THE RAFFLES BULLETIN OF ZOOLOGY 2007
THE RAFFLES BULLETIN OF ZOOLOGY 2007 Supplement No. 16: 67–74
Date of Publication: 31 Dec.2007© National University of Singapore

PLEISTACANTHA ORI, A NEW SPECIES OF DEEP-WATER SPIDER CRAB
(CRUSTACEA: DECAPODA: BRACHYURA: MAJIDAE)
FROM THE WESTERN INDIAN OCEAN
Shane T. Ahyong
Marine Biodiversity and Biosecurity, NIWA, Private Bag 14901, Kilbirnie, Wellington, New Zealand
Email: s.ahyong@niwa.co.nz (Corresponding author)

Peter K. L. Ng
Department of Biological Sciences, National University of Singapore,
14 Science Drive 4, Singapore 117543, Republic of Singapore
Email: dbsngkl@nus.edu.sg

ABSTRACT. – A new species of deepwater spider crab, Pleistacantha ori, is described from the South Western
Indian Ocean. The new species ranges from South Africa to Madagascar and has previously been confusedwith P. moseleyi (Miers, 1886) and P. pungens (Wood Mason & Alcock, 1891), which it most closely resembles.
Pleistacantha ori is the largest known species of the genus, attaining a postrostral carapace length of at least
129.1 mm.
KEY WORDS. – Crustacea, Decapoda, Majidae, Pleistacantha ori, new species, South Africa, Indian Ocean,taxonomy.

INTRODUCTION

with the South African species. The new species, named
Pleistacantha ori, is described below.

A large species of spider crab of the genus Pleistacantha fromthe deep, outer shelf waters of Eastern Africa has been
identified with P. moseleyi (Miers, 1886) by most studentsof the fauna (see Stebbing, 1923; Barnard, 1950; Grindley,1961; Gordon, 1963; Berry & Hartnoll, 1970; Kensley, 1981).
Recently, through the kindness of Sean Fennessy of theOceanographic Research Institute (ORI), Durban, we obtained
a good series of specimens of this large Pleistacantha fromSouth Africa.

MATERIALS AND METHODS
Measurements of specimens are given in millimetres (mm).
Carapace length (cl) includes the rostrum. Postrostral carapace
length (pcl) is measured along the midline from the posterior
carapace margin to the base of the sinus between the rostralspines. Carapace width (cw) is the greatest width and excludes
spines. Pereopods 1–5 are abbreviated P1–5 respectively. The
first male pleopod (gonopod 1) is abbreviated as G1. For
convenience, terminology follows Griffin & Tranter (1986)
in use of the terms rostral spines and interantennular spines,
respectively for the pair of anteriorly directed anterior
carapace spines and the ventrally directed spine separating
the antennular sinuses. Guinot & Richer de Forges (1982)
use the terms pseudorostral spines and rostral spines for what
we term rostral and interantennular spines. Specimens aredeposited in the Raffles Museum of Biodiversity Research,
National University of Singapore (ZRC); Australian Museum,
Sydney (AM); and Muséum national d’Histoire naturelle,
Paris (MNHN).

The South African specimens proved to be an undescribedspecies resembling P. pungens (Wood Mason & Alcock,1891) (type locality Andaman Sea) and P. moseleyi (Miers)(type locality the Philippines). Indeed, Doflein (1904)
synonymised P. pungens and P. moseleyi, a synonymy
accepted by all subsequent authors until Guinot & Richer deForges (1982) tentatively resurrected the former species on
the basis of three specimens from Madagascar. Though we
concur with Guinot & Richer de Forges (1982) that P.
pungens is a valid species, their Malagasy specimens do not
represent P. pungens sensu stricto, but are also identifiable67

Ahyong & Ng: New Pleistacantha from South Africa
TAXONOMY

proximal 2 close together, distalmost beyond midlength ofrostral spine. Orbital margin with 5 or 6 well-spaced spines
increasing in size posteriorly: 1 or 2 small preorbital spines
at level of rostral base, larger supraorbital, slender intercalated
and postorbital spines. Hepatic spine large, anteriorly directed,
with 2 or 3 small accessory spines. Dorsal surface covered
with short conical spines and acute tubercles of similar size.
Branchial regions neither markedly swollen nor contiguousin the carapace midline; cardiac region at least half as wideas long.

