Macrobrachium xmas, Fujita & Davie & Ng, 2015

Fujita, Yoshihisa, Davie, Peter J. F. & Ng, Peter K. L., 2015, A new stygobitic prawn of the genus Macrobrachium Spence Bate, 1864, from anchialine caves in Christmas Island, Indian Ocean; with a rediagnosis of M. miyakoense Komai & Fujita, 2005 (Crustacea: Decapoda: Caridea: Palaemonidae), Raffles Bulletin of Zoology 63, pp. 610-625: 612-623

publication ID

http://doi.org/10.5281/zenodo.5386998

publication LSID

lsid:zoobank.org:pub:6754EC0D-D380-44FF-9B94-8FD3BF9934C9

persistent identifier

http://treatment.plazi.org/id/F9B8D695-E10D-4DD7-9870-2DA1263AB1F0

taxon LSID

lsid:zoobank.org:act:F9B8D695-E10D-4DD7-9870-2DA1263AB1F0

treatment provided by

Valdenar

scientific name

Macrobrachium xmas
status

n. sp.

Macrobrachium xmas   n. sp.

( Figs. 4–14 View Fig View Fig View Fig View Fig View Fig View Fig View Fig View Fig View Fig )

Macrobrachium microps   – Short & Meek, 2000: 83–85, fig. 2 [not Macrobrachium microps Holthuis, 1978   ].

Material examined. Holotype: male ( QM-W28315), pocl 18.74 mm, cl 28.30 mm, station CI-23-2011, Freshwater Cave , Christmas Island, coll. 25 March 2011   . Paratypes: 1 ovigerous female ( ZRC 2015.281 View Materials ), pocl 21.66 mm, station CI-21-2010, Whip Cave , coll. 30 January 2010   ; 1 male ( ZRC 2015.282 View Materials ), pocl 16.26 mm, station CI-11-2011, Runaway Cave , coll. 22 March 2011   ; 1 male (RUMF-ZC-2802), pocl 13.22 mm, station CI-19-2011, Runaway Cave , coll. 24 March 2011   ; 1 ovigerous female ( QM-W28316), pocl 20.20 mm, station CI-10-2011, Freshwater Cave , coll. 22 March 2011   ; 1 male ( OUMNH. ZC.2015-02-048), pocl 21.75 mm, station CI-18-2011, Freshwater Cave , coll. 24 March 2011   . Nontypes: 1 male ( WAM-C44840), pocl 12.10 mm, Whip Cave , Christmas Island, coll. by R. D. Brooks & R. Anderson, 30 April 2006   ; 1 male ( ZRC 2015.283 View Materials ), pocl 8.71 mm, station CI-23-2011, Freshwater Cave , coll. 25 March 2011   .

Diagnosis. Medium sized prawn, maximum total length (including rostrum) 67.2 mm in largest male (OUMNH. ZC.2015-02-048). Rostrum slender, over-reaching distal end of antennular peduncle, sometimes reaching or overreaching distal margin of antennal scale, 0.41–0.70 of carapace length; dorsal margin with 12–15 teeth, including 5 or 6 on carapace posterior to orbital margin; ventral margin with 3–8 teeth. Carapace with inferior orbital angle roundly produced; antennal spine large, acute, situated at lower orbital angle, over-reaching inferior orbital angle; hepatic spine sharp, articulated basally, smaller than antennal spine; branchiostegal groove delineated, not extending posteriorly beyond hepatic spine; pterygostomial angle broadly rounded. Fourth and fifth abdominal pleura each acutely produced posteroventrally; inter-uropodal sclerite with median triangular tooth. Eye reduced; stalk swollen anteriorly; cornea faceted with dark pigments, width about 0.71–0.78 of stalk width. First pereiopods very slender, subequal in length, similar in form, over-reaching antennal scale by entire chela and about half of carpus length; chela about half of carpus length. Second pereiopods similar in form, subequal in length, but size and form noticeably different with male larger than female, in large individuals relatively more robust than small ones. Second pereiopods of full-grown male moderately robust, surface of segments profusely spinose, densely setose; palms subcylindrical, about 0.4 of chela length; fingers with cutting edge weakly dentate in proximal half, not noticeably gaping; dactylus 1.2–1.3 times longer than palm; carpus about 0.5 length of chela, 1.0–1.2 length of merus. Ambulatory legs (third to fifth pereiopods) slender, carpi and propodi profusely but minutely spinose, spines minute; fifth pereiopod longer than third or fourth pereiopods, over-reaching antennal scale by length of dactylus and about half of propodus.

