Fujita et al.: New stygobitic prawn of the genus Macrobrachium
Taxonomy & Systematics
RAFFLES BULLETIN OF ZOOLOGY 63: 610–625

Date of publication: 25 December 2015
http://zoobank.org/urn:lsid:zoobank.org:pub:6754EC0D-D380-44FF-9B94-8FD3BF9934C9

A new stygobitic prawn of the genus Macrobrachium Spence Bate,
1864, from anchialine caves in Christmas Island, Indian Ocean; witha rediagnosis of M. miyakoense Komai & Fujita, 2005 (Crustacea:
Decapoda: Caridea: Palaemonidae)
Yoshihisa Fujita1*, Peter J. F. Davie2 and Peter K. L. Ng3
Abstract. A new species of stygobitic palaemonid prawn of the genus Macrobrachium Spence Bate, 1864, is
described from Christmas Island, Indian Ocean Territory, Australia. The new anchialine species resembles M.
miyakoense Komai & Fujita, 2005, from Japan, but can be distinguished by its relatively longer and more slenderrostrum, the proportionately smaller eye cornea with a more swollen eye stalk, and more teeth on the post-rostral
margin of the carapace. The taxonomy of M. miyakoense is also discussed based on additional material recently
obtained from Japan, and the species rediagnosed. Macrobrachium miyakoense was originally described from two
young males collected from Miyako Island, Ryukyu Islands, Japan.
Key words. Palaemonidae, Macrobrachium, new species, anchialine cave, Christmas Island, Indian Ocean, taxonomy

INTRODUCTION

In Christmas Island, Indian Ocean Territory, Australia,
there are extensive subterranean habitats with a significant
subterranean fauna (Humphreys & Eberhard, 2001),
including endemic decapods such as the shrimp Procaris
noelensis Bruce & Davie, 2006, and two species of varunid
crab, Orcovita orchardorum Davie & Ng, 2012, and O.
hicksi Davie & Ng, 2012. As for freshwater palaemonids,
Macrobrachium lar (Fabricius, 1798) has been reported fromsurface waters on the island, where it is relatively common(De Man, 1906; Short & Meek, 2000; Ng & Davie, 2012).
Gordon (1935: 629) also listed M. rosenbergii (De Man,
1879) (as Palaemon carcinus) from the island but there
have been no records since (e.g., Short & Meek, 2000).
We have not obtained this species in our surveys and it isunlikely such a large and distinctive species would havebeen missed. This record is almost certainly a mistake as
there are no suitable habitats on Christmas Island for thisspecies (e.g., large freshwater rivers) (see Wowor & Ng,2007). A third species, M. microps, was recorded by Short& Meek (2000) on the basis of one adult female (pocl 23.8mm) specimen from Daniel Roux Cave, and an undeveloped
male (pocl 11.9 mm) from Freshwater Cave. This species
was originally described from the Danmin Cave in New
Ireland, Papua New Guinea, and thereafter recorded from
Samoa and New Caledonia (Lifou Island) (Holthuis, 1978;
Bruce & Iliffe, 1993; Short & Marquet, 1998).

Macrobrachium Spence Bate, 1864, is the most diverse
genus in the family Palaemonidae with around 245 species(De Grave & Fransen, 2011). Its species have adapted wellto many freshwater and estuarine habitats (e.g., Holthuis,
1986; Chace & Bruce, 1993), but relatively few have madethe move into subterranean environments. Currently, there
are 12 stygobitic species of Macrobrachium described:
M. acherontium Holthuis, 1977 [Mexico], M. catonium
Hobbs & Hobbs, 1995 [Belize], M. cavernicola (Kemp,
1924) [Assam, India], M. elegantum Pan, Hou & Li, 2010
[Guangxi, China], M. gua Chong 1989 [Sabah, Borneo],
M. lingyunense Li, Cai & Clarke, 2006 [Guangxi, China],
M. lucifugum Holthuis, 1974 [Cuba and nearby islands], M.
microps Holthuis, 1978 [New Ireland, Papua New Guinea;
New Caledonia and Samoa], M. miyakoense Komai &Fujita, 2005 [Ryukyus, Japan], M. sbordonii Mejía-Ortíz,
Baldari & López-Mejía, 2008 [Chiapas, Mexico], M. poeti
Holthuis, 1984 [Java, Indonesia], and M. villalobosi Hobbs,
1973 [Oaxaca, Mexico] (see Holthuis, 1986; Li et al., 2006;
Mejía-Ortíz et al., 2008; Pan et al., 2010).

Okinawa Prefectural University of Arts, 1-4 Shuri-tounokura, Naha, Okinawa 9038602, Japan; Email: fujitayo@okigei.ac.jp (*corresponding author)
1

One of the objectives of the Christmas Island Expeditions
conducted in January–February 2010, March 2011 andFebruary 2012 (see Tan et al., 2014a, b), was to collect
more adult specimens of the stygobiotic Macrobrachium,including adult males and females, to verify the identificationof Short & Meek (2000). After detailed examination of
the new specimens collected, we are now confident that

Queensland Museum, PO Box 3300, South Brisbane, Queensland, Australia; Email:Peter.Davie@qm.qld.gov.au
2

Lee Kong Chian Natural History Museum, Faculty of Science, National Universityof Singapore, 2 Conservatory Drive, Singapore 117377, Republic of Singapore;
Email: dbsngkl@nus.edu.sg
3© National University of Singapore
ISSN 2345-7600 (electronic) | ISSN 0217-2445 (print)

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Fig. 1. Macrobrachium miyakoense Komai & Fujita, 2005, adult male (pocl 18.9 mm) from Miyako Island, Ryukyu Islands, Japan (RUMFZC-2665). A, rostrum, carapace, and cephalic appendages, lateral view; B, eye (left side), ventral view (left), dorsal view (right); C, leftsecond pereiopod, lateral view; D, same, chela (setae and spinules omitted); E, same, basal part of fingers, dorsal view; F, right second
pereiopod, lateral view; G, same, basal part of fingers, dorsal view. Scale bars = 1.0 mm.

Fig. 2. Macrobrachium miyakoense Komai & Fujita, 2005, adult female (pocl 21.8 mm) from Miyako Island, Ryukyu Islands, Japan(RUMF-ZC-2664). A, rostrum, carapace, and cephalic appendages, lateral view; B, eye (left side), ventral view; C, left second pereiopod;D, right second pereiopod; E, same, basal part of fingers, dorsal view. Scale bars = 1.0 mm.

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our specimens have sufficient differences from known
species to recognise them as belonging to a new species,
Macrobrachium xmas n. sp.; and specimens which have has
been reported as “M. microps” by Short & Meek (2000) areprobably also conspecific with the new species. This new
species most closely resembles M. miyakoense from Japan,
a species described on the basis of two small specimens.
Fortunately, the first author (YF) has since collected two
more adult specimens of M. miyakoense from an anchialine
cave near the type locality in Japan. This additional material
has allowed us to make more detailed comparisons with M.
xmas n. sp. The opportunity is thus also taken to redescribe
M. miyakoense on the basis of the new adult material.

depression. Male (RUMF-ZC-2665): second pereiopods(Fig. 1C, D, E) moderately robust, similar in form, unequalin length; left 1.68 times longer than right; surface fromdactylus to ischium covered with numerous minute spinules,
sparsely setose. Left (major) cheliped robust; ischium 0.68
of merus length; merus 1.01 of carpus length; carpus 0.58
length of chela; palm subcylindrical, 0.43 of chela length,
dactylus 1.38 of palm length, 0.59 of chela length; cuttingedge of fingers not gaping, with low, blunt teeth on proximal
margins. Right (minor) cheliped (Fig. 1F, G) slender; ischium
0.78 of merus length; merus 1.12 of carpus length; carpus
0.55 length of chela; palm 0.40 of chela length; dactylus,
1.46 of palm length, 0.59 of chela length; cutting edgeof fingers almost smooth, not gaping. Female (RUMFZC-2664): second pereiopods (Fig. 2C, D, E) moderately
slender, similar in form, equal in length; surface of dactylus
to ischium covered with sparsely minute spinules and setose;ischium 0.72–0.75 of merus length; merus 1.14–1.16 of
carpus length; carpus 0.55–0.56 length of chela; palm 0.39
of chela length; dactylus 1.60–1.61 of palm length, 0.62 ofchela length; cutting edge of fingers not gaping, with very
low, blunt teeth on proximal margins.

MATERIAL AND METHODSSpecimens were collected by using collapsible bait traps andtubular plastic shrimp/crab traps (of a type commonly usedin Taiwan). Size of specimens is indicated by postorbital
carapace length (pocl) measured from the orbital margin to
the posterodorsal margin of the carapace. The abbreviation
cl is used for carapace length (including the rostrum). The
types specimens of the present new species are deposited in
the following collections: ZRC – the Zoological ReferenceCollection of the Lee Kong Chian Natural History Museum,
National University of Singapore; QM – the Queensland
Museum, Brisbane; WAM – the Western AustralianMuseum, Perth; OUMNH.ZC – Oxford University Museumof Natural History, Oxford, U.K.; RUMF – the Ryukyu
University Museum, Fujukan, Okinawa, Japan. We follow
the classification and citation of authorities outlined in De
Grave & Fransen (2011).

Remarks. Macrobrachium miyakoense was originallydescribed from two young males (pocl 14.70 mm and12.60 mm). The present full-grown specimens are similar
in morphology to the type specimens, but some adultcharacters differ markedly. We have therefore amended theoriginal description of Komai & Fujita (2005) accordingly
and provided new figures.
Macrobrachium xmas n. sp.
(Figs. 4–14)

TAXONOMY

Macrobrachium microps – Short & Meek, 2000: 83–85, fig. 2 [notMacrobrachium microps Holthuis, 1978].

Family Palaemonidae

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), pocl 21.66 mm, station
CI-21-2010, Whip Cave, coll. 30 January 2010; 1 male (ZRC
2015.282), 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), pocl 8.71 mm, station
CI-23-2011, Freshwater Cave, coll. 25 March 2011.

Macrobrachium miyakoense Komai & Fujita, 2005
(Figs. 1–3)
Macrobrachium miyakoense – Komai & Fujita, 2005: 14; De Grave& Fransen, 2011: 327.

Material examined. 1 female (RUMF-ZC-2664), pocl 21.8mm, Ueno Ana-ga Cave, Miyako Island, 24°43’13.9”N,
125°19’19.5”E, Ryukyu Islands, Japan, baited trap, coll. by
Y. Fujita, 15 September 2009; 1 male (RUMF-ZC-2665),
pocl 18.9 mm, Ueno Ana-ga Cave, Miyako Island, Ryukyu
Islands, Japan, baited trap, coll. by Y. Fujita, 15 August 2010.
Supplementary description. Compared to types, rostrum(Figs. 1A, 2A) directed anteriorly, sharply pointed distally,reaching/over-reaching distal end of antennular peduncle,
not reaching distal margin of antennal scale, 0.45–0.52 ofcarapace length; dorsal margin with 10 teeth, 4 on carapace
posterior to orbital margin; ventral margin with 4 or 5 teeth.
Eye (Figs. 1B, 2B) reduced; stalk short, oblique, weakly
swollen anteriorly; cornea small, oblique, faceted with dark
pigments, 1.91–1.97 times wider than deep, 0.82–0.83 stalkwidth; ocellus absent. Epistome weakly bilobed by shallow

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 ofcarapace length; dorsal margin with 12–15 teeth, including
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Fig. 3. Macrobrachium miyakoense Komai & Fujita, 2005, coloration of live specimens. A, adult male (RUMF-ZC-2665), dorsal view;
B, same, lateral view; C, adult female (RUMF-ZC-2664), dorsal view; D, same, lateral view.

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 atlower 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 eachacutely produced posteroventrally; inter-uropodal scleritewith 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 ofchela, 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 bylength 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)
directed forward, sharply pointed distally, over-reaching distal
end of antennular peduncle, but not reaching distal marginof 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 fromorbital margin to distalmost. Carapace (Fig. 4A, C) 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, notextending posteriorly beyond hepatic spine; pterygostomial
angle broadly rounded.

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Fig. 4. Macrobrachium xmas n. sp., holotype male (pocl 18.74 mm) (QM-W28315). A, rostrum and carapace, lateral view; B, tip ofrostrum, lateral view; C, rostrum, anterior part of carapace and cephalic appendages, dorsal view; D, epistome, venral view; E, abdomen
and telson, and left uropod, lateral view: F, posterior margin of sixth abdominal sternite and interuropodal sclerite, ventrolateral view;G, same, ventral view; H, telson, dorsal view; I, posterior margin of telson, dorsal view; J, eye (left side), ventral view (above), dorsal
view (below). Scale bars = 1.0 mm.

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

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) weakly bilobed by shallow depression.

Antennular peduncle (Fig. 5A) 0.76 times as long as antennal
scale. Proximal segment moderately broad, longer than 2
distal segments combined; inner margin sublinear, withnumerous 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 marginof 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.

Mouthparts typical of genus. Mandible (left) (Fig. 5D) 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) with tapering coxal endite, with numerous
setae distally; basial endite truncate distally, with rows ofspines and stiff setae on distal margin; palp (endopod) deeply
bilobed, outer lobe somewhat elongate, slender, with somesetae on distal margin, inner lobe broad, short, rounded,somewhat curved inwards, with setae distally. Maxilla (Fig.
5F) 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) withrelatively thickened coxal endite, separated from basialendite by narrow notch, bearing numerous setae on distal
margin; basial endite suboval, numerous marginal setae;
palp (endopod) slender, not reaching distal margin of basialendite; exopod well developed, flagellum long, slender, withlong plumose setae distally, caridean lobe moderately broad,with numerous plumose setae marginally; epipod bilobed,
anterior lobe larger than posterior. Second maxilliped (Fig.
5H) 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, withnumerous spiniform bristles and setae on mesial margin;
dactylus broadly rounded, with numerous spiniform bristles
and setae on mesial margin; exopod long, slender, with longplumose setae distally; epipod moderately large, rounded,with well-developed podobranch. Third maxilliped (Fig.
5I) 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 (ischiomeralor antepenultimate segment) incompletely segmented, slightly
bowed, swollen and flattened distally, with numerous tufts
of setae on medial/lateral margins, 4.23 times longer thangreatest width; middle segment (carpus or penultimate
segment) with tufts of setae marginally, 0.76 length ofproximal segment, 5.07 times longer than greatest width;
distal (ultimate) segment tapering to acute claw distally, withnumerous 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.

Antenna (Fig. 5B, C) with stout basicerite, with 1 strong
distoventral tooth (absent on left antenna); ischiocerite andmerocerite short; carpocerite cylindrical, reaching 0.34 ofantennal scale; flagellum well developed, longer than body.
Antennal scale (scaphocerite) with lamella, 2.76 times longer

First pereiopod (Fig.6A, B) 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,

Abdomen (Fig. 4E) 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, withsharp posterolateral process, posteroventral angle subacute.
First 3 abdominal sternites each with transverse ridge andlow triangular median tooth, second abdominal sternite moredeveloped than other abdominal sternites; fourth sternite withvery small median tubercle; fifth sternite with low mediancarina; sixth sternite with pair of blunt teeth on posterior
margin. Inter-uropodal sclerite (Fig. 4F, G) with conspicuous
triangular tooth medially.
Telson (Fig. 4H, I) 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 withtuft of plumose setae and 2 pairs of spines, anterior pair ofspines 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 aslateral pair, posteromedian margin with long setae.
Eye (Fig. 4C, J) 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 ofstalk width; ocellus not visible.

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Fig. 5. Macrobrachium xmas n. sp., holotype male (pocl 18.74 mm) (QM-W28315). Left appendages. A, antennule, ventral view; B,
antenna, ventral view; C, basal part of right antenna, ventral view; D, mandible, ventral view; E, maxillule, ventral view; F, maxilla, ventral
view; G, first maxilliped, ventral view; H, second maxilliped, ventral view; I, third maxilliped, lateral view; J, endopod of first pleopod,
ventral view; K, appendix interna and appendix masculine of second pleopod, mesial view. Scale bars = 1.0 mm.

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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 ofchela length, fixed finger terminating in small, curved claw
which crosses claw of dactylus, cutting edge entire, withtufts of short setae mesially; dactylus 1.12 of palm length,
terminating in small, curved claw, with cutting edge entire,
tufts of short setae mesially.

with 5 tufts of short setae along dorsal margin and 4 tufts ofsetae along ventral margin. Fourth pereiopod (Fig. 7C, D)
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 ofpropodus length, with numerous minute spinules on dorsal
surface; propodus 11.07 times longer than depth, with 2 rowsof widely spaced spinules on ventral margin and numerous
minute spinules on surface; dactylus 4.36 times longer thanproximal 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)
longer than third or fourth pereiopods, over-reaching antennal
scale by length of dactylus and 0.54 of propodus; coxa withgonopore; 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 minutespinules on dorsal surface; propodus 14.09 times longer thangreatest width, with 2 rows of widely spaced spinules onventral 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, lateralsurface with 6 tufts of short setae along dorsal margin and2 tufts of setae along ventral margin.

Second pereiopod (Fig. 6C–I) moderately robust, similar inform, subequal in length but right 1.06 times longer thanleft; surface of dactylus to ischium covered with numerous
minute spinules, sparsely setose. Right cheliped (Fig. 6C–E)
over-reaching antennal scale by length of entire chela andabout 0.5 of carpus length; basis short, with a few minutespinules 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, equalin length to carpus; carpus 3.62 times longer than distal
width, 0.51 length of chela; chela 4.89 times longer thangreatest 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) 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 thangreatest 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, acuteclaw crossing claw of dactylus, cutting edge thin, with 1very low, small tooth on proximal 0.22; dactylus slender,
1.30 times palm length, 0.56 of chela length, terminatingin curved, acute claw, cutting edge thin, with 1 low, blunt
tooth on 0.32 of entire length.

First pleopod with moderately stout protopod; endopod (Fig.
5J) about 0.49 of exopod length, weakly curved mesially,rounded distally, ventral surface concave, fringed withplumose setae marginally. Second pleopod with appendix
masculina (Fig. 5K) elongate, slender, 0.6 of endopod
length, with numerous setae; appendix interna slender, 0.56
of appendix masculina.
Uropod (Fig. 4E) with protopod bearing strong acuteposterolateral tooth; endopod 0.96 of exopod length; exopod
over-reaching tip of telson, lateral margin straight, terminatingin 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 inshape 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), with unusual
anterior margins, suggesting that it had probably beendamaged 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, andAmbulatory legs (third to fifth pereiopods) slender. Third
pereiopod (Fig. 7A, B) over-reaching antennal scale bylength of dactylus and 0.36 of propodus; ischium 3.63
times longer than greatest width, 0.51 of merus length, withsome minute spinules on ventral margin; merus 7.35 times
longer than greatest width, 1.66 of carpus length, with someminute spinules on dorsal and ventral margins; carpus 5.1
times longer than distal width, 0.65 of propodus length, withminute spinules dorsally; propodus 10.53 times longer thangreatest width, with 2 rows of widely spaced spinules onventral margin and numerous minute spinules on surface;
dactylus compressed laterally, feebly curved, terminating inacute tip, unguis not clearly demarcated, 4.08 times longer
than proximal depth, 0.31 of propodus length, lateral surface
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Fujita et al.: New stygobitic prawn of the genus Macrobrachium

Fig. 6. Macrobrachium xmas n. sp., holotype male (pocl 18.74 mm) (QM-W28315). Chelipeds. A, first pereiopod, lateral view; B, chelaof first pereiopod, ventral view; C, right second pereiopod, lateral view; D, same, tip of dactylus, dorsal view; E, same, basal part offingers, dorsal view; F, left second pereiopod, lateral view; G, same, tip of dactylus, dorsal view; H, same, tip of fixed finger, dorsal view;I, same, basal part of fingers, dorsal view. Scale bars = 1.0 mm.

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 [bothVarunidae] (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 0.64mm, n = 10) in size, suggesting an amphidromous life cycle.

large individuals relatively more robust than smaller ones
(Figs. 8–12); the carpi of ovigerous females (pocl 20.20mm, QM-W28316; pocl 21.66 mm, ZRC 2015.281) slightly
longer than that in males (carpi 0.61–0.66 of chela length infemales vs. 0.48–0.53 in males); the length of dactylus topalm in smaller males (pocl 16.26 mm, ZRC 2015.282; pocl
13.22 mm, RUMF-ZC-2802) is distinctly shorter than thatin large males (ratio of 1.56–1.75 in smaller males versus
1.21–1.35 in large males) (Figs. 8–12).
Color in life. Whole body (carapace, abdomens, andappendages) generally whitish to pale yellow (Figs. 13, 14).

Distribution. Only known from Christmas Island thus far.

Habitat and biology. Macrobrachium xmas n. sp. wascollected 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 fromChristmas Island caves include: a procaridid Procaris

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 inapposition.
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Fig. 7. Macrobrachium xmas n. sp., holotype male (pocl 18.74 mm) (QM-W28315). Third to fifth pereiopods, lateral view. A, third
pereiopod, lateral view; B, same, posterior part of propodus, lateral view; C, fourth pereiopod, lateral view; D, same, posterior part ofpropodus, lateral view; E, fifth pereiopod, lateral view; F, same, posterior part of propodus, lateral view. Scale bars = 1.0 mm.

Fig. 8. Macrobrachium xmas n. sp., paratype male (pocl 21.75 mm) (OUMNH.ZC.2015-02-048). A, rostrum, carapace, and cephalicappendages, lateral view; B, eye (left side), ventral view; C, left second pereiopod, lateral view; D, right second pereiopod, lateral view;E, same, basal part of fingers, dorsal view. Scale bars = 1.0 mm.

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Fujita et al.: New stygobitic prawn of the genus Macrobrachium
Remarks. Among the 12 stygobitic Macrobrachium
species, it is known that M. gua, and M. lucifugum, havewell developed eyes like their epigean congeners (seeChong, 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 bylacking 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, 8–12; Kemp,
1924; Holthuis, 1977; Mejía-Ortíz et al., 2008). In addition
to these differences, M. cavernicola can be separated fromM. 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), (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), and the carpi of thesecond pereiopods are proportionally shorter (Kemp, 1924:
pl. 3, fig. 1) than in M. xmas (Fig. 6C, F) (0.27–0.34 of thechela length versus about 0.5). In the morphology of thesecond pereiopod, M. acherontium (Holthuis, 1977) and M.
sbordonii (Mejía-Ortíz et al., 2008: figs. 2A, 3E) differ fromM. 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).

6 versus 4 in M. miyakoense) (cf. Figs. 1A, 2A, 4A, 8A,
9A, 10A, 11A, 12A; 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 originallydescribed 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 holotypeof M. microps (cl 22.0 mm) can be easily distinguished fromM. xmas by the slightly shorter rostrum (cf. Fig. 4C, 8A,
9A, 10A, 11A, 12A; Holthuis, 1978: fig. 1a, b), the more
reduced cornea (slightly more than half of the eyestalk widthversus about 0.71–0.78 in M. xmas) (cf. Fig. 4C, J; Holthuis,
1978: fig. 1b), and the remarkably larger and stouter second
pereiopods (cf. Fig. 6C, F; 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 cuttingedges 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 inM. 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; Holthuis, 1978: fig. 1).

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, 8-12;
Holthuis, 1984: fig. 1a), the smooth second pereiopod(Holthuis, 1984: fig. 1e, f) (profusely spinose in M. xmas,
Fig. 6C, F), 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).

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 wasvery brief, the female they described agrees well with oursamples of M. xmas. The young male differs a little inhaving only 4 teeth on the carapace posterior to the dorsal
margin (Short & Meek, 2000: Fig. 2A); and by the second
pereiopods lacking setal pubescence (Short & Meek, 2000:
Fig. 2B). Although we borrowed the available specimensof Macrobrachium from Christmas Island from WAM, thetwo specimens studied by Short & Meek (2000) were notamong 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.

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; Hobbs & Hobbs, 1995: fig. 1a).
Based on the present description of additional adult maleand female specimens of Macrobrachium miyakoense, it
is clear that this species is morphologically very similar toM. xmas. However, M. xmas can be distinguished by the
relatively longer and more slender rostrum (cf. Figs. 1A, 2A,
4A, 9A, 10A, 11A; 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 proportionallymore swollen eye stalk (cf. Figs. 1B, 2B, 4J, 8B, 9B, 10B,
11B, 12B; Komai & Fujita, 2005: fig. 2C), and by having
more teeth on the post-rostral margin of the carapace (5 orThe smallest male (pocl 8.71 mm, ZRC 2015.283) has nosecond pereiopods, but the number of post-rostral teeth ofthe carapace is the same (only 4 teeth) as the “young male”

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Fig. 9. Macrobrachium xmas n. sp., paratype male (pocl 16.26 mm) (ZRC 2015.282). A, rostrum, carapace, and cephalic appendages,
lateral view; B, eye (left side), ventral view (left), dorsal view (right); C, left second pereiopod, lateral view; D, same, basal part of fingers,
dorsal view; E, right second pereiopod, lateral view. Scale bars = 1.0 mm.