MAJIDAE Samouelle, 1819
Pleistacantha ori, new species(Figs. 1–5)
Pleistacantha moseleyi. – Stebbing, 1923: 2; Barnard, 1950: 34–35, Fig. 6e; Grindley, 1961: 127–128, Fig. 1a–d; Gordon, 1963:153; Berry & Hartnoll, 1970: 214–215, Pl. 1; Griffin, 1974: 27;
Kensley, 1981: 40; Zarenkov, 1994: 120, Fig. 13: 3, 4 [not P.
moseleyi (Miers, 1886)].
?Pleistacantha pungens. – Guinot & Richer de Forges, 1982: 1110–1112, Figs. 6A, B, 8A, A1, A2, Pl. 3: 2, 2a [not P. pungens(Wood Mason & Alcock, 1891)].

Epistome with ventrally directed spine lateral to antennal
gland aperture, and cluster of 5 or 6 spines midway between
antennal aperture and anterolateral angle of buccal cavity;
anterolateral angle of buccal cavity with 4 or 5 teeth.

Material examined. – Holotype: ZRC 2006.0158, male (cl 146.0mm, pcl 129.1 mm, cw 106.3 mm), off Durban, South Africa,trawled, coll. Oceanographic Research Institute, Durban, Oct. 2004.
Paratypes: ZRC 2006.0159, 1 male (cl 129.0 mm, pcl 115.0 mm,cw 92.7 mm), 1 ovigerous female (cl 120 mm, pcl 106.6 mm, cw83.9 mm), 1 spent female (cl 119.6 mm, pcl 104.9 mm, cw 84.5mm), same data as holotype.

Eye, when folded back into ‘orbit’, not extending past levelof antennal gland aperture. Eyestalk with elongate, stiff setaeon anterior margin.
Interantennular spine bifurcated in distal half to third, but
not divergent, depth of bifurcation decreasing with increasing
body size; distal margin of antennular sinus produced to stout,triangular, ventrolaterally directed spine. Basal antennularsegment with 2 or 3 ventrally directed spines; basal antennal
peduncle segment ventrally and distally spinose; penultimate
segment distally and ventrally spinose; ultimate segment withunarmed; flagellum extending slightly beyond rostral apices.

Others: MNHN B7272, 1 male (pcl 52.0 mm, cw 43.0 mm),Madagascar, 12°43'S 48°15'E, 360 m, trawl 10, A. Crosnier coll.,
14 Apr.1971; MNHN B7273, 1 male (cl 76.2 mm, pcl 62.0 mm, cw47.0 mm), Madagascar, 12°39.8'S 48°15.2'E, 375–385 m, trawl 11,A. Crosnier coll., 14 Apr.1971; MNHN B7274, 1 male (cl 83.0 mm,pcl 68.0 mm, cw 57.0 mm), Madagascar, 12°40.0'S 48°14.0'E, 410m, trawl 121, A. Crosnier coll., 11 Oct.1974.

Third maxilliped merus as wide as ischium; meral surface
spinose, with slender spine on either side of carpal
articulation, anterolateral margin triangular with spinose
margins; ischium with dentate margins, surface with conic
tubercles; without longitudinal groove.

Comparative material. – Pleistacantha pungens (WoodMason & Alcock, 1891): AM G1475, 1 male (cl 68.9 mm,pcl 55.8 mm, cw 44.7 mm), Andaman Sea, 238–458 m,RIMSS Investigator (ex Indian Museum 3180/9 as
Echinoplax pungens).

Third sternite of male spinous-tuberculate anteriorly, spinous
distally; remaining sternites spinose laterally. Third sterniteof female sparsely granulate. Male abdomen with 7 somites;
widest at somites 2 and 3; distinctly spinose; telson and sixth
somite clearly demarcated, but scarcely movable. Female
abdomen spinose, granulate. First pleopod of male (G1) gently
curving outwards, with distal tenth abruptly curved; subdistal
papilla on inner margin subequal in length to margin between
papilla base and pleopod apex, papilla straight, directed
obliquely; obtuse shoulder proximal to subdistal papilla.
Female abdomen with 7 somites, surface spinulous; telsonand sixth somite fused, forming ‘operculum’, demarcation
clearly visible; widest at somite 6.