Description of holotype. Medium sized prawn, total length (including rostrum) to 63.9 mm. Rostrum ( Fig. 4A–C View Fig ) directed forward, sharply pointed distally, over-reaching distal end of antennular peduncle, but not reaching distal margin of antennal scale, 0.51 of carapace length; dorsal margin slightly rugged, with 15 teeth and rows of plumose setae; 6 teeth extend onto carapace posterior to orbital margin, sixth distal-most tooth bifid; anterior 9 teeth unequally spaced, posterior 6 teeth subequally spaced; ventral margin with 8 unequal teeth with rows of plumose setae, anterior 7 teeth on anterior half and posteriormost tooth on distal half of margin; lateral surface with sharp carina from orbital margin to distalmost. Carapace ( Fig. 4A, C View Fig ) smooth; inferior orbital angle slightly produced; antennal spine large, acute, situated at lower orbital angle, over-reaching inferior orbital angle; hepatic spine sharp, articulated basally, smaller than antennal spine; branchiostegal groove delineated, not extending posteriorly beyond hepatic spine; pterygostomial angle broadly rounded.

Thoracic sternum narrow; fourth sternite with low transverse ridge along posterior border; fifth sternite with prominent paired plates posterior to coxae of second pereiopods; sixth and seventh sternites each with pair of rounded protuberances concealed by coxae of third and fourth pereiopods; eighth sternite with pair of obliquely transverse ridges along posterior border of coxae of fifth pereiopods.

Abdomen ( Fig. 4E View Fig ) with 6 somites, smooth, rounded dorsally; pleura of first 3 somites broadly rounded, fourth and fifth somites each acutely produced posteroventrally; sixth somite 1.41 of fifth somite length, 1.39 times longer than deep, with sharp posterolateral process, posteroventral angle subacute. First 3 abdominal sternites each with transverse ridge and low triangular median tooth, second abdominal sternite more developed than other abdominal sternites; fourth sternite with very small median tubercle; fifth sternite with low median carina; sixth sternite with pair of blunt teeth on posterior margin. Inter-uropodal sclerite ( Fig. 4F, G View Fig ) with conspicuous triangular tooth medially.

Telson ( Fig. 4H, I View Fig ) long, slender, 2.43 times as long as wide, 1.53 times as long as sixth abdominal somite, tapering posteriorly, terminating in blunt tooth: dorsal surface with tuft of plumose setae and 2 pairs of spines, anterior pair of spines arising about midlength of telson; posterior margin with 2 pairs of spines on either side of posteromedian tooth, mesial pair of spines well developed, 3.0 times as long as lateral pair, posteromedian margin with long setae.

Eye ( Fig. 4C, J View Fig ) strongly reduced; stalk short, oblique, swollen anteriorly; cornea small, oblique, faceted with dark pigments, 2.01–2.16 times wider than deep, 0.71–0.73 of stalk width; ocellus not visible.

Antennular peduncle ( Fig. 5A View Fig ) 0.76 times as long as antennal scale. Proximal segment moderately broad, longer than 2 distal segments combined; inner margin sublinear, with numerous plumose setae marginally, 1 short tooth present on ventral side; outer margin somewhat swollen laterally, with marginal plumose setae; distal angle strongly produced, terminating in sharp spine over-reaching proximal margin of third segment of antennular peduncle; stylocerite long, acute, over-reaching midlength of proximal segment; dorsal surface concave, with short or long setae. Middle segment subcylindrical, about 0.45 of proximal segment length, about 1.86 times as long as wide; lateral margins with numerous plumose setae; distal margin with oblique articulation with distal segment. Distal segment subcylindrical, 0.81 of middle segment length, 1.68 times longer than width, anterior and anterolateral margins with some plumose setae. Inner flagellum 0.61 of longer ramus of outer flagellum; outer flagellum biramous, 6 proximal segments fused, shorter ramus about 0.27 length of longer ramus.

