A revision of the Caridina gracilirostris De Man, 1892, species group, with descriptions of two new taxa (Decapoda; Caridea; Atyidae)

Re‐examination of the syntypes of Caridina gracilirostris De Man, 1892, shows that the type series is composed of three species. These three species are similar in the form of the rostrum, but can be differentiated easily by a combination of rostral formula and sexual appendages. To stabilize the taxonomic status of these species, a lectotype for C. gracilirostris is selected. A lectotype for Caridina appendiculata Jalihal and Shenoy, 1998, is also designated from among the remaining syntypes of C. gracilirostris. A new species, C. neglecta, is described. Caridina gracilirostris and C. gracilima Lanchester, 1901, are redescribed and figured, and C. appendiculata is transferred to the C. nilotica species group. A new species group is also recognized for C. gracilirostris, C. neglecta, C. gracilima, and a new species, C. longifrons. The C. gracilirostris species group is defined here as taxa possessing a rostrum with subapical teeth, fewer than 10 dorsal teeth, and without any postorbital teeth.


Introduction
When De Man (1892) described Caridina gracilirostris, he noted that there were two forms of pereiopod carpus in his material: a short carpus form from Sulawesi, and a long carpus form from Flores. Tiwari and Pillai (1971) also reported both forms from different parts of the Andaman Islands. Jalihal and Shenoy (1998, p 128), in an abstract, stated that for C. gracilirostris De Man, 1892, ''(I)ts syntype material is actually an assemblage of three taxonomic forms…''. This is something we have also independently observed for the material of ''Caridina gracilirostris'' that we have examined for many years. We have also noted that these three forms also differ from each other in the structure of their sexual appendages. Interestingly, a re-examination of the syntypes of C. gracilirostris shows the type series actually contains representatives of all three forms. In the present study, the taxonomy of C. gracilirostris is revised and clarified. A species group is established for these

Description
Rostrum ending in bifid tip, reaching far beyond distal end of scaphocerite, 1.5-2.0 times as long as carapace, strongly upturned, armed with three to nine dorsal teeth on posterior half, 28-36 teeth throughout ventral margin; antennal spine short, situated below inferior orbital angle; pterygostomian margin sub-rectangular.
Sixth abdominal somite 0.8 times as long as carapace, 2.0 times as long as fifth somite, as long as telson. Telson very slender, 4.8 times as long as wide, with four pairs of dorsal spinules and one pair of dorsolateral spinules; distal spines very stout, lateral pair distinctly longer than intermediate spines; apparently lacking posteromedian projection. Preanal carina with a spine.
Eyes well developed, anterior end reaching to 0.8 times length of basal segment of antennular peduncle. Antennular peduncle 0.8 times as long as carapace; basal segment longer than sum of second and third segment lengths, anterolateral angle pointed, reaching to 0.4 times length of second segment, second segment distinctly longer than third segment. Stylocerite reaching to 0.8-0.9 times length of basal segment of antennular peduncle. Scaphocerite 4.1 times as long as wide.
Incisor process of mandible ending in a row of small teeth, molar process truncate. Lower lacinia of maxillula broadly rounded, upper lacinia elongate, with distinct teeth on inner margin, palp slender. Upper endites of maxilla subdivided, palp short, scaphognathite tapering posteriorly with some long, curved setae at posterior end. Palp of first maxilliped ending in broad triangular structure. Second maxilliped typical of genus. Third maxilliped reaching to end of second segment of antennular peduncle, with ultimate segment distinctly shorter than penultimate segment.
Epipods on first four pereiopods. First pereiopod not reaching beyond end of eye stalk; merus as long as carpus, 2.5 times as long as wide, carpus 1.7 times as long as high; chela twice as long as broad, finger as long as or slightly longer than palm. Second pereiopod reaching beyond end of basal segment of antennular peduncle, merus shorter than carpus, 3.8 times as long as broad; carpus 1.2 times as long as chela, 4.0 times as long as high; chela 2.2 times as long as broad; fingers 1.4 times as long as palm. Third pereiopod reaching to end of antennular peduncle, with propodus 13 times as long as wide, 4.0 times as long as dactylus; dactylus 3.2 times as long as wide (spines included), with eight spines on flexor margin. Fifth pereiopod reaching to end of basal segment of antennular peduncle, with propodus 12 times as long as wide, 3.8 times as long as dactylus; dactylus 3.7 times as long as wide, with 37 spinules on flexor margin.
Eggs 0.460.25 mm in diameter.

Habitat
Lower parts of streams or rivers with seawater influence, very often from brackish water.

Remarks
When De Man (1892) described Caridina gracilirostris, he noted that there were two forms of carpus in this species: a short carpus form from Sulawesi and a long carpus form from Flores. Tiwari and Pillai (1971) also reported both forms from different parts of the Andaman Islands. Jalihal and Shenoy (1998, p 128), in an abstract for a meeting, commented as follows: ''C. gracilirostris De Man, 1892. Its syntype material is actually an assemblage of three taxonomic forms, viz., a typical and two atypical forms, the 'forma typica' characterized by [the] absence of an appendix interna is actually C. gracilirostris s. s., which is predominantly Indo-Malayan species. Of the two atypical forms, the one possessing a single postorbital tooth and a straight appendix interna and being mainly an African inhabitant with occasional presence in the Malayan archipelago is described as C. n. sp. 1. The other one possessing two postorbital teeth and a curved appendix interna and apparently endemic to Flores is described as C. appendiculata n. subsp. 2.'' No lectotype of C. gracilirostris was formally stated or designated. However, we have discovered that some Madagascan specimens, in RMNH, had been labelled by Jalihal and Shenoy as the types of ''C. appendiculata'', although this information was not published.
Re-examination of the syntypes of C. gracilirostris shows that there are indeed three species. One, the typical form, from Maros and Bapanguipa, Sulawesi, has no appendix interna on the endopod of the male first pleopod; the rostrum has fewer than 10 teeth, there are no postorbital teeth; the telson does not terminate in a posteromedian projection; and the carpus of the first pereiopod is short, less than twice as long as high. A second form, from Bari, Flores, has an endopod on the male first pleopod which possesses a distinct appendix interna, the dorsal margin of the rostrum is armed with more than 10 teeth, of which one or two are situated behind the postorbital margin; the telson terminates in a posteromedian projection; and the carpus of first pereiopod is slender, 2.0-2.5 times as long as high. The third form, from Reo, Flores, has an endopod of male first pleopod which possesses a distinct appendix interna; the rostrum has fewer than 10 teeth, without any postorbital teeth; the telson does not terminate in a posteromedian projection; and the carpus of the first pereiopod is slender, being 2.3-2.9 times as long as high. These three forms are all superficially similar in the form of the rostrum, but can be differentiated from each other easily by the combination of rostral formula and structure of sexual appendages. To stabilize the taxonomic status of these species, we here designate a male specimen from Maros, Sulawesi, as the lectotype of C. gracilirostris. As Jalihal and Shenoy (1998) clearly mentioned the main characters of C. appendiculata in their abstract, their action makes the name available although they did not mention the types even though we know that they had in fact labelled a holotype and paratypes from a series of Madagascan specimens in the RMNH. However, Jalihal and Shenoy's (1998) abstract did not list the type material, although they did state that C. appendiculata was described for the population ''apparently endemic to Flores'' (Jalihal and Shenoy, 1998, p 128) and they referred to De Man's (1892) specimens. This action alone makes De Man's (1892) material from near Bari, Flores, which is now in RMNH, syntypes. Their labelling of the RMNH specimens from Madagascar as the types of C. appendiculata therefore seems odd. This action was probably done after they had decided the species was new and realized later that the material in RMNH from Madagascar was also C. appendiculata, and the species was not just found on Flores. We therefore here designate one of the syntypes of C. gracilirostris (male, cl 3.1 mm, ZMA De 102646), which was from Rive Bari, Flores, as the lectotype of C. appendiculata Jalihal and Shenoy, 1998. Caridina appendiculata is moved to the C. nilotica species group due to the presence of postorbital teeth on the rostrum, a diagnostic character of this group (Y. Cai and P. K. L. Ng, in preparation). The third species, although noted as different by De Man as early as a century ago, remains undescribed, for which the name Caridina neglecta is here proposed.
Caridina pseudogracilirostris Thomas, Pillai, and Pillai, 1976, from Cochin backwater, India, is clearly identical to C. gracilirostris s. str. as the description and the drawings demonstrated, especially in the absence of the appendix interna in the endopod of the male first pleopod. Richard and Chandran (1994) had synonymized C. pseudogracilirostris with C. gracilirostris, although they did not realize that there are actually three species involved in the type series of C. gracilirostris. Holthuis (1965) reported C. gracilirostris from Madagascar. His drawing actually shows C. appendiculata. However, a re-examination of his material shows that one of his lots from Waterolt in Madagascar is indeed C. gracilirostris, the rest being C. appendiculata. Holthuis (1978) also reported C. gracilirostris from Sumba, Lesser Sunda Islands. Re-examination of part of his specimens shows that there are two species involved, C. gracilirostris and C. appendiculata, both from Bondokadi River, West Sumba.
Without detailed descriptions and/or figures of the teeth arrangement, proportions of the various segments of the pereiopods and structure of male first pleopod, the actual identity of many previous records of ''C. gracilirostris'' by various authors cannot be determined for the time being.

Description
Rostrum ending in bifid tip, reaching far beyond distal end of scaphocerite, slightly longer than carapace to 1.6 times as long as carapace, strongly upturned, armed with 5-10 dorsal teeth on posterior half, with 19-24 teeth along whole ventral margin; antennal spine short, situated lower than inferior orbital angle; pterygostomian margin broadly rounded.
Sixth abdominal somite 0.8 times as long as carapace, 1.9 times as long as fifth somite, slightly longer than telson. Telson 3.7 times as long as wide, with four pairs of dorsal spinules and one pair of dorsolateral spinules; distal spines short, stout, lateral pair slightly longer than intermediate spines; lacking posteromedian projection. Preanal carina without spines.
Eyes well developed, anterior end reaching to 0.9 times length of basal segment of antennular peduncle. Antennular peduncle 0.8 times as long as carapace; basal segment of antennular peduncle longer than sum of second and third segment lengths; second segment distinctly longer than third segment. Stylocerite reaching to 0.8 times length of basal segment of antennular peduncle. Scaphocerite very slender, 4.0 times as long as wide.
Mouthparts similar to Caridina neglecta. Palp of first maxilliped ending in a finger-like projection. Second maxilliped typical of genus. Third maxilliped reaching near end of antennular peduncle, with ultimate segment distinctly shorter than penultimate segment.
Epipods on first four pereiopods. First pereiopod not reaching to end of eye stalk; merus 2.4 times as long as broad; carpus slightly longer than merus, 1.6 times as long as high; chela 2.2 times as long as broad, fingers as long as palm. Second pereiopod reaching to end of basal segment of antennular peduncle, merus shorter than carpus, 4.2 times as long as broad; carpus as long as chela, 4.2 times as long as high; chela 3.1 times as long as broad; fingers 1.2 times as long as palm. Third pereiopod reaching to end of antennular peduncle, with propodus 12 times as long as wide, 4.0 times as long as dactylus; dactylus 3.5 times as long as wide (spines included) with six to nine spines on flexor margin. Fifth pereiopod reaching to end of second segment of antennular peduncle, with propodus 14 times as long as wide, 3.2 times as long as dactylus; dactylus 4.0 times as long as wide, with 30-47 spinules on flexor margin.
Endopod of male first pleopod subtriangular, 0.2 times as long as exopod, without appendix interna.

Habitat
A variety of lowland freshwater habitats.

Remarks
With regard to the short carpus of the first pereiopod, and the absence of an appendix interna on the endopod of male pleopod, Caridina gracilima resembles C. gracilirostris. Kemp (1918) differentiated C. gracilima from C. gracilirostris in detail, i.e. in its shorter rostrum; presence of fewer ventral rostral teeth; fewer spinules on the diaeresis of the uropod; relatively larger eggs (0.65-0.70 versus 0.33-0.52 mm) and smaller body size. Based on a larger collection from various localities in Thailand, we find that all these are good characters. Some specimens of C. gracilima, however, have quite a long rostrum, and the ventral rostral teeth also could be as many as 24. Other than the characters mentioned by Kemp, there is one more important character, the absence of a preanal spine, which was mentioned by Bouvier (1925). This character can be effectively used to separate C. gracilima from C. gracilirostris. Woltereck (1937) reviewed the distribution of the genus Caridina and mentioned the variability of the carpus of the first pereiopod in C. gracilirostris, and considered C. gracilima to be indistinguishable from C. gracilirostris. Johnson (1961) followed Woltereck's suggestion, provided a more detailed discussion and treated C. gracilima as a junior synonym of C. gracilirostris. The fact that both authors had not examined any specimens of C. gracilima, and were unaware of the taxonomic confusion within the C. gracilirostris species complex, probably misled them.
The only record for the species outside Thailand was that of Blanco (1935) from the Philippines. According to his description and illustration, his specimens are definitely not C. gracilima. They are most probably C. gracilipes De Man, 1892, instead.
We have examined a series of syntypes of C. gracilima Lanchester, 1901, in MNHN. The best female specimen is here selected as the lectotype of the species.

Distribution
Known with certainty only from Thailand.

Description
Rostrum ending in bifid top, reaching far beyond distal end of scaphocerite, about 1.5-2.0 times as long as carapace, strongly upturned, armed with four to eight dorsal teeth on posterior half and 21-30 teeth along whole ventral margin; antennal spine short, situated below inferior orbital angle; pterygostomial margin sub-rectangular. Sixth abdominal somite 0.6 times as long as carapace, 1.8 times as long as fifth somite, slightly shorter than telson. Telson 3.8 times as long as wide, with three or four pairs of dorsal spinules and one pair of dorsolateral spinules; distal spines short, stout, lateral pair slightly longer than intermediate spines; not ending in a posteromedian projection. Preanal carina with spine.
Eyes well developed, anterior end reaching to 0.7 times length of basal segment of antennular peduncle. Antennular peduncle 0.8 times as long as carapace; basal segment of antennular peduncle longer than sum of second and third segment lengths; second segment distinctly longer than third segment. Stylocerite reaching to 0.8 times length of basal segment of antennular peduncle or near end of this segment. Scaphocerite very slender, 4.2 times as long as wide.
Incisor process of mandible ending in irregular teeth, molar process truncate. Lower lacinia of maxillula broadly rounded, upper lacinia elongate, with numerous distinct teeth on inner margin, palp slender. Upper endites of maxilla subdivided, palp short, scaphognathite tapering posteriorly with some long, curved setae at posterior end. Palp of first maxilliped ending in finger-like projection. Second maxilliped typical of genus. Third maxilliped reaching near end of antennular peduncle, with ultimate segment distinctly shorter than penultimate segment.
Epipods on first four pereiopods. First pereiopod reaching beyond end of eye stalk; merus 3.2-4.0 times as long as broad; carpus slightly longer than merus, 2.3-2.9 times as long as high; chela 2.6 as long as broad, fingers 1.2-1.4 times as long as palm. Second pereiopod reaching beyond end of basal segment of antennular peduncle, merus shorter than carpus, 5.8-6.1 times as long as broad; carpus 1.3-1.4 times as long as chela, 6.2-6.7 times as long as high; chela 2.8-3.0 times as long as broad; fingers 1.3 times as long as palm. Third pereiopod reaching to end of antennular peduncle, propodus 11 times as long as wide, 4.1-5.1 times as long as dactylus; dactylus 2.6 times as long as wide, with six teeth on flexor margin. Fifth pereiopod reaching to end of third segment of antennular peduncle, propodus 15 times as long as wide, 3.7-3.8 times as long as dactylus; dactylus 3.7 times as long as wide, with 37-44 spinules on flexor margin.
Endopod of male first pleopod subtriangular, about 0.25 times as long as exopod, with appendix interna.

Etymology
The species name neglecta alludes to the fact that it has long been neglected as a valid taxon.

Distribution
Known only from Indonesia and Philippines so far, but considering these records, it probably has a wider range.

Remarks
The presence of an appendix interna on the endopod of the male first pleopod easily separates C. neglecta from C. gracilirostris and C. gracilima.

Description
Rostrum ending in bifid tip, reaching far beyond distal end of scaphocerite, about twice as long as carapace, strongly upturned, armed with 8-11 dorsal teeth on posterior half, including none to two postorbital teeth, with 26-33 teeth along whole ventral margin; antennal spine short, situated below inferior orbital angle; pterygostomian margin broadly rounded. Sixth abdominal somite 0.8 times as long as carapace, 2.1 times as long as fifth somite, slightly longer than telson. Telson 3.1 times as long as wide, with four or five pairs of dorsal spinules and one pair of dorsolateral spinules; distal spines short, stout, lateral pair slightly longer than intermediate spines; lacking posteromedian projection. Preanal carina with spine.
Eyes well developed, anterior end reaching to 0.7 times length of basal segment of antennular peduncle. Antennular peduncle 0.8 times as long as carapace; basal segment of antennular peduncle longer than sum of second and third segment lengths; anterolateral angle pointed, reaching 0.3 times length of second segment, second segment distinctly longer than third segment. Stylocerite reaching to 0.8 times length of basal segment of antennular peduncle or near end of this segment. Scaphocerite very slender, 4.2 times as long as wide.
Incisor process of mandible ending in irregular teeth, molar process truncate. Lower lacinia of maxillula broadly rounded, upper lacinia elongate, with distinct teeth on inner margin, palp slender. Upper endites of maxilla subdivided, palp short, scaphognathite tapering posteriorly with some long, curved setae at posterior end. Palp of first maxilliped ending in finger-like projection. Second maxilliped typical of genus. Third maxilliped reaching near end of antennular peduncle, with ultimate segment distinctly shorter than penultimate segment.