Diagnosis. – Carapace with rostral spines 0.1–0.2 postrostral
carapace length; widely separated basally, subparallel orfaintly divergent; orbital margin with 5 or 6 well-spaced
spines increasing in size posteriorly; hepatic spine anteriorly
directed; dorsal surface covered with short conical spines andacute tubercles of similar size; branchial regions widely
separated, not contiguous in the carapace midline; cardiac
region at least half as wide as long. Anterolateral angle ofbuccal cavity with 4 or 5 teeth. Interantennular spine
bifurcated in distal half to third, but not divergent. Third
maxilliped merus as wide as ischium; anterolateral margin
triangular, spinose. Male abdomen with telson and sixthsomite clearly demarcated, but scarcely movable. First
pleopod of male (G1) with distal tenth abruptly curved; withobliquely directed subdistal papilla and obtuse shoulder
proximal to subdistal papilla. P5 merus 0.7 times postrostral
carapace length in males, 0.6 in females.

Male and female chelipeds dissimilar in adults. Male chela
distinctly inflated, granulate, non-spinous; carpus and merus
with row of stout conical spines along lower margins andinner surfaces, other surfaces covered with low, well-spaced
tubercles; occlusal margins of dactylus and pollex with blunt,obtuse teeth, with distinct gape; cheliped length 2.4–2.6 times
postrostral carapace length; dactylus 0.6 times palm length.
Female chela slender, markedly spinous; palm, carpus andmerus with longitudinal rows of slender, upright spines,
longest on lower and inner margins; occlusal margins ofdactylus and pollex dentate, with slight gape; cheliped length

Description of type material. – Carapace pyriform, postrostral
carapace length longer than width, length 1.2 times width inmales, 1.2–1.3 times width in females. Rostral spines 0.1–0.2 postrostral carapace length; widely separated basally,subparallel or faintly divergent; with 1 or 2 dorsal and 2
ventral (excluding basal) spines; with 3 lateral spines,

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Fig. 1. Pleistacantha ori, new species, male holotype (cl 146.0 mm, pcl 129.1 mm, cw 106.3 mm), ZRC 2006.0158: A, dorsal habitus; B,carapace, dorsal view; C, carapace, right lateral view; D, anterior carapace, right lateral view; E, right cheliped.

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Ahyong & Ng: New Pleistacantha from South Africa

Fig. 2. Pleistacantha ori, new species, male holotype (cl 146.0 mm, pcl 129.1 mm, cw 106.3 mm), ZRC 2006.0158: A, oral field; B, anterior
carapace, dorsal view; C, ventral surface; D, interantennular spine, anterior view; E, dactylus of right P2.

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Fig. 3 Pleistacantha ori, new species, female paratype (cl 119.6 mm, pcl 104.9 mm, cw 84.5 mm), ZRC 2006.0159. A, dorsal habitus; B,ventral view; C, left third maxilliped; D, right cheliped; E, interantennular spine, anterior view.

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Ahyong & Ng: New Pleistacantha from South Africa
1.2–1.3 times postrostral carapace length; dactylus 0.7 times
propodus length.

and corneous tips, those of P2 and P3 also with row of shortspines on lower margin and long curved spines on lateral
margins; dactyli of P2 and P3 about 0.5–0.6 times propodus
length, those of P4 and P5 about 0.6 times propodus length;
P5 merus 0.6 times postrostral carapace length.

Walking legs (P2–5) long, slender, decreasing in length
posteriorly. P2 about 3.3–3.4 times postrostral carapace length
in males, 2.6–2.8 in females.

Etymology. – The specific epithet is derived from the initialsof the Oceanographic Research Institute (ORI), Durban, andis used as a noun in apposition.

Male P2–4 propodus, carpus and merus granular, with short,widely spaced, upright spines; dactyli with dense soft setae
and corneous tip, those of P2 and P3 about 0.5 times propodus
length, those of P4 and P5 about 0.6 times propodus length;
P5 merus 0.7 times postrostral carapace length.

Remarks. – Pleistacantha ori, new species, is the largest
known species of the genus, and most closely resembles P.
moseleyi and P. pungens, with which it has been misidentified
by previous workers. Pleistacantha ori, new species, P.
moseleyi and P. pungens are readily distinguished fromcongeners by the relatively uniform dorsal carapace spination,in which the dorsal spines are of similar length rather thanhaving several gastric and branchial spines markedly longer
than the remainder, in combination with divergent rather than
medially appressed rostral spines, and a deeply bifurcateinterantennular spine.

Female P2–4 segments granular, strongly spinous, withlongitudinal rows of long, widely spaced, upright spines;
along lower and lateral margins; dactyli with dense soft setae

Pleistacantha ori, new species, more closely resembles P.
pungens than P. moseleyi in sharing less divergent,
proportionally shorter rostral spines (less than one-quarterversus about one-third to half postrostral carapace length).
Pleistacantha ori, however, is readily distinguished from bothP. pungens and P. moseleyi by the more widely separated
branchial regions of the carapace. In P. ori, new species, thebranchial regions are widely separated by the cardiac region,
which is at least half as wide as long (Figs. 1A, B; 3A). In

Fig. 4. Pleistacantha ori, new species, male holotype (cl 146.0 mm,pcl 129.1 mm, cw 106.3 mm), right male pleopod 1 (G1), ZRC
2006.0158: A, abdominal view; B, apex, sternal view. Scale bar =2.0 mm.

Fig. 5. Colours in Life. Pleistacantha ori, new species: A, maleparatype (cl 129.0 mm, pcl 115.0 mm, cw 92.7 mm), ZRC
2006.0159; B, female paratype (cl 120 mm, pcl 106.6 mm, cw 83.9mm), ZRC 2006.0159.

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P. pungens and P. moseleyi, however, the branchial regions
are nearly approximated in the longitudinal midline so thatthe cardiac region resembles a narrow ‘hour-glass’ in shape(Fig. 6).

The specimens from Madagascar agree well in most respects
with the South African material, including gonopod
morphology, but differ in the more pronounced generalspination of the carapace and pereopods and proportionallylonger rostra (0.22–0.23 versus 0.12–0.15). Each of theaforementioned features vary allometrically and are consistent
with the considerable size difference between the South
African and Malagasy specimens, the latter being about half
the size of the former. As such, we regard them as conspecificwith the types of P. ori, new species, from Durban.

The sexual dimorphism observed in P. ori is consistent withthat reported by Grindley (1961) for the species (as P.
moseleyi): the walking legs are less spiny and the chelipeds
more inflated and more elongate in adult males. The specimen
from Natal reported by Stebbing (1923) and Gordon (1963)
was ovigerous at 102.5 mm pcl, but females apparently mature
at a smaller size. Berry & Hartnoll (1970) reported on matingin captivity of P. ori, new species (as P. moseleyi) between
a male of 108 mm pcl and an already berried female of 81mm pcl. Stebbing (1923) and Berry & Hartnoll (1970)
described the eggs as violet or purple in colour, respectively.

The specimen reported by Griffin (1974) from off Durban asP. moseleyi is almost certainly referable to P. ori, new species.
Several authors have speculated on the identity of juvenile
East African specimens of a Pleistacantha reported by Doflein(1904: Pl. 24, Figs. 5, 6) as P. moseleyi. Doflein’s (1904)
specimens should be re-examined, but the well-separated
branchial regions exclude the possibility that they are P.
moseleyi or P. pungens; they perhaps represent juvenile P.
ori, new species, or an undescribed species. Other specimens
reported by Doflein (1904) from Grand Nicobar Island(Andaman Sea) and Sumatra (Indonesia) are referable to P.
pungens and P. griffini Ahyong & Lee, 2006, respectively.

Griffin & Tranter (1986a) reported allometric variation in P.
oryx in which the interantennular spine was divided in thedistal third in juveniles ranging to less than one-third in adults.
In P. ori, new species, the interantennular spine is bifurcate
for the distal third to half, being shallowest in the largest
specimen. Provided that the range of allometric variation isconsidered, the depth of the bifurcation in the interantennularspine remains a reliable diagnostic character in Pleistacantha.

Distribution. – Presently known only from off the Natal coast,
South Africa and Madagascar; 238–480 m.

ACKNOWLEDGEMENTS
We are grateful to Sean Fennessy (ORI) for referring theinteresting material to us for study and for his colour
photographs. Danièle Guinot, Alain Crosnier and Regis Cleva(MNHN) kindly assisted with access to the material in theMuséum national d’Histoire Naturelle, Paris. The study was
made possible by Biosecurity New Zealand (contract ZBS
2005-24) and Visiting Fellowships to the first author fromthe Raffles Museum of Biodiversity Research and Muséum
national d’Histoire naturelle, Paris.

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