A New Cavernicolous Species Of Freshwater Crab (Crustacea : Brachyura : Potamidae) From Pulau Tioman, Peninsular Malaysia

6 Pages·2001·2.4 MB·

by  Darren C J Yeo

PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTON
114(3):618-623. 2001.
A new cavernicolous species of freshwater crab (Crustacea:
Brachyura: Potamidae) from Pulau Tioman, peninsular Malaysia
Darren C. J. Yeo
Raffles Museum of Biodiversity Research, Department of Biological Sciences,
National University of Singapore, 10 Kent Ridge Crescent, Singapore 119260.
—
Abstract. A new freshwater potamid crab species, Johora gua, is described
from Pulau Tioman, an island offthe east coast ofPeninsular Malaysia. Itdiffers
from most of its congeners by the relatively longer and slenderer ambulatory
legs as well as various other characters in the carapace and male first pleopod.
This is the fifth species of Johora Bott to be described from Pulau Tioman,
and the first cavernicolous crab to be reported from Peninsular Malaysia.
Specimens of an unusual freshwater crab has yet to be discovered. The new species
recently collected from a cave on Pulau of Johora herein described is the first true
Tioman, an island offthe east coast ofPen- cavernicolous freshwater crab to be report-
insular Malaysia, proved to be a new po- ed from Peninsular Malaysia. The cave-
tamid species of the genus Johora Bott, dwelling habits of this species are, to some
1966. This new species differs from most extent, reflected in slight troglomorphic fea-
ofits congeners by the relatively longerand tures although these are less significant
slenderer ambulatory legs as well as various when compared with other known caver-
other characters of the carapace and male nicolous crabs.
first pleopod. The genus Johora Bott, 1966 The following abbreviations are used:
[type species: Potatnon (Potamon) johor- Gl, male first pleopod; G2, male second
ense Roux, 1936], is endemic to the Malay pleopod; cw, carapace width; and asl, above
Peninsula, occurring northwards from Sin- sea level. Measurements are given in mil-
gapore into the southern half of Peninsular limeters (mm) as carapace width X length.
Malaysia along the central highlands. Spe- Terminology used essentially follows Ng
cies of this genus are replaced by those of (1988). Malay words used in the text are
Stoliczia Bott, 1966, in the northern half 'Pulau', island; 'Qua', cave; and 'Gunung',
through to southern Thailand (Ng 1988). A mountain. Specimens remain deposited in
total of 13 species have been placed in Jo- the Zoological Reference Collection, Raf-
hora, with Pulau Tioman alone accounting fles Museum of Biodiversity Research, De-
for four species, all island endemics, viz., partment of Biological Sciences, National
J. counsilmani (Ng, 1985), /. grallator Ng, University of Singapore (ZRC). As com-
1988, J. punicea (Ng, 1985), and /. tiom- parative material, the types and supplemen-
anensis (Ng & Tan, 1984) (see Ng 1988, tary specimens of the other four Johora
1990; Ng & Takeda 1992; Yeo et al. 1999). species from Pulau Tioman in the ZRC
In the present study, the fifthJohora species were examined. A detailed listing of this
known from Pulau Tioman is described, material can be found in Yeo et al. (1999).
bringing the total number in the genus to
Johora gua, new species
14.
Ng (1988: 142) earUer referred to the Figs. lA-C, E-—H, 2A-G
". .existence of an unknown species of Material examined. Holotype: male
.
white crab in Malayan caves. ." but this 11.4 X 8.5 mm (ZRC 2000.2236), Gua
.
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114, 3 619
Tengkuk Ayer, route to Gunung Kajang hora gua, new species, were obtained sev-
m
from Juara, Pulau Tioman, ca. 900 asl.. eral meters inside a small granite cave, not
& m
Peninsular Malaysia, coll. H. H. Tan T. higher than 1 in height, with a shallow
M. Leong, 1 Sep 2000. Paratype: male 9.5 underground stream, about 2-15 cm deep,
X 7.2 mm (ZRC 2000.2237), same data as flowing slowly over sandy and rocky sub-
holotype. — stratum. The water pH was 7.8. No surface
Diagnosis. Carapace distinctly broader (epigeal) streams were found in the vicinity
than long, not elevated; dorsal surface flat, (T M. Leong & H. H. Tan, pers. comm.;
glabrous. Epigastric cristae distinctly ru- Ng et al. 1999: 171). Organic input into this
gose; postorbital cristae not sharp, rugose. system include swiftlet and porcupine drop-
Frontal region smooth; antennular fossae pings. Tadpoles of a species ofmegophyrid
broadly subrectangular; corneas slightly re- frog, Leptolalax gracilis (Giinther), and a
duced, about 0.4 times length of eyestalks. species of fish, the blind cave loach, Sun-
External orbital angle low, broadly trian- doreonectes tiomanensis Kottelat, were
gular, outer or lateral margin about 4 times found syntopically, along with the fully
longer than inner or medial margin; epi- aquatic freshwater crab species J. tioma-
branchial tooth weak, triangular; anterolat- nensis (T M. Leong & H. H. Tan, pers.
eral margin gently convex, very weakly comm.). Despite its presence in the cave,
cristate; branchial region indistinctly ru- and the absence of surface streams nearby,
gose; metabranchial region with distinct /. tiomanensis is still regarded as an epigeal
oblique striae. Epistome with weak, broadly species, as it is commonly found in surface
triangular median tooth on posterior mar- streams at lower altitudes throughout the
gin. Third maxilliped exopod with well-de- southern half of the island (see Yeo et al.
veloped flagellