THE RAFFLES BULLETIN OF ZOOLOGY 2012
THE RAFFLES BULLETIN OF ZOOLOGY 2012 60(1): 57–70
Date of Publication: 29 Feb.2012© National University of Singapore

TWO NEW SPECIES OF ORCOVITA (CRUSTACEA: DECAPODA:
BRACHYURA: VARUNIDAE) FROM ANCHIALINE CAVES ON
CHRISTMAS ISLAND, EASTERN INDIAN OCEANPeter J. F. Davie
Queensland Museum, PO Box 3300, South Brisbane, Queensland, Australia
Email: Peter.Davie@qm.qld.gov.au

Peter K. L. Ng
Tropical Marine Science Institute and Raffles Museum of Biodiversity Research
Department of Biological Sciences, National University of Singapore
Kent Ridge, Singapore 119260, Republic of Singapore
Email: dbsngkl@nus.edu.sg

ABSTRACT. — Two new species of anchialine varunid crabs of the genus Orcovita Ng & Tomascik, 1994,
O. orchardorum and O. hicksi, are described from Christmas Island, eastern Indian Ocean. This marks thefirst record of Orcovita from the Indian Ocean. The new species are easily distinguished from congeners bydifferences in the form of the carapace, chelae, ambulatory legs, and male abdomen. Two groups of Orcovita
are recognised, and their affinities discussed. A new key is provided for the 10 known species.
KEY WORDS. — Crustacea, Brachyura, Orcovita, new species, Christmas Island

Bruce & Davie, 2006). Although, no anchialine crabs havebeen previously reported from Christmas Island, our efforts
were immediately rewarded with the discovery of two new
species of Orcovita living sympatrically in the same caves.
This represents the first record of this genus from both theIndian Ocean and Australia. The new species are describedherein.

INTRODUCTION
Species of the varunid genus Orcovita Ng & Tomascik,
1994, are apparently anchialine cave specialists. Thus far,eight species have been described, all from caves in thenorthwestern Pacific region south to the Loyalty Islands,
viz., O. saltatrix Ng & Tomascik, 1994 (Indonesia); O.
angulata Ng, Guinot & Iliffe, 1996 (Philippines); O. fictilia
Ng, Guinot & Iliffe, 1996 (Philippines); O. gracilipes Ng,
Guinot & Iliffe, 1996 (Niue); O. mollitia Ng, Guinot & Iliffe,
1996 (Guam); O. mcneiceae N. K. Ng & Ng, 2002 (Loyalty
Islands), O. miruku Naruse & Tamura, 2006 (Ryukyus,
Japan), and O. holthuisi N. K. Ng & Ng, 2009 (Philippines)(Ng et al., 2008).

Christmas Island is the tip of an isolated seamount rising
4.5 km from the ocean floor in the Wharton Basin of the
Indian Plate. It is part of a chain of volcanoes that formed
from the mid-Cretaceous starting about 80 Ma. It is the only
one to be exposed above sea-level, and was the model forCharles Darwin’s concept of oceanic islands. Grimes (2001)
reviewed what is known of the geomorphology, geology
and genesis of the cave systems on the island. “The basaltic
core of Christmas Island is encased in a series of limestones
dating from the Eocene to the Recent and eustatic changes
have produced a series of marine terraces...near the coast
seawater intrudes beneath the freshwater within the karstic
limestone...so forming an anchialine collar around the island.
The saltwater interface caves are strongly tidal” (Humphreys& Eberhard, 2001: 60).

The present study arose out of collecting trips to explore thedecapod crustacean diversity of Christmas Island in Jan.2010(Xmas Island Expedition 2010) and Mar.2011 (Xmas Island
Expedition 2011). One paper on a new arboreal crab (Ng &Davie, 2011) has already been published, and a new land crab
is described in this volume (Ng & Davie, 2012). Collapsible
bait traps and tubular plastic shrimp and crab traps (of a typecommonly used in Taiwan), were laid in the more accessible
anchialine caves, in the hope of collecting additional materialof the decapod crustaceans previously reported from theisland (Humphreys & Eberhard, 2001; Namiotko et al., 2004;

The term ‘anchialine’ was first coined by Holthuis (1973: 3)
to differentiate ‘pools with no surface connection with the sea,57

Davie & Ng: New Orcovita species from Christmas Island
containing salt or brackish water, which fluctuates with thetides’. For a review of the diversity of anchialine cave fauna,
its ecology, and its origins see Iliffe & Kornicker (2009).

Cave, Waterfall Road, 10°25.377'S, 105°42.081'E, coll. Xmas Island
Expedition 2011, 27 Mar.2011. All localities in Christmas Island.

Description. — Carapace subrectangular (Figs. 1, 4, 5A),
distinctly broader than long (width to length ratio ca. 1.25),
dorsal surface mostly smooth, glabrous, finely punctate,
but becoming finely granular anteriorly and anterolaterally,
especially in females; regions poorly defined except for deepH-shaped gastro-cardiac groove and pair of strong medial
postfrontal lobes; cervical grooves indistinct, shallow, broad;epigastric cristae low, indistinct; low ridge present adjacent
to junction between posterolateral margin and posterior
carapace margin. Anterolateral margin edged with low,
indistinct, rounded granules; not clearly demarcated fromposterolateral margin; exorbital angle very broad; with 2
epibranchial teeth, first tooth prominent, rounded, separated
from exorbital angle by V-shaped cleft, second tooth smaller
and lower; posterolateral margins straight or weakly concave,
clearly converging posteriorly; posterior carapace margin
straight; supraorbital margin granulate, medially moderately
convex, inner margins convergent towards frontal margin;
frontal margin (Fig. 5A) sinuous, with broad shallow medial

The present new species were compared with material of
known Orcovita species as listed in N. K. Ng & Ng (2002,2009). Measurements provided (in millimetres) are of thecarapace width and length, respectively. Measurements ofthe various leg segments follow Ng et al. (1996) and N.
K. Ng & Ng (2002, 2009). The abbreviations M, P, and D
refer to the merus, propodus, and dactylus of the ambulatory
legs, respectively, while the number preceding it refers to
the respective leg; G1 and G2 are used for the male first andsecond pleopods, respectively. Specimens are deposited in
the Queensland Museum, Brisbane (QM); Western AustralianMuseum, Perth (WAM); and the Zoological ReferenceCollection, Raffles Museum of Biodiversity Research,
National University of Singapore, Singapore (ZRC).
In a local Christmas Island newsletter, Anonymous (2011)
reported that the authors, together with their team, haddiscovered the two new species of Orcovita and gave their
proposed scientific names, Orcovita hicksi and Orcovita
orchardorum, as well as a photograph of the latter taxon.
While this publication gave Latin names and etymologies,
it does not provide any diagnosis, description, or indicationof how many specimens there were or their depositories. As
such, both names are nomina nuda.

TAXONOMYFamily VARUNIDAE H. Milne Edwards, 1853
Subfamily VARUNINAE H. Milne Edwards, 1853
Orcovita Ng & Tomascik, 1994
Orcovita orchardorum, new species(Figs. 1, 4, 5, 6A, 6B, 9A, 9B, 10A, 11A–D, 12)Material examined. — Holotype: male (21.0 × 16.7 mm) (QMW29114), station CI-14, Whip Cave, Waterfall Road, 10°25.377'S,
105°42.081'E, coll. Xmas Island Expedition 2010, 27 Jan.2010.
Paratypes: 1 male (15.5 × 12.5 mm), 1 female (18.9 × 15.2 mm)(QM-W29115), same data as holotype — 3 males (23.2 × 18.7 mm,
20.4 × 16.7 mm, 14.2 × 11.9 mm), 3 females (largest 19.9 × 16.3mm, 19.9 × 16.1 mm, 16.7 × 13.5 mm) (ZRC 2012.0062), station
CI-14, Whip Cave, Waterfall Road, 10°25.377'S, 105°42.081'E, coll.
Xmas Island Expedition 2010, 27 Jan.2010 — 2 males, 1 female(ZRC 2012.0063), station CI-17, Runaway Cave, Waterfall Road,
10°25.386'S, 105°42.063'E, coll. Xmas Island Expedition 2010,28 Jan.2010 — 1 male (16.0 × 13.4 mm), 1 ovigerous female(17.3 × 14.3 mm) (ZRC 2012.0064), station CI-18, Whip Cave,
Waterfall Road, 10°25.377'S, 105°42.081'E, coll. Xmas Island
Expedition 2010, 28 Jan.2010 — 1 male (15.4 × 12.9 mm) (ZRC
2011.0065), station CI-26, Whip Cave, Waterfall Road, 10°25.377'S,
105°42.081'E, coll. Xmas Island Expedition 2011, 25 Mar.2011— 1 male (17.3 × 14.4 mm) (QM-W29116), station CI-29, Whip
Cave, Waterfall Road, 10°25.377'S, 105°42.081'E, coll. Xmas
Island Expedition 2011, 26 Mar.2011 — 1 male (QM-W29214),
station CI-30, Freshwater Cave, near The Blowholes, 10.51325°S,
105.62421°E, coll. Xmas Island Expedition 2010, 02 Feb.2010— 1 male (17.6 × 14.4 mm) (QM-W29215), station CI-31, Whip

Fig. 1. Orcovita orchardorum, new species. Colours in life, overall
dorsal views. A, paratype male (23.2 × 18.7 mm) (ZRC 2012.0062),
station CI-14, 2010; B, paratype male (15.4 × 12.9 mm) (ZRC
2011.0065), station CI-26, 2011; C, paratype female (19.9 × 16.3mm) (ZRC 2012.0062), station CI-14, 2010.

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Ambulatory legs somewhat dorsoventrally flattened, allsegments long, slender; second ambulatory leg slightly longer
than third; surface smooth. Meri each with long patch of finesetae over upper third adjacent to carapace, relatively sparseon last leg; anterior margin of merus with blunt subdistal
lobe. Outer surface of carpus smooth, lacking setae; anterior
and posterior margins of propodus with small clumps of longand short setae, respectively; dactylus tapering to slender,
acute tip. Dactyli rectangular in cross section, upper andlower margins fringed with dense short setae; 3M long,
slender (length to width ratio 4.0), 3P long, slender (length
to width ratio 3.8), 3D very long, slender (length to width
ratio 7.5); 4M long, slender (length to width ratio 3.7), 4P
long (length to width ratio 2.6), 4D long, slender (length towidth ratio 5.5).

sinus, low transverse ridge of granules just behind true
frontal margin defining a deflexed narrow anterior medianstrip (Fig. 5B); infraorbital margins incomplete, median lobe
low, convex, coarsely granulate, separated from exorbital
tooth by deep sinus; distinct row of rounded granules below
infraorbital margin on suborbital region, extending to subbranchial region (Fig. 5B). Antennal segments entering orbital
hiatus. Antennules broad; interantennular septum broad.
Eyes well-developed, cornea pigmented. Epistome (Fig.
5B) relatively narrow, posterior margin with 2 lateral clefts,
median part broadly triangular, margin coarsely granulate.
Third maxilliped (Fig. 5B) with broad, stout exopod, exopod
0.9 times as narrow as ischium, flagellum well developed;
ischium stout (length to width ratio ca. 2.0, measured alongouter edge), smooth, outer margin minutely granulate; merus
broad (length to width ratio ca. 1.4), antero-external margin
minutely granular, markedly auriculiform.

Male abdomen narrowly triangular (Fig. 9A); lateral margins
edged with very short, dense setae interspersed with several
long, stiff setae; first abdominal somite widest, slightly wider
that third, weakly arched, with transverse ridge; second
abdominal somite reduced to short strip, slightly narrower

Chelipeds relatively long, surface of segments smooth. Malechelae swollen, subequal; fingers as long as palm; base of
fingers and adjacent areas with long, dense setae (Fig. 6A,B), longer on smaller adult males, without distinct pulvinus.
Merus trihedral, external and posterior margins with low
granules, inner anterior margin armed with row of 8–10
large rounded granules. Carpus rounded, smooth, inner distal
angle with low, obtuse tooth. Female chelae similar to thoseof male but smaller, non-setose.

Fig. 3. Orcovita hicksi, new species. Colours in life, overall dorsal
views. A, paratype male (15.9 × 12.2 mm) (ZRC 2012.0080), station
CI-12, 2011; B, paratype male (14.4 × 11.3 mm) (ZRC 2012.0073),
station CI-14, 2010; C, paratype female (20.8 × 15.9 mm) (ZRC
2012.0073), station CI-14, 2010.

Fig. 2. Orcovita hicksi, new species. Colours in life, paratypemale (23.5 × 17.3 mm) (ZRC 2012.0076), station CI-14, 2011. A,
overall dorsal view; B, frontal view of carapace; C, outer view ofleft chela.

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Davie & Ng: New Orcovita species from Christmas Islandthan third; third abdominal somite broad, weakly convex
laterally; fourth abdominal somite broader but shorter thanfifth abdominal somite; fifth abdominal somite with proximaland distal margins moderately sinuous, lateral margins
convergent; sixth abdominal somite rectangular 1.9 times
wider than long, lateral margins weakly convex distally,
proximal margin straight; telson slightly longer than wide(ca. 1.1 times), lateral margins subparallel, broadly roundeddistally. Female abdomen very broad, covering most ofthoracic sternum (Fig. 9B).

broader. G1 (Fig. 11A–C) slender, weakly curving outwards,
reaching to or slightly beyond anterior margin of sternite
5; terminal lobe elongate; genital opening lateral to baseof apical corneous section; subterminal lobe pectinated,elongate, densely setose. G2 short, small (Fig. 11D). Vulva
raised, convex, oval.

Male thoracic sternum (Fig. 9A) generally smooth, punctate;lateral margins of first 2 thoracic sternites armed with largesmooth granules; triangular part of sternites 1 and 2 withpatch of long dark setae inside medial excavation; suture
between sternites 2 and 3 slightly convex antero-medially;
lateral margins of sternites 3 and 4 sinuous, with deep, broad
notch and granulate lobe, indicating edge of fused suture;
deep narrow median longitudinal groove between sternites 7
and 8. Female thoracic sternum similar in form but relatively

Etymology. — Named for Max and Beverley Orchard. As
Head Ranger on Christmas Island for 18 years, and continuing
on as Project Officer, Max, with the wonderful support of hiswife Bev, have worked tirelessly for the conservation of thebiota of Christmas Island. In particular Max, has spearheaded
the control of the Yellow Crazy Ant (Anoplolepis gracilipes),which has had a devastating effect on the crab populationsof the island. Without people who care, like Max and Bev,
the world would be a much poorer place!

Colour. — In life, the colour was an orangish-yellow to paleyellowish-white, with branchial regions paler; setae on thechela were dark brown (Fig. 1).

Fig. 4. Orcovita orchardorum, new species, dorsal view. A, holotype male (21.0 × 16.7 mm) (QM-W29114); B, paratype female (18.9 ×
15.2 mm) (QM-W29115).

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Orcovita orchardorum, new species, can also be easily
separated from its fellow islander, O. hicksi, new species, by
having two epibranchial teeth instead of only one (Figs. 1,
4, 5A versus Figs. 2A, 3, 7, 8A); relatively prominent postfrontal lobes compared with post-frontal lobes obsolete (Figs.
1, 4, 5A versus Figs. 2A, 3, 7, 8A); relatively shorter, stockier
legs versus longer more slender legs (Figs. 1, 4 versus Figs.
Figs. 2A, 3, 7); and a distinct thick patch of long setae atthe base of the gape of the male chela that extends onto thefingers, a feature that is lacking in O. hicksi, new species (Fig.
6A, 6B versus Figs. 2C, 6C, 6D). In addition, the deflexed
portion of the front above the interantennular septum is anarrow strip in O. orchardorum, new species, but is relatively
wider in O. hicksi, new species (Fig. 5B versus Figs. 2B,
8B). Finally, the sixth abdominal somite is proportionately
narrower in O. orchardorum, new species (1.9 times wider
than long versus 2.2 times) (Fig. 9A versus Fig. 9C).

Remarks. — Orcovita orchardorum, new species, mostresembles O. holthuisi from Coron Island, the Philippines,
and O. miruku from the Ryukyus, Japan.
In O. holthuisi, the anterolateral teeth are both acute (cf. N.
K. Ng & Ng, 2009: Figs. 1, 3A), whereas in O. orchardorum,
new species, the second tooth is more in the form of a broadlobe without a deep notch (Figs. 1, 4, 5A); the sixth maleabdominal somite about 2.3 times wider than long (cf. N. K.
Ng & Ng, 2009: Fig. 3K) versus 1.9 times in O. orchardorum,
new species (Fig. 9A); and the male telson 1.5 times thelength of the sixth abdominal somite (cf. N. K. Ng & Ng,
2009: Fig. 3K) versus ca. 1.1 times in O. orchardorum, newspecies (Figs. 9A). Their leg proportions (P4 & P5) also
differ, as summarised in Table 2.
In O. miruku, the anterolateral teeth are similarly broadly
rounded but both are clearly defined and similar inprominence (cf. Naruse & Tamura, 2006: Figs. 1, 2a), whereasin O. orchardorum, new species, the first anterolateral tooth isdeeply notched and prominently projecting, while the second
is smaller and less strongly defined by a deep notch (Figs. 1,
4, 5A). Also in O. miruku, the male telson is slightly longer,
1.2 times length of sixth abdominal somite (cf. Naruse &Tamura, 2006: Fig. 2g) versus 1.1 times in O. orchardorum,
new species (Fig. 9A).

Habitat. — Orcovita orchardorum, new species, and O.
hicksi, new species, are relatively abundant in Whip andRunaway Caves that are about 50 m apart from each otherabove ground and almost certainly have a subterraneanconnection. Both caves are tidally and freshwater influenced
brackish anchialine habitats. Orcovita hicksi, new species,
has also been collected 19th Hole Cave, which is only a few
kilometres away. Both species were found from Freshwater
Cave, near The Blowholes a site much further south. As
these animals clearly have a marine dispersal phase, this is
not surprising. We only managed to collect one ovigerous
female (17.3 × 14.3 mm, ZRC) from Whip Cave but we could
not get the eggs to hatch. The eggs are small and numerous,
and typical of varunids.
Both new species of Orcovita were collected with otherdecapods including the alpheid shrimp Metabetaeus minutus(Whitelegge, 1897) (see Anker, 2010), a possible new speciesof hippolytid shrimp, Parahippolyte sp., a new speciesof Macrobrachium (Palaemonidae), and an atyid shrimp
Antecaridina (?) lauensis (Edmondson, 1935).
Besides these, numerous other aquatic species have alreadybeen previously reported within the same wider cave systems
including: an unidentified Scyllidae sp. (Polychaeta); Nerillasp. (Archiannelida: Nerillidae); Microceratina martensi(Ostracoda: Cytheruridae); Danielopolina baltanasi(Thaumatocyprididae: Halocyprida) (Humphreys &Danielopol, 2006; Humphreys et al., 2009); Nitocrella/Nitokra
complex (Harpacticoida: Ameiridae); Bryocyclops muscicola(Menzel)(Cyclopoida: Cyclopinidae); a new copepod genus(Calanoida: Arietellidae); Leucothoe sp. (Amphipoda:
Leucothoidae); Macrobrachium lar (Fabricius)(Decapoda:
Palaemonidae); Gobioidae indet. (Pisces: Perciformes);
unidentified Eleotridae (Pisces: Perciformes) (see Humphreys& Eberhard, 2001; Namiotko et al., 2004); Eleotris (?) fusca(Eleotridae) (Humphreys & Eberhard, 2001; Namiotko et al.,2004). Three species of eels (Anguilla bicolor, Anguillidae),Echidna sp. (Muraenidae), and an unidentified muraenesocidwere also present in Whip and Runaway Caves (H. H. Tan,pers. comm.).

Fig. 5. Orcovita orchardorum, new species, holotype male (21.0 ×
16.7 mm) (QM-W29114). A, carapace; B, frontal view.

61Davie & Ng: New Orcovita species from Christmas Island
Table 1. Physical and chemical parameters of groundwaters from Runaway Cave and from an adjacent cave in the same anchialine system
where the new Orcovita species were found. Measurements were taken on 5–6 Apr.1998. Data reproduced from Namiotko et al. (2004).
Cave

Dissolved oxygen

Runaway Cave (CI-2)
The 19th Hole (CI-19)(mg dm–3)%

Conductivity(mS cm–1)

Temperature
(°C)

pH

surface

7.06

97.7

5.5

26.9

7.99

2 m depth

6.67

96.6

8.1

26.5

7.50

surface

6.60

94.0

31.2

27.0

7.60

2 m depth

5.05

73.0

34.4

27.4

7.35

In general, according to Humphreys & Eberhard (2001),
the cave waters are all well oxygenated (dissolved oxygen>73% saturated) and the pH (7.65±0.41, N =13), with themarine caves having salinities ranging from 0.39–16.5 g L–1
TDS (sea water c. 36 g L–1 TDS). Specific physico-chemicalmeasurements for Runaway Cave, and the nearby 19th HoleCave, are presented in Table 1. Runaway Cave is brackishwith salinities ranging from about 9–18 ppt. No measurements
deeper than 2 m were taken so it is not known if deeper waters
become suboxic as reported for many other anchialine systems(see Sket, 1996; Humphreys, 1999; Iliffe, 2000).

105°42.081'E, Xmas Island Expedition 2010 — 1 male (14.4 × 11.3mm), 2 females (larger 20.8 × 15.9 mm) (ZRC 2012.0073), station
CI-14, Whip Cave, Waterfall Road, 10°25.377'S, 105°42.081'E, coll.
Xmas Island Expedition 2010, 27 Jan.2010 — 1 male, 1 female(QM-W29118), station CI-15, Runaway Cave, Waterfall Road,
10°25.386'S, 105°42.063'E, coll. Xmas Island Expedition 2010,27 Jan.2011 — 2 females (QM-W29119), station CI-17, Runaway
Cave, Waterfall Road, 10°25.386'S, 105°42.063'E, coll. Xmas Island
Expedition 2010, 28 Jan.2010 — 1 male (ZRC 2012.0074), station
CI-18, Whip Cave, Waterfall Road, 10°25.377'S, 105°42.081'E,
coll. Xmas Island Expedition 2010, 28 Jan.2010 — 1 male (16.4 ×
13.8 mm) (ZRC 2012.0075), station CI-30, Whip Cave, Waterfall
Road, 10°25.377'S, 105°42.081'E, coll. Xmas Island Expedition
2010, 02 Feb.2010 — 1 male (23.5 × 17.3 mm) (ZRC 2012.0076),
station CI-10, Freshwater Cave, near The Blowholes, 10.51325°S,
105.62421°E, coll. Xmas Island Expedition 2011, 22 Mar.2011— 3 females (ZRC 2011.0077), station CI-10, Freshwater Cave,near The Blowholes, 10.51325°S, 105.62421°E, coll. Xmas Island
Expedition 2011, 22 Mar.2011 — 2 females (ZRC 2011.0079),
station CI-12, 19th Hole Cave, next to Christmas Island Golf Course,
10.42488°S, 105.70123°E, 19th Hole, near Golf Course, coll. Xmas
Island Expedition 2011, 22 Mar.2011 — 1 male (15.9 × 12.2 mm)(ZRC 2012.0080), station CI-12, 19th Hole Cave, next to Christmas
Island Golf Course, 10.42488°S, 105.70123°E, coll. Xmas Island

Orcovita hicksi, new species(Figs. 2, 3, 6C, 6D, 7, 8, 9C–E, 10B, 11E–I, 12)Material examined. — Holotype: male (17.4 × 13.2 mm) (WAMC49450), field no. BES14437, Whip Cave, Waterfall Road,
Christmas Island, 10°25'22.0"S, 105°42'04.4"E, coll. R Anderson, 8
May 2006 — Paratypes: 1 female (14.2 × 10.8 mm) (WAM-C49451),
same data as holotype — 1 immature female (15.2 × 11.9 mm) (QMW29117), station CI-14, Whip Cave, Waterfall Road, 10°25.377'S,

Fig. 6. Male left and right chelae. A, B, Orcovita orchardorum, new species, holotype male (21.0 × 16.7 mm) (QM-W29114). C, D, Orcovita
hicksi, new species, holotype male (17.4 × 13.2 mm) (WAM-C49450).

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Description. — Carapace subrectangular to subovate (Figs.
2A, 3, 7, 8A), distinctly broader than long (width to length
ratio ca. 1.25), dorsal surface mostly smooth, glabrous,
finely punctate, but becoming finely granular anteriorly andanterolaterally, especially in females; regions mostly poorly
defined, gastro-cardiac groove deeply grooved laterally;
postfrontal lobes obsolete; cervical grooves indistinct,
shallow, broad; epigastric cristae low, indistinct; short, lowridge present adjacent to junction between posterolateral
margin and posterior carapace margin. Anterolateral margin
lined with distinct, rounded granules; not clearly demarcatedfrom posterolateral margin; exorbital angle very broad,separated from single epibranchial tooth by rounded sulcus;
posterolateral margins straight or weakly concave, clearly
converging posteriorly; posterior carapace margin straight;

Expedition 2011, 22 Mar.2011 — 5 males (largest 21.2 × 15.9mm) (ZRC 2012.0066), station CI-14, Freshwater Cave, near The
Blowholes, 10.51325°S, 105.62421°E, coll. Xmas Island Expedition
2011, 23 Mar.2011 — 4 males (largest 19.7 × 15.3 mm), 1 female(18.3 × 14.3 mm) (QM-W29218), station CI-19, Runaway Cave,
Waterfall Road, 10°25.386'S, 105°42.063'E, coll. Xmas Island
Expedition 2011, 24 Mar.2011 — 1 male, 1 female (QM-W29225),
station CI-35, Freshwater Cave, near The Blowholes, 10.51325°S,
105.62421°E, coll. Xmas Island Expedition 2011, 28 Mar.2011 — 1
male (16.3 ×12.5 mm), 1 female (19.9 × 14.8 mm) (WAM-C49452),
field no. BES11648, Whip Cave, 10°25.377'S, 105°42.081'E, coll.
R. D. Brooks, 19 Jun.2004 — 1 male (15.0 × 11.4 mm) (WAMC49453), field no. BES14439, 19th Hole Cave, next to Christmas
Is. Golf Course, 10°25'30.0"S, 105°42'04.2"E, coll. R Anderson,
19 May 2006. All localities in Christmas Island.

Fig. 7. Orcovita hicksi, new species, dorsal view. A, holotype male (17.4 × 13.2 mm) (WAM-C49450); B, paratype female (15.2 × 11.9mm) (QM-W29117).

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Davie & Ng: New Orcovita species from Christmas Island
supraorbital margin granulate, medially moderately convex,
inner margins obliquely convergent towards frontal margin;
frontal margin dorsally (Fig. 8A, B) appearing broadly
concave, defined by transverse ridge of granules; true
frontal margin almost vertically deflexed, sinuous, concave
medially, separated from dorsal granular ridge by relatively
wide strip tapering laterally; infraorbital margins incomplete,
median lobe low, convex, coarsely granulate, separated fromexorbital tooth by deep sinus; strong row of rounded granules
below infraorbital margin on suborbital region, extending to
sub-branchial region (Fig. 8B). Antennal segments entering
orbital hiatus. Antennules broad; interantennular septum
broad. Eyes well-developed, cornea pigmented. Epistome(Figs. 8B, 10B) relatively narrow, posterior margin with 2
lateral clefts, median part broadly triangular, margin finely
granular. Third maxilliped (Figs. 8B, 10B) with broad,stout exopod, exopod 0.9 times width of ischium, flagellum
well developed; ischium stout (length to width ratio ca.
1.9, measured along outer edge), surface smooth, bearing
scattered very short setae, outer margin minutely granulate;merus broad (length to width ratio ca. 1.4), antero-external
margin minutely granular, markedly auriculiform.

Ambulatory legs somewhat dorsoventrally flattened, allsegments long, slender; second and third ambulatory legs
equal longest; upper and lower surfaces mostly smooth.
Meri with upper and lower borders finely serrated; proximal
upper surface granular; anterior margin of merus with blunt
subdistal lobe. Outer surface of carpus smooth, lacking setae;
anterior and posterior margins of propodus with small clumpsof long and short setae, respectively; dactylus tapering toslender, acute tip. Dactyli rectangular in cross section, upperand lower margins fringed with dense short setae; 3M long,
slender (length to width ratio 5.6), 3P long, slender (length
to width ratio 4.8), 3D very long, slender (length to width
ratio 11.0); 4M long, slender (length to width ratio 4.5), 4P
long (length to width ratio 2.4), 4D long, slender (length towidth ratio 6.4).
Male abdomen narrowly triangular (Fig. 9C); lateral margins
edged with very short, dense setae interspersed with several
long, stiff setae; first abdominal somite widest, slightly wider
that third, weakly arched, with transverse ridge; second
abdominal somite reduced to short strip, slightly narrower
than third; third abdominal somite broad, weakly convex
laterally; fourth abdominal somite broader but shorter thanfifth abdominal somite; fifth abdominal somite with proximaland distal margins straight, lateral margins convergent; sixth
abdominal somite rectangular 2.2 times wider than long,lateral margins weakly convex distally, proximal margin
straight; telson about as long as wide, lateral margins
subparallel, broadly rounded distally. Female abdomen verybroad, covering most of thoracic sternum (Fig. 9D).

Chelipeds relatively long, surface of segments smooth.
Male chelae swollen, subequal; surface very finely granular;
fingers as long as palm; with a small but distinct pulvinus
at base of fingers, some very short setae around pulvinus
but otherwise naked (Fig. 6C, D). Merus sharply trihedral,
upper inner margin finely granulate, ventral margins morecoarsely granular. Carpus rounded, smooth, inner distal
angle finely dentate. Female chelae similar to those of malebut smaller.

Male thoracic sternum (Fig. 9C) generally smooth, punctate;lateral margins of first 2 thoracic sternites armed with largesmooth granules; triangular part of sternites 1 and 2 withpatch of long dark setae inside medial excavation; suture
between sternites 2 and 3 relatively straight; lateral margins
of sternites 3 and 4 sinuous, with deep, broad notch andgranulate lobe, indicating edge of fused suture; deep narrow
median longitudinal groove between sternites 7 and 8. Female
thoracic sternum similar in form but relatively broader. G1(Fig. 11E–H) slender, weakly curving outwards, reaching toanterior margin of sternite 5; terminal lobe elongate; genital
opening lateral to base of terminal lobe; subterminal lobepectinated, elongate, densely setose. G2 short, small (Fig.
11I). Vulva raised, convex, oval (Fig. 9E).
Colour. — Smaller specimens (up to ca. 16 mm in carapace
width) tend to be yellowish-white to orange (Fig. 3A, B).
When they exceed this size, both males and females become
more whitish, and the anterior half of the carapace is covered
with scattered brown spots and blotches (Figs. 2A, 2B, 3C).
The chela also becomes almost white (Fig. 2C).
Etymology. — Named for John Hicks who was the AustralianGovernment Conservator on Christmas Island from 1979
to 1983. His book “Christmas Crabs”, written with the late
Holger Rumpff and Hugh Yorkston, did much to publicise thisunique crab fauna to the eyes of the world, and could only
have been written by one who was as thoroughly entrancedby the Christmas Crabs, as we are ourselves.

Fig. 8. Orcovita hicksi, new species, holotype male (17.4 × 13.2mm) (WAM-C49450). A, carapace; B, frontal view.

64THE RAFFLES BULLETIN OF ZOOLOGY 2012
Remarks. — Orcovita hicksi, new species, can easily beseparated from O. orchardorum, new species, and its close
allies O. miruku and O. holthuisi, by its single epibranchial
tooth (vs. two epibranchial teeth present in the latter species)
and the absence of a tuft of setae at the base of cheliped fingers
in males (vs. present in the latter three species) (see Remarks

for O. orchardorum, new species). It can be separated fromits closest long-legged relatives (see discussion of Groups I
and II later) by the new key presented here.
Habitat. — See comments for Orcovita orchardorum, newspecies.

Fig. 9. Sternal view showing male and female abdomens. Orcovita orchardorum, new species: A, holotype male (21.0 × 16.7 mm) (QMW29114); B, paratype female (18.9 × 15.2 mm) (QM-W29115). Orcovita hicksi, new species: C, holotype male (17.4 × 13.2 mm) (WAMC49450); D, E, paratype female (20.8 × 15.9 mm) (ZRC 2012.0073), station CI-14, 2010.

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Davie & Ng: New Orcovita species from Christmas Island
2. Junction between antero- and posterolateral margins rounded;
posterolateral margin smooth; lengths of 3P and 4P propodus
4.3 and 3. 1 times width, respectively, lengths of 3D and 4D
7.8 and 5.5 times width, respectively (Kakaban: Indonesia) ..
............................................................................... O. saltatrix– Junction between antero- and posterolateral margins angular;
posterolateral margin granulated; lengths of 3P and 4P 5.4 and3.7 times width, respectively, lengths of 3D and 4D 16.1 and6.6 times width, respectively (Coron: Philippines) .................
.............................................................................. O. angulata
3. Male chela with thick patch of setae at base of gape;
exorbital tooth always clearly separated from rest ofanterolateral margin by deep, distinct cleft, margin never entire……………………………………………… 4– Male chela without an obvious thick patch of setae at base ofgape (at most some sparse short setae along edge; exorbital
tooth separated from rest of anterolateral margin by small cleft,sometimes absent, with margin appearing almost entire ...... 8
4. Anterolateral margins with 2 teeth behind exorbital angle (second
may be reduced to only a broad lobe) .................................. 5– Anterolateral margins with only a single distinct tooth behind
exorbital angle (Loyalty Islands) ...................... O. mcneiceae
5. Carapace relatively broad (ca. 1.4 times wider than long);
ambulatory legs relatively longer, more slender (4M ca. 5.7
times longer than wide) (Niue) ......................... O. gracilipes– Carapace narrower (ca. 1.2 times wider than long); ambulatory
legs relatively shorter (4M ≤4.3 times longer than wide) .... 6
6. Anterolateral teeth both acute; ambulatory legs relatively short,stout (4M 3.9 times longer than wide); sixth male abdominal
somite about 2.3 times wider than long; male telson 1.5 times
length of sixth abdominal somite ........................ O. holthuisi– Anterolateral teeth broadly rounded; ambulatory leg proportions
not as above; sixth male abdominal somite about twice as wide
as long; male telson 1.1-1.2 times length of sixth abdominal
somite .................................................................................... 7
7. Anterolateral teeth both clearly defined, similar in prominence(Ryukyus: Japan) .................................................... O. miruku– First anterolateral teeth deeply notched, prominently projecting,second tooth in form of broad lobe, not defined by distinct notch(Christmas Is.) ......................... O. orchardorum, new species
8. Ambulatory legs relatively long, slender, length of 3P about 5
times width or more .............................................................. 9– Ambulatory legs relatively shorter, length of 3P 4.2 times width,
lengths of 3D and 4D 9.1 and 6.2-6 .9 times width, respectively(Panglao: Philippines) ............................................. O. fictilia
9. Supraorbital margin relatively straight, without distinct lateralconcavity such that exorbital tooth low, not appearing markedly
produced; anterolateral tooth of carapace marked by only
indistinct notch, or obsolete; length of 3P 5.2 times width,
lengths of 3D and 4D 12.9 and 7.6 times width, respectively;
small species (< 15 mm c.b.) (Guam) .................. O. mollitia– Supraorbital margin sinuous, markedly concave laterally suchthat exorbital tooth appears more prominently produced; single
anterolateral tooth of carapace marked by strong V-shaped
notch; length of 3P 4.8 times width, lengths of 3D and 4D 11.0
and 6.4 times width, respectively; larger species (>15 mm c.b.)(Christmas Is.) ..................................... O. hicksi, new species

GENERAL DISCUSSION
Orcovita Ng & Tomascik, 1994, has been described anddiscussed in detail by Ng & Tomascik (1994), Ng et al.
(1996), N. K. Ng & Ng (2002, 2009), and Naruse & Tamura(2006). As previously discussed, the genus currently has 10
species.
The two new species described here are likely to be indigenous
to Christmas Island, as this narrow range endemicity seems
to be the pattern for each of the other Orcovita species. All
species can be separated from each other using the new key
provided.

KEY TO THE GENUS ORCOVITA
1. Carapace appearing distinctly rectangular; posterolateral margins
almost straight, subparallel, not distinctly convergent towards
posterior carapace margin ..................................................... 2– Carapace appearing more hexagonal; posterolateral margins
concave, distinctly convergent towards posterior carapace
margin .................................................................................... 3

The present collection is remarkable in recording two
species living sympatrically in the same caves. The only
similar but not identical situation is with O. holthuisi and O.
angulata both reported from Coron Island in the Philippines,
although at different sites. In that instance it is not known
if the separate caves in which those species each live haveany subterranean connection, and/or if the species occur
together in the same location. The presence of more than one

Fig. 10. Frontal view showing epistome, frontal and anterolateral
margins and orbital and suborbital margins. A, Orcovita orchardorum,
new species, holotype male (21.0 × 16.7 mm) (QM-W29114). B,
Orcovita hicksi, new species, holotype male (17.4 × 13.2 mm)(WAM-C49450).

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THE RAFFLES BULLETIN OF ZOOLOGY 2012
stygobitic species of the same genus in the same cave is not
unprecedented in other groups. In brachyurans, two speciesof freshwater potamids (Cerberusa) have been found in the
Mulu Caves in Sarawak, Borneo (Holthuis, 1979) while two
species of sesarmids (Karstarma) occur in the same cave inBali, Indonesia (Ng, 2002; Davie & Ng, 2007). Three new
species of the remipede, Speleonectes have been describedfrom one underwater room in a cave in the Bahamas (seeKoenemann et al., 2003). Likewise, two stygobitic species of
the halocyprid ostracode, Danielopolina, have been describedfrom an anchialine lava tube cave in the Canary Islands (seeDanielopol et al., 2000).

extends onto the fingers. It includes three species: O. miruku
Naruse & Tamura, 2006, O. holthuisi Ng & Ng, 2009, andO. orchardorum, new species.
Species in Group II have a single epibranchial tooth; lackobviously raised post-frontal lobes; have relatively longer
and more slender legs, and mostly lack a prominent patch ofsetae on the chelae (with the exception of O. gracilipes andO. mcneiceae). It includes seven species: O. saltatrix Ng &Tomascik, 1994, O. angulata Ng, Guinot & Iliffe, 1996; O.
gracilipes Ng, Guinot & Iliffe, 1996; O. fictilia Ng, Guinot& Iliffe, 1996, O. mollitia Ng, Guinot & Iliffe, 1996; O.
mcneiceae Ng & Ng, 2002, and O. hicksi, new species.

We have re-examined the morphology of all 10 speciesof Orcovita, and it is now apparent that on the basis of
the morphology, there are two separate species-groups
that may represent distinct lineages. Species in Group I
typically have two epibranchial teeth; relatively prominent
post-frontal lobes; shorter, stockier legs (for proportions oflast two pereiopods, see Table 2); and a distinct thick patchof long setae at the base of the gape of the male chela that

Interestingly, in both cases where two separate species occur(or are believed to occur) sympatrically (O. holthuisi and O.
angulata from Coron Island, the Phillipines; O. orchardorum,
new species, and O. hicksi, new species, from Christmas
Island), there is, in each case, a representative of each of
the two lineages. This is further good evidence that there
is likely to be a deep-rooted ecological/phylogenetic split

Fig. 11. Male gonopods (denuded). Orcovita orchardorum, new species, holotype male (21.0 × 16.7 mm), (QM-W29114): A–C, abdominaland sternal views of G1, D, G2; Orcovita hicksi, new species, holotype male (17.4 × 13.2 mm) (WAM-C49450): E–H, abdominal andsternal views of G1, I, G2.

67

Davie & Ng: New Orcovita species from Christmas Island
Table 2. Length to width ratios of various ambulatory leg segments of Orcovita species (adapted from Ng & Ng, 2002, 2009; Naruse &Tamura, 2006). 3M, 3P, 3D = third ambulatory leg merus, propodus and dactylus, respectively; and similarly for the fourth leg.
Group IGroup II

3M

3P

3D

4M

4P

4D

O. miruku

4.1

3.7

9.3

3.7*

2.6

6.3

O. holthuisi

4.3

3.9

8.1

3.9

2.7

2.2

O. orchardorum

4.0

3.8

7.5

3.7

2.6

5.5

O. angulata

5.4

5.4

16.1

4.6

3.7

6.6

O. fictilia

5.3

4.2

9.1

4.2–4.4

2.6–3.0

6.2–6.9

O. gracilipes

5.7

5.1

10.8

4.7

3.2

5.9

O. mcneiceae

5.2

5.4

9.8

5.2

3.2

4.9

O. mollitia

5.7

5.2

12.9

4.2–4.7

2.8–3.2

7.6

O. saltatrix

5.8

4.3

7.8

4.4

3.1

5.5

O. hicksi

5.6

4.8

11

4.5

2.4

6.4

*This ratio has been previously given as 6.1 for O. miruku but was a mistake in the original manuscript – Tohru Naruse (pers. comm.) has
checked the holotype and the correct ratio is 3.7.

that has allowed species from both lineages to co-occur.
A DNA study would be ideal to investigate the veracity ofthis hypothesis, to possibly get an indication of the age ofthe genus, and perhaps some correlation with the historicalbiogeography of the region.

(1989) proposed that the mid-oceanic ridge islands may
form a continuous route of dispersal around the globe, but
as Humphreys & Eberhard (2001) have pointed out, there
is no simple connection between the crevicular system of
mid-oceanic ridges and hot spot islands such as Christmas
Island. Thus the restriction of Procaris and Orcovita species toanchialine systems is a strong indication that they are relictual(sensu Humphreys, 2000; Humphreys et al., 2009), and thatthe species on Christmas Island have survived by using thekarst system as a refugium. Kensley & Williams (1986) havealready suggested this concept to explain the occurrence of
decapod procaridids in other anchialine systems. The various
biogeographic models that have been proposed have beenreviewed by Iliffe & Kornicker (2009), but it seems that there
is no simple unified explanation at this time. Our knowledge ofsubterranean or submarine karst systems remains sparse; withmany such systems still poorly surveyed or even unstudied.
The discovery of two new species of Orcovita in Christmas
Island in this study is a case in point.

Biogeography. — The distribution of all 10 species of
Orcovita currently known is presented in Fig. 10. It isdifficult to understand the biogeography of specialisedanchialine genera. Typically isolation appears to have led to
speciation, but this also implies that there must have beensome connectivity of such limestone cave systems in thepast. A similar pattern appears for the family Procarididae,
an aberrant group of shrimps restricted to anchialine cavesin both the Atlantic and Indo-Pacific Oceans. Like Orcovita,
the first record of this family for the Indian Ocean, Procaris
noelensis, was only made recently from the same limestone
caves on Christmas Island (Bruce & Davie, 2006). Hart etal. (1985) and Maciolek (1983) have speculated that the
distribution of Procaris could be much more extensive
than currently known, with gene flow over great distances
occurring via semi-continuous populations distributed
among shallow submerged ‘crevicular’ habitats. Boxshall

ACKNOWLEDGEMENTS
This study would never have taken place but for the passion,
enthusiasm and encouragement of Max Orchard of theChristmas Island Park Service. His help was paramount tothe success of our work. We thank the Australian National
Parks Service for the various research and export permits
to collect, as well as the substantial logistical support they
provided us on the island. The authors are very grateful to
our team members of Xmas Island Expedition 2010 and 2011
(Tan Heok Hui, Tan Swee Hee, Tohru Naruse, Yoshihisa
Fujita, Joelle Lai, Tan Siong Kiat, and Tan Kai Xin) for
their energy and enthusiasm during the fieldwork. We areespecially grateful to Tan Kai Xin and Tan Siong Kiat who
made many of the cave collections, and whose nimblenessand energy helped obtain the material. We also thank Bill
Humphreys and Andrew Hosie of the Western AustralianMuseum, Perth, for providing supplementary material forstudy. Tohru Naruse and Darren Yeo kindly helped us read andcomment on the manuscript. This work has been supported

Fig. 12. Map showing the distributions of the 10 known Orcovita
species.

68THE RAFFLES BULLETIN OF ZOOLOGY 2012by 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.

Humphreys, W. F. & S. Eberhard, 2001. Subterranean fauna of
Christmas Island. Helictite, 37(2): 59–74.

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