Antenna ( Fig. 5B, C View Fig ) with stout basicerite, with 1 strong distoventral tooth (absent on left antenna); ischiocerite and merocerite short; carpocerite cylindrical, reaching 0.34 of antennal scale; flagellum well developed, longer than body. Antennal scale (scaphocerite) with lamella, 2.76 times longer than broad; inner margin somewhat swollen, with numerous marginal setae; outer margin nearly straight, with strong acute tooth on distolateral margin; distal margin broadly rounded, with numerous marginal setae.

Epistome ( Fig. 4D View Fig ) weakly bilobed by shallow depression.

Mouthparts typical of genus. Mandible (left) ( Fig. 5D View Fig ) stout; molar process robust, truncate distally, with 4 blunt peripheral teeth; incisor process large, armed with 3 subequal teeth distally; palp slender, 3-segmented, with marginal setae. Maxillule ( Fig. 5E View Fig ) with tapering coxal endite, with numerous setae distally; basial endite truncate distally, with rows of spines and stiff setae on distal margin; palp (endopod) deeply bilobed, outer lobe somewhat elongate, slender, with some setae on distal margin, inner lobe broad, short, rounded, somewhat curved inwards, with setae distally. Maxilla ( Fig. 5F View Fig ) with coxal endite obsolete; basial endite deeply bilobed, both lobes subequal, with numerous setae marginally; palp (endopod) moderately broad, curved mesially, tapering distally; scaphognathite moderately broad, anterior lobe narrow distally, medial margin deeply emarginate, posterior lobe moderately rounded. First maxilliped ( Fig. 5G View Fig ) with relatively thickened coxal endite, separated from basial endite by narrow notch, bearing numerous setae on distal margin; basial endite suboval, numerous marginal setae; palp (endopod) slender, not reaching distal margin of basial endite; exopod well developed, flagellum long, slender, with long plumose setae distally, caridean lobe moderately broad, with numerous plumose setae marginally; epipod bilobed, anterior lobe larger than posterior. Second maxilliped ( Fig. 5H View Fig ) with coxa rounded mesially, with numerous setae on mesial margin; endopod 5-segmented, basis and ischium fused; carpus with blunt projections at ventrodistal angle; propodus large, oblique articulation with dactylus, with numerous spiniform bristles and setae on mesial margin; dactylus broadly rounded, with numerous spiniform bristles and setae on mesial margin; exopod long, slender, with long plumose setae distally; epipod moderately large, rounded, with well-developed podobranch. Third maxilliped ( Fig. 5I View Fig ) slender, over-reaching distal end of antennular peduncle by tip of distal segment of endopod; coxa feebly produced medially, sparsely setose, with small lateral plate; endopod 3-segmented, long, slender; proximal segment (ischiomeral or antepenultimate segment) incompletely segmented, slightly bowed, swollen and flattened distally, with numerous tufts of setae on medial/lateral margins, 4.23 times longer than greatest width; middle segment (carpus or penultimate segment) with tufts of setae marginally, 0.76 length of proximal segment, 5.07 times longer than greatest width; distal (ultimate) segment tapering to acute claw distally, with numerous setae, 0.72 length of middle segment, 5.10 times longer than proximal width; exopod slender, with plumose setae distally, 0.75 as long as ischiomeral segment.

First pereiopod ( Fig.6A, B View Fig ) very slender, subequal in length, similar in form, over-reaching antennal scale by entire chela and 0.53 of carpus length; basis short, with numerous setae on ventral margin; ischium broad, with numerous setae on ventral margin, 4.31 times longer than greatest width, 0.70 of merus length; merus long, slender, sparsely setose marginally, 7.76 times longer than greatest width, 0.84 of carpus length; carpus very long, 10.26 times longer than distal width, 1.81 length of chela; chela slender, 4.91 times longer than greatest width; palm subcylindrical, 0.46 of chela length, fixed finger terminating in small, curved claw which crosses claw of dactylus, cutting edge entire, with tufts of short setae mesially; dactylus 1.12 of palm length, terminating in small, curved claw, with cutting edge entire, tufts of short setae mesially.

