanensis should be regarded as a junior synonym of C. propinqua. Chace (1997) proposed a new species, based on a single specimen. He commented that ''(t)he proposal of a new species, based on a single specimen in a genus that is noteworthy for its variable species, may be questionable, but it seems desirable to call attention to a taxon that apparently differs from all others known in a combination of characters; the form and dentition of the rostrum and telson; the prominence of the suborbital angle; and the form of the chelae and carpi of two anterior pereiopods and of the dactyls of the third and fourth pereiopods.'' Re-examination of the holotype confirms that it is identical with C. propinqua.
Egg size of this species is quite variable. It is 0.39-0.4560.24-0.27 mm in specimens from Hainan (Liang and Yan 1983), 0.5460.36 mm in populations from Malaysia (Johnson 1961) and 0.38-0.4860.25-0.30 mm in the present specimens from the Ryukyus. Kemp (1918) reported C. propinqua from southern Thailand. The identity of his species is doubtful as it had an egg size of 0.64-0.7060.39-0.44 mm, which is much larger than in specimens from elsewhere. This record has recently been reported by Shokita (2003). Previously, Caridina propinqua has been reported from Sri Lanka (De Silva 1982), India (De Man 1908b;Kemp 1915), Malaysia (Johnson 1961;Ng and Choy 1990), southern China (Liang and Yan 1983) and the Philippines (Chace 1997).

Distribution
Sri Lanka, India, Malay Peninsula, Philippines, and China.

Description
Rostrum ( Figure 12A) short, straight, reaching near end of second segment of antennular peduncle; dorsal margin with 12 teeth, three of them on carapace, ventral margin with five very small teeth; inferior orbital angle of carapace fused with antennal spine, sharp and long; pterygostomial angle rectangular. Sixth abdominal somite 0.50 times as long as carapace, 1.6 times as long as fifth somite, slightly shorter than telson. Telson terminating in median projection; five pairs of dorsal spinules, one pair of dorsolateral spines near distal end, four pairs of spines on distal margin, lateral pair shortest, sublateral pair longest; preanal carina high, with a small spine. Scaphocerite 2.8 times as long as wide. Eyestalk short, eye with an undeveloped cornea. Antennular peduncle stout, 0.5 times as long as carapace; stylocerite reaching slightly beyond end of basal segment of antennular peduncle.
Third maxilliped reaching to end of third segment of antennular peduncle, with ultimate segment shorter than penultimate segment. Epipods on first four pereiopods. First pereiopod ( Figure 12C) stout, reaching to middle of second segment of antennular peduncle, ischium much shorter than merus, merus 2.0 times as long as broad, as long as carpus; carpus excavated anteriorly, shorter than chela, 1.2 times as long as high; chela 1.9 times as long as broad; fingers 0.6 times as long as palm. Second pereiopod ( Figure 12D) reaching end of second segment of antennular peduncle, ischium much shorter than merus, merus slightly longer than carpus, 5.4 times as long as broad; carpus 1.3 times as long as chela, 5.0 times as long as high; chela 2.4 times as long as broad; fingers 1.3 times as long as palm. Third pereiopod ( Figure 12E, F) reaching end of third segment of antennular peduncle, propodus normal shape, distinctly shorter than merus, 9.0 times as long as broad, 4.5 times as long as dactylus; dactylus ending in two strong claws; 2.6 times as long as wide (spines included), with five accessory spines on flexor margin. Fifth pereiopod ( Figure 12G, H) reaching to end of basal segment of antennular peduncle, propodus distinctly longer than merus, 11 times as long as broad, 4.7 times as long as dactylus; dactylus 2.6 times as long as wide, ending in two large claws, with 26 spinules on its flexor margin. Uropodal diaeresis with 17 spinules.

Etymology
The new species is named after the type locality, Okinawa Island, Ryukyus, used as a noun in apposition.

Remarks
With respect to the rostral formula, and the long stylocerite, Caridina okinawa, new species, is very different from all the epigean Caridina species from the Ryukyus. It is however, most similar to C. cantonensis Yu, 1938 (cf. Cai and from southern China. It could be distinguished by the shorter stylocerite (reaches to the end of basal segment of antennular peduncle vs. distinctly beyond); the less developed eyes (vs. well developed in C. cantonensis); the shorter finger of the first pereiopod (0.6 times as long as palm vs. as long as palm).

Distribution
Known only from the type locality, Okinawa Island, Ryukyu Islands.

Description
Rostrum ( Figures 13A and 14A) short, straight, with a pointed end, reaching middle of second segment of antennular peduncle; dorsal margin with 12-15 large teeth, two to three of them on carapace, ventral margin with three to five very small teeth; inferior orbital angle of carapace fused with antennal spine, sharp, long; pterygostomial angle broadly rounded.
Sixth abdominal somite 0.41 times as long as carapace, 1.2 times as long as fifth somite, slightly shorter than telson. Telson ( Figure 13B, C) 2.8 times as long as wide, terminating in median projection; five to seven pairs of dorsal spinules, one pair of dorsolateral spines near distal end, one pair of spines and three pairs of subequal spiniform setae on distal margin; lateral spine slightly shorter than intermediate pairs of setae. Preanal carina high, without spine.  Eyes ( Figures 13A and 14A) well developed, reaching to 0.8 times length of basal segment of antennular peduncle. Antennular peduncle stout, 0.6 times as long as carapace; basal segment of antennular peduncle longer than sum of second and third segment lengths of antennular peduncle, anterolateral angle reaching 0.2 times length of second segment; second segment slightly longer than third. Stylocerite reaching 0.9 times length of basal segment of antennular peduncle. Scaphocerite ( Figure 14B) 2.8 times as long as wide.
Incisor process of mandible ( Figure 13D) ending in irregular teeth, molar process truncated. Lower lacinia of maxillula ( Figure 13E) broadly rounded, subtriangular, upper lacinia elongate, with a number of distinct teeth on inner margin, palp slender. Upper endites of maxilla ( Figure 13F) subdivided, palp short, scaphognathite tapering posteriorly with numerous long, curved setae at posterior end. Palp of first maxilliped ( Figure 13G) terminating in broad triangular end. Second maxilliped ( Figure 13H) typical, arthrobranch well developed. Third maxilliped ( Figure 13I) reaching to end of antennular peduncle, with ultimate segment shorter than penultimate segment.
Epipods on first four pereiopods. First pereiopod ( Figure 14C) stout, reaching to end of basal segment of antennular peduncle, merus 2.0 times as long as broad, slightly longer than carpus; carpus strongly excavated anteriorly, shorter than chela, 1.2 times as long as high; chela 2.0 times as long as broad; fingers as long as palm. Second pereiopod ( Figure 14D) reaching end of second segment of antennular peduncle, merus slightly longer than carpus, 4.4 times as long as broad; carpus slightly longer than chela, 3.8 times as long as high; chela 2.5 times as long as broad; fingers 1.7 times as long as palm. Third pereiopod ( Figure 14E, F) reaching end of third segment of antennular peduncle, propodus distinctly shorter than merus, 8.5 times as long as broad, 4.3 times as long as dactylus; dactylus ending in two strong claws; 2.5 times as long as wide (spines included), with three accessory spines on flexor margin. Fifth pereiopod ( Figure 14G, H) reaching to end of basal segment of antennular peduncle, propodus distinctly longer than merus, 11 times as long as broad, 4.7 times as long as dactylus; dactylus 2.4 times as long as wide, ending in two large claws, with 26 spinules on flexor margin.

Habitat
The holotype specimen was caught from a fast flowing stream, hiding under vegetation at the edge of the stream. The collection site is about 200 m from the sea.

Etymology
The name is derived from Latin, macro, large, and dentata, toothed, alluding to the large teeth on the dorsal margin of the rostrum.

Remarks
With regard to the form of the rostrum, the large number of uropodal spinules and the form of various pereiopods, Caridina macrodentata should be referred to the C. weberi species group. In the group, it is most similar to C. weberi papuana, which, however, can be separated from C. weberi papuana by its longer rostrum, the larger rostral teeth and the biunguiculate dactylus of the fifth pereiopod.
The new species is also close to C. okinawa, new species. The rostral formula, the form of the preanal carina, and pereiopods are shared only by these two species in the Ryukyus. Caridina okinawa was found from subterranean water in Okinawa, central Ryukyus, while C. macrodentata was caught from epigean waters in Iriomote, southern Ryukyus. Caridina macrodentata differs from C. okinawa by its well developed eyes, larger teeth on the dorsal margin of the rostrum, the relatively broad scaphocerite (2.5 time as long as wide vs. 2.8 times); the longer fingers of the first pereiopod (as long as palm vs. 0.6 times), the longer fingers of the second pereiopod (1.7 times as long as palm vs. 1.3 times) and the shorter stylocerite (does not reach the end of basal segment of antennular peduncle vs. reaching). Cai and Ng (2001) doubtfully referred a damaged specimen from Halmahera, Indonesia, to Caridina pareparensis De Man, 1892a. According to the available characters, especially the rostrum and the first pereiopod, it most probably belongs to the present new species, and is formally referred to it here.
Sixth abdominal somite 0.49 times length of carapace, 1.4 times as long as fifth somite, as long as telson. Telson ( Figure 16A, B) 3.0 times as long as wide, terminating in a projection, with five to six pairs of dorsal spinules and one pair of dorsolateral spinules; distal end with about four to five pairs of spines, lateral pair as long as or slightly longer than intermediate pairs, sublateral pair shortest. Preanal carina ( Figure 20K) without spine.
Eyes well developed, anterior end reaching to 0.8 times length of basal segment of antennular peduncle. Antennular peduncle 0.57-0.63 times as long as carapace; basal segment of antennular peduncle longer than sum of second and third segment lengths,   anterolateral angle reaching 0.25 times length of the second segment, second segment distinctly longer than third segment. Stylocerite reaching to 0.85-0.9 length of basal segment of antennular peduncle. Scaphocerite ( Figure 15B) 2.8 times as long as wide.
Incisor process of mandible ( Figure 15C) ending in irregular teeth, molar process truncated. Lower lacinia of maxillula ( Figure 15D) broadly rounded, upper lacinia elongate, with a number of distinct teeth on inner margin, palp slender. Upper endites of maxilla ( Figure 15E) subdivided, palp short, scaphognathite tapering posteriorly with numerous long, curved setae at posterior end. End of palp of first maxilliped ( Figure 15F) truncate. Podobranch of second maxilliped ( Figure 15G) well developed. Third maxilliped ( Figure 15H) reaching to end of scaphocerite, with ultimate segment as long as or slightly shorter than penultimate segment.
Epipods present on first four pereiopods. First pereiopod ( Figures 16C and 17B) reaching to distal end of basal segment of antennular peduncle; merus 2.6-2.7 times as long as broad, slightly longer than carpus; carpus excavated anteriorly, shorter than chela, 1.6-1.8 times as long as high; chela 2.1-2.3 times as long as broad; fingers 1.1-1.4 times as long as palm. Second pereiopod (Figures 16D and 17C) reaching to end of antennular peduncle; merus slightly shorter than carpus, 5.1-5.3 times as long as broad; carpus 1.15-1.25 times as long as chela, 5.0-5.1 times as long as high; chela 2.6-2.9 times as long as broad; fingers 1.4-1.7 times as long as palm. Third pereiopod (Figures 16E,F and 17D,E) reaching to end of scaphocerite, propodus incurved strongly in male but straight in female, 7.4-8.4 times as long as broad, 3.4-4.2 times as long as dactylus; dactylus 2.0 times as long as wide in male and 2.6 times in female (spines included), terminating in two claws, with three to four accessory spines on flexor margin. Fifth pereiopod ( Figures 16G, H and 17F, G) reaching beyond end of basal segment of antennular peduncle, propodus 8.6-10 times as long as broad, 3.1-3.3 times as long as dactylus, dactylus 3.0-3.3 times as long as wide (spinules included), terminating in one claw, with 25-46 spinules on flexor margin.
Endopod of male first pleopod ( Figure 16I) inflated at distal three-quarters into palmshape, with numerous tiny spinules on distal portion of dorsal surface; appendix interna at base of endopod, small, elongate, or reduced, 1.5 times as long as wide, 0.7 times length of exopod. Appendix masculina of male second pleopod ( Figure 16J) cylindrical, reaching to half length of endopod, armed with numerous stout spines on surface, with appendix interna reaching to distal quarter of appendix masculina or near its distal end.

Habitat
Mountain streams.

Remarks
Fujino and Shokita (1975) described it as a subspecies of Caridina denticulata (De Haan, 1849), on the basis of specimens from Ishigaki Island. Shokita (1979) raised it to a full species, Neocaridina ishigakiensis. In his revision of the genus Neocaridina, Cai (1996) treated it as a subspecies of N. palmata (Shen, 1948), as the sexual appendages are very similar to the nominal subspecies. Apart from the differences in the rostrum, the appendix interna of the male first pleopod is also shorter than that of N. palmata. While N. ishigakiensis is morphologically closer to N. palmata than N. denticulata (cf. Cai 1996), we nevertheless follow Shokita (1979) in regarding it as a distinct species as recent investigations have shown that it is restricted to Ishigaki Island, and there are no intermediate forms, and no range overlap in the distributions of N. ishigakiensis and N. palmata. Liang (2004) recently reported the occurrence of Neocaridina denticulata ishigakiensis from Wenling, Zhejiang Province. His drawing (Liang 2004, fig. 42) shows that sexual appendages of his specimens are much more like those of Neocaridina sinensis than N. ishigakiensis.

Distribution
Several localities on Ishigaki Island.

Remarks
This species has been described in detail, with comparisons being made against several congeners (see Naruse et al. 2006).

Distribution
Known only from the type locality, Iriomote Island.

Material examined
None.

Habitat
Mountain stream.

Remarks
Stimpson (1860) briefly described C. brevirostris from Loo Choo (Okinawa) Island. Kubo (1941) redescribed it based on specimens from Ishigaki Island, and transferred it to the genus Neocaridina. , however, synonymized C. brevirostris with Atyoida pilipes as no Neocaridina species have been found from Okinawa Island and the only form that fits well with Stimpson's description of C. brevirostris around Okinawa Island is Atyoida pilipes (Newport, 1847). Therefore, Kubo's (1941) N. brevirostris is in fact, an unnamed species. This uncertain species is morphologically very close to the short rostrum form of the Neocaridina iriomotensis, new species, but could be distinguished by the shorter rostrum (not reaching to the end of the basal segment of antennular peduncle vs. reaches to or slightly beyond); the pterygostomian angle rounded (vs. with small spine); the stout carapace (1.2 vs. 1.5 times as long as high) and the large egg size (1.560.9 vs. 1.00-1.2060.6-0.8 mm).