Fig. 10. Macrobrachium xmas n. sp., paratype male (pocl 13.22 mm) (RUMF-ZC-2802). A, rostrum, carapace, and cephalic appendages,
lateral view; B, eye (left side), ventral view (left), dorsal view (right); C, right second pereiopod, lateral view; D, left second pereiopod,
lateral view. Scale bars = 1.0 mm.

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Fujita et al.: New stygobitic prawn of the genus Macrobrachium

Fig. 11. Macrobrachium xmas n. sp., paratype ovigerous female (pocl 21.66 mm) (ZRC 2015.281). A, rostrum, carapace, and cephalicappendages, lateral view; B, eye (left side), ventral view (left), dorsal view (right); C, right second pereiopod, lateral view; D, left second
pereiopod, lateral view. Scale bars = 1.0 mm.

Fig. 12. Macrobrachium xmas n. sp., paratype ovigerous female (pocl 20.20 mm) (QM-W28316). A, rostrum, carapace, and cephalicappendages, lateral view; B, eye (left side), ventral view; C, right second pereiopod, lateral view; D, left second pereiopod, lateral view;E, same, basal part of fingers, dorsal view. Scale bars = 1.0 mm.

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Fig. 13. Macrobrachium xmas n. sp., coloration of the live
specimens. A, paratype male (pocl 21.75 mm) (OUMNH.ZC.201502-048), Freshwater Cave; B, C, paratype male (pocl 16.26 mm)(ZRC 2015.282), Runaway Cave (Photographs by: HH Tan).

Fig. 14. Macrobrachium xmas n. sp., coloration of live specimens.
A, paratype ovigerous female (pocl 21.66 mm) (ZRC 2015.281),
Whip Cave; B, C, paratype ovigerous female (pocl 20.20 mm)(QM-W28316), Freshwater Cave (Photographs by: HH Tan).

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 refertheir record of M. microps from Christmas Island to thepresent new species. We also examined 62 juveniles of“Macrobrachium sp.” from Christmas Island (pocl 2.5-12.1
mm: WAM-C44823, C44824, C44825, C44826, C44827,
C44828, C44829, C44830, C44831, C44832, C44833,
C44834, C44835, C44836, C44837, C44839, C44840)
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 notcatch or observe adult M. lar inside the caves (they areotherwise common in epigeal waters in Christmas Island(Ng & Davie, 2012), they have been found in subterraneanwaters 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 bycharacters 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 distinguishedfrom 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 stalkwidth versus 0.71–0.78 in M. xmas) (cf. Figs. 4A, C, J, 8B,
9A-B, 10A, B, 11A, B, 12A, B; Bruce & Iliffe, 1993: figs.
1, 2A–D, H).
Short & Marquet (1998) reported two males (pocl 21.6mm 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-reaching623

Fujita et al.: New stygobitic prawn of the genus Macrobrachiumthe distal end of the antennular peduncle. The description
by Short & Marquet (1998) is too brief, and it is difficult tocompare with M. xmas in detail, however we believe that thematerial 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, 12C, D).

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ACKNOWLEDGEMENTS
We are indebted for the help and encouragement of Max
Orchard, at that time, Senior Ranger of the Christmas Island
Park Service. We thank the Australian National Parks Service
for the various research and export permits to collect, as wellas the substantial logistical support they provided us on theisland. The authors are very grateful to our team members of
Xmas Island Expeditions of 2010–2012 (Tan Heok Hui, Tan
Swee Hee, Tohru Naruse, Joelle Lai, Tan Siong Kiat, Jose
Mendoza and Tan Kai Xin) for their energy and enthusiasm
during the fieldwork. Thanks are also due to Diana Jonesand Andrew Hosie (WAM) for sending us specimens forstudy. We are also grateful to Sammy De Grave for someenthusiastic discussions on the identity of the present species,
and for his help in searching for the types of M. microps. He
and Charles Fransen provided many important suggestions
to help improve the paper. This work has been supported
by travel grants to the Raffles Museum from the Faculty of
Science, National University of Singapore (to PNKL), andwas further supported by Australian Biological Resources
Study Grants no. 208-72, and 207-50 to PJFD.
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