Second pereiopod ( Fig. 6C–I View Fig ) moderately robust, similar in form, subequal in length but right 1.06 times longer than left; surface of dactylus to ischium covered with numerous minute spinules, sparsely setose. Right cheliped ( Fig. 6C–E View Fig ) over-reaching antennal scale by length of entire chela and about 0.5 of carpus length; basis short, with a few minute spinules and some setae on ventral margin; ischium swollen distally, 2.98 times longer than greatest width, 0.77 of merus length; merus 3.92 times longer than greatest width, equal in length to carpus; carpus 3.62 times longer than distal width, 0.51 length of chela; chela 4.89 times longer than greatest width, cutting edge of fingers not gaping; palm subcylindrical, 0.44 of chela length, fixed finger slender, slightly deflexed, terminating in curved, cutting edge thin, proximal margin of cutting edge uneven, with very low, blunt tooth on proximal 0.26; dactylus, 1.21 of palm length, 0.54 of chela length, terminating in curved, acute claw, cutting edge thin, with 5 blunt teeth on 0.36 of entire length, distalmost tooth largest, remaining edge smooth. Left cheliped ( Fig. 6F–I View Fig ) over-reaching antennal scale by length of entire chela and about 0.5 of carpus length; basis short, with a few small spinules and some setae on ventral margin; ischium somewhat swollen distally, 3.19 times longer than greatest width, 0.83 of merus length; merus 3.86 times longer than greatest width, 1.01 times carpus length; carpus 3.81 times longer than distal width, 0.52 length of chela; chela 5.34 times longer than greatest width, cutting edge of fingers not gaping; palm subcylindrical, 0.43 of chela length, fixed finger slender, slightly deflexed, terminating in curved, acute claw crossing claw of dactylus, cutting edge thin, with 1 very low, small tooth on proximal 0.22; dactylus slender, 1.30 times palm length, 0.56 of chela length, terminating in curved, acute claw, cutting edge thin, with 1 low, blunt tooth on 0.32 of entire length.

Ambulatory legs (third to fifth pereiopods) slender. Third pereiopod ( Fig. 7A, B View Fig ) over-reaching antennal scale by length of dactylus and 0.36 of propodus; ischium 3.63 times longer than greatest width, 0.51 of merus length, with some minute spinules on ventral margin; merus 7.35 times longer than greatest width, 1.66 of carpus length, with some minute spinules on dorsal and ventral margins; carpus 5.1 times longer than distal width, 0.65 of propodus length, with minute spinules dorsally; propodus 10.53 times longer than greatest width, with 2 rows of widely spaced spinules on ventral margin and numerous minute spinules on surface; dactylus compressed laterally, feebly curved, terminating in acute tip, unguis not clearly demarcated, 4.08 times longer than proximal depth, 0.31 of propodus length, lateral surface with 5 tufts of short setae along dorsal margin and 4 tufts of setae along ventral margin. Fourth pereiopod ( Fig. 7C, D View Fig ) slightly longer than third pereiopod, over-reaching antennal scale by length of dactylus and 0.55 of propodus; ischium 3.86 times longer than greatest width, 0.52 of merus length; merus 8.68 times longer than greatest width, 1.6 times carpus length; carpus 6.06 times longer than distal width, 0.66 of propodus length, with numerous minute spinules on dorsal surface; propodus 11.07 times longer than depth, with 2 rows of widely spaced spinules on ventral margin and numerous minute spinules on surface; dactylus 4.36 times longer than proximal width, 0.31 of propodus length, lateral surface with 6 tufts of short setae along dorsal margin and 4 tufts of setae along ventral margin. Fifth pereiopod ( Fig. 7E, F View Fig ) longer than third or fourth pereiopods, over-reaching antennal scale by length of dactylus and 0.54 of propodus; coxa with gonopore; ischium 4.67 times longer than greatest width, 0.48 of merus length; merus 9.8 times longer than greatest width, 1.32 of carpus length; carpus 7.93 times longer than distal width, 0.72 of propodus length, with numerous minute spinules on dorsal surface; propodus 14.09 times longer than greatest width, with 2 rows of widely spaced spinules on ventral margin and numerous minute spinules on surface, with subdistal tufts of grooming setae; dactylus 4.44 times longer than proximal width, 0.26 of propodus length, lateral surface with 6 tufts of short setae along dorsal margin and 2 tufts of setae along ventral margin.

First pleopod with moderately stout protopod; endopod ( Fig. 5J View Fig ) about 0.49 of exopod length, weakly curved mesially, rounded distally, ventral surface concave, fringed with plumose setae marginally. Second pleopod with appendix masculina ( Fig. 5K View Fig ) elongate, slender, 0.6 of endopod length, with numerous setae; appendix interna slender, 0.56 of appendix masculina.

Uropod ( Fig. 4E View Fig ) with protopod bearing strong acute posterolateral tooth; endopod 0.96 of exopod length; exopod over-reaching tip of telson, lateral margin straight, terminating in small acute tooth at about 0.86 of length, with small movable spine just mesial to posterolateral tooth.

Notes on paratypes. All paratype specimens examined, including full-grown male/female (pocl 13.22–21.75 mm), are basically similar to the holotype, but some variation occurs: rostrum can be relatively more slender, varying in shape and length, 0.48–0.70 of carapace length, over-reaching distal end of antennular peduncle, reaching or over-reaching distal margin of antennal scale to different degrees; dorsal margin of the rostrum armed with 12 or 13 teeth, with 5 or 6 on carapace posterior orbital margin; ventral margin with 3–8 teeth; cornea of eye 1.89–2.15 times wider than deep, 0.75–0.78 of stalk width. The rostrum of the largest male (pocl 21.75 mm) appears atypical ( Fig. 8A View Fig ), with unusual anterior margins, suggesting that it had probably been damaged and regrown; it is relatively shorter, being only 0.41 of carapace length, and does not over-reach the distal end of the antennular peduncle. Second pereiopods similar in form, subequal in length, but varied in size and shape due to growth and sexual features; male larger than female, and large individuals relatively more robust than smaller ones ( Figs. 8–12 View Fig View Fig View Fig View Fig View Fig ); the carpi of ovigerous females (pocl 20.20 mm, QM-W28316; pocl 21.66 mm, ZRC 2015.281) slightly longer than that in males (carpi 0.61–0.66 of chela length in females vs. 0.48–0.53 in males); the length of dactylus to palm in smaller males (pocl 16.26 mm, ZRC 2015.282; pocl 13.22 mm, RUMF-ZC-2802) is distinctly shorter than that in large males (ratio of 1.56–1.75 in smaller males versus 1.21–1.35 in large males) ( Figs. 8–12 View Fig View Fig View Fig View Fig View Fig ).

Color in life. Whole body (carapace, abdomens, and appendages) generally whitish to pale yellow ( Figs. 13, 14 View Fig ).

Habitat and biology. Macrobrachium xmas   n. sp. was collected from three anchialine caves (Freshwater Cave, Runaway Cave and Whip Cave). Specific habitat information for these localities has been given by Humphreys & Eberhard (2001). Co-inhabiting decapod crustaceans reported from Christmas Island caves include: a procaridid Procaris noelensis Bruce & Davie, 2006   , an alpheid Metabetaeus minutus ( Whitelegge, 1897)   , a barbouriid Parhippolyte   cf. uveae Borradaile, 1899, an atyid Antecaridina lauensis ( Edmondson, 1935)   , and three crabs, Karstarma jacksoni ( Balss, 1934)   [ Sesarmidae   ], Orcovita hicksi Davie & Ng, 2012   , and Orcovita orchardorum Davie & Ng, 2012   [both Varunidae   ] ( Anker, 2010; Bruce & Davie, 2006; Davie & Ng, 2012). In this study, two ovigerous females of M. xmas   were collected, and the pre-eyed eggs are small, 0.56–0.70 mm (on female pocl 21.66 mm, ZRC 2015.281, average 0.64 mm, n = 10) in size, suggesting an amphidromous life cycle.

Distribution. Only known from Christmas Island thus far.

Etymology. The new species name is a common arbitrary abbreviation of “Christmas” and is derived from the type locality, Christmas Island. The name is used as a noun in apposition.

Remarks. Among the 12 stygobitic Macrobrachium species   , it is known that M. gua   , and M. lucifugum   , have well developed eyes like their epigean congeners (see Chong, 1989; Holthuis, 1974) and therefore can easily be distinguished from the present new species. On the other hand, M. elegantum   , M. villalobosi   and M. lingyunense   are also readily separated from the present new species by lacking faceted corneas ( M. villalobosi   and M. lingyunense   ) or lacking pigmented corneas ( M. elegantum   ) (see Hobbs, 1973; Li et al., 2006; Pan et al., 2010). Macrobrachium acherontium   , M. cavernicola   and M. sbordonii   can be easily distinguished from M. xmas   by having even more reduced corneas and having fewer dorsal rostral teeth (7–11 teeth in M. acherontium   , 5–9 in M. cavernicola   , 7 in M. sbordonii   , versus 12–15 teeth in M. xmas   ) (cf. Figs. 4 View Fig , 8–12 View Fig View Fig View Fig View Fig View Fig ; Kemp, 1924; Holthuis, 1977; Mejía-Ortíz et al., 2008). In addition to these differences, M. cavernicola   can be separated from M. xmas   by having the following characters: (1) mandibular palp is 2-segmented ( Kemp, 1924: pl. 3, fig. 4) (3-segmented in M. xmas   , Fig. 5D View Fig ), (2) the dactyli of the second pereiopods are thinly coated by “dark brown fur” ( Kemp, 1924: pl. 3, fig. 1) (absent in M. xmas   , Fig. 6C–H View Fig ), and the carpi of the second pereiopods are proportionally shorter ( Kemp, 1924: pl. 3, fig. 1) than in M. xmas   ( Fig. 6C, F View Fig ) (0.27–0.34 of the chela length versus about 0.5). In the morphology of the second pereiopod, M. acherontium ( Holthuis, 1977)   and M. sbordonii   ( Mejía-Ortíz et al., 2008: figs. 2A, 3E) differ from M. xmas   by having a proportionally longer carpus (0.8–0.9 of the chela length in M. acherontium   versus about 0.5 in M. xmas   ; and twice the chela length in M. sbordoni   versus 1.18–1.59 in M. xmas   ) (cf. Fig. 6C, F View Fig ).

Macrobrachium poeti   differs from M. xmas   by the proportionally broader rostrum, having fewer ventral rostral teeth [1–2 versus 3–8 teeth in M. xmas   (cf. Figs. 4 View Fig , 8-12 View Fig View Fig View Fig View Fig View Fig ; Holthuis, 1984: fig. 1a), the smooth second pereiopod ( Holthuis, 1984: fig. 1e, f) (profusely spinose in M. xmas   , Fig. 6C, F View Fig ), and the proportionally shorter second pereiopod carpus ( Holthuis, 1984: fig. 1e) (about 0.3 of the chela length versus about 0.5 in M. xmas   , Fig. 6C, F View Fig ).

Macrobrachium catonium   can be distinguished from M. xmas   by the relatively broader rostrum with fewer dorsal rostral teeth (6–9 versus 12–15 in M. xmas   ), and the proportionally longer second pereiopod carpus (1.2 times as long as propodus versus about 0.5 in M. xmas   ) (cf. Fig. 6C, F View Fig ; Hobbs & Hobbs, 1995: fig. 1a).

Based on the present description of additional adult male and female specimens of Macrobrachium miyakoense   , it is clear that this species is morphologically very similar to M. xmas   . However, M. xmas   can be distinguished by the relatively longer and more slender rostrum (cf. Figs. 1A View Fig , 2A View Fig , 4A View Fig , 9A View Fig , 10A View Fig , 11A View Fig ; Fujita & Komai, 2005: figs. 2B, 6A), the slightly smaller eye cornea [0.71–0.78 of stalk width vs. about 0.8 (0.82–0.83) in M. miyakoense   ], the proportionally more swollen eye stalk (cf. Figs. 1B View Fig , 2B View Fig , 4J View Fig , 8B View Fig , 9B View Fig , 10B View Fig , 11B View Fig , 12B View Fig ; Komai & Fujita, 2005: fig. 2C), and by having more teeth on the post-rostral margin of the carapace (5 or 6 versus 4 in M. miyakoense   ) (cf. Figs. 1A View Fig , 2A View Fig , 4A View Fig , 8A View Fig , 9A View Fig , 10A View Fig , 11A View Fig , 12A View Fig ; Fujita & Komai, 2005: figs. 2A, 6A).

The taxonomy of Macrobrachium microps   is, in our opinion, somewhat confused, and it may currently include several quite similar species. Macrobrachium microps   was originally described from the Danmin Cave in New Ireland, Papua New Guinea, and later recorded from Samoa, New Caledonia (Lifou Island), and Christmas Island ( Holthuis, 1978; Bruce & Iliffe, 1993; Short & Marquet, 1998; Short & Meek, 2000). The holotype of M. microps   is not in Naturalis (Leiden), and may have been returned to the collector from Bulgaria (Sammy De Grave, personal communication). The holotype of M. microps   (cl 22.0 mm) can be easily distinguished from M. xmas   by the slightly shorter rostrum (cf. Fig. 4C View Fig , 8A View Fig , 9A View Fig , 10A View Fig , 11A View Fig , 12A View Fig ; Holthuis, 1978: fig. 1a, b), the more reduced cornea (slightly more than half of the eyestalk width versus about 0.71–0.78 in M. xmas   ) (cf. Fig. 4C, J View Fig ; Holthuis, 1978: fig. 1b), and the remarkably larger and stouter second pereiopods (cf. Fig. 6C, F View Fig ; Holthuis, 1978: fig. 1f–h). In addition to those differences, it is different from M. xmas   in the shape and armature of the second pereiopods: (1) the second pereiopods are obviously unequal and dissimilar in M. microps   , whereas they are similar and subequal in M. xmas   ; (2) the cutting edge of the major chela bears large teeth between which there is a distinct gap, whereas the cutting edges are armed with very low, blunt tooth on the proximal margin, and lack the gap between fingers, in M. xmas   ; (3) the dactylus of the major chela is distinctly shorter and slightly more than half as long as the palm in M. microps   , whereas the dactyli of both chelae is 1.2–1.3 of the palm length in M. xmas   ; and (4) the minor chela bears numerous long stiff setae on the cutting edges of the fingers (such that they fill the gap between the fingers) in M. microps   , whereas M. xmas   lacks any such setae (cf. Fig. 6C–I View Fig ; Holthuis, 1978: fig. 1).

Short & Meek (2000) reported M. microps   from Christmas Island based on an adult female (pocl 23.8 mm) and young male (pocl 11.9 mm) from Daniel Roux Cave and Freshwater Cave, respectively. Although the diagnosis they gave was very brief, the female they described agrees well with our samples of M. xmas   . The young male differs a little in having only 4 teeth on the carapace posterior to the dorsal margin ( Short & Meek, 2000: Fig. 2A View Fig ); and by the second pereiopods lacking setal pubescence ( Short & Meek, 2000: Fig. 2B View Fig ). Although we borrowed the available specimens of Macrobrachium   from Christmas Island from WAM, the two specimens studied by Short & Meek (2000) were not among the material and we are not sure where they are. The present WAM material from Whip and Freshwater Caves are small males (non-types: WAM-C44840, pocl 12.1 mm; ZRC 2015.283, pocl 8.71 mm), here referred to M. xmas   . We did not manage to collect any specimens of M. xmas   from Daniel Roux Cave but had several specimens (including the holotype) from Freshwater Cave.

The smallest male (pocl 8.71 mm, ZRC 2015.283) has no second pereiopods, but the number of post-rostral teeth of the carapace is the same (only 4 teeth) as the “young male” reported by Short & Meek (2000: fig. 2A). The second pereiopods of WAM-C44840 (pocl 12.1 mm) also resemble those of Short & Meek (2000) in having only a few setal setae on the surface. We believe such differences are likely to be developmental in nature, and as such, we here refer their record of M. microps   from Christmas Island to the present new species. We also examined 62 juveniles of “ Macrobrachium sp.   ” from Christmas Island (pocl 2.5-12.1 mm: WAM-C44823, C44824 View Materials , C44825 View Materials , C44826 View Materials , C44827 View Materials , C44828 View Materials , C44829 View Materials , C44830 View Materials , C44831 View Materials , C44832 View Materials , C44833 View Materials , C44834 View Materials , C44835 View Materials , C44836 View Materials , C44837 View Materials , C44839 View Materials , C44840 View Materials ) which were collected from cave systems but only 1 male (WAM-C44840, pocl 12.1 mm) could be indentified as M. xmas   and all of the rest are young of M. lar ( Fabricius, 1798)   . The eyes of these specimens were not at all reduced, with the ocellus still clearly visible, and there was only one tooth on the post-rostral margin of the carapace (even in the largest pocl 6.1 mm specimen). Although we did not catch or observe adult M. lar   inside the caves (they are otherwise common in epigeal waters in Christmas Island ( Ng & Davie, 2012), they have been found in subterranean waters in the Ryukyus ( Komai & Fujita, 2005; first author, unpublished data).

Bruce & Iliffe (1993) reported one young male of M. microps   (pocl 13.1 mm) from Upolu, Samoa. Their specimen is obviously different from the holotype of M. microps   by characters of the rostrum, second pereiopods, and ambulatory pereiopods (see Holthuis, 1978; Bruce & Iliffe, 1993). Komai & Fujita (2005) had already pointed out that the Samoan specimen might represent an undescribed species. In any case, this Samoan specimen can be readily distinguished from M. xmas   by the relatively shorter rostrum, that does not reach the distal end of the antennular peduncle (rostrum over-reaches the distal end of the antennular peduncle in M. xmas   ), and the more reduced eye cornea (0.5 of stalk width versus 0.71–0.78 in M. xmas   ) (cf. Figs. 4A, C, J View Fig , 8B View Fig , 9 View Fig A-B, 10A, B, 11A, B, 12A, B; Bruce & Iliffe, 1993: figs. 1, 2A–D, H).

Short & Marquet (1998) reported two males (pocl 21.6 mm and 23.1 mm) of M. microps   from Lifou Island, New Caledonia. The specimens illustrated ( Short & Marquet, 1998: fig. 1A) are more similar to M. xmas   than they are to the holotype of M. microps   . In particular, they share with M. xmas   : (1) the carapace posterior to the dorsal margin bears 5 teeth; and, (2) the rostrum is long and slender, over-reaching the distal end of the antennular peduncle. The description by Short & Marquet (1998) is too brief, and it is difficult to compare with M. xmas   in detail, however we believe that the material reported as M. microps   from New Caledonia may represent another new species. The New Caledonian taxon differs mainly from M. xmas   because the second pereiopods lack setal pubescence, whereas the surface of the second pereiopods is profusely spinose and setose even in similar size (pocl 21.66 mm and 20.20 mm) females of M. xmas   ( Figs. 11C, D View Fig , 12C, D View Fig ).

ZC

Zoological Collection, University of Vienna

R

Departamento de Geologia, Universidad de Chile

Kingdom

Animalia

Phylum

Arthropoda

Class

Malacostraca

Order

Decapoda

Family

Palaemonidae

Genus

Macrobrachium

Loc

Macrobrachium xmas

Fujita, Yoshihisa, Davie, Peter J. F. & Ng, Peter K. L. 2015
2015
Loc

Macrobrachium microps

Short J & Meek P 2000: 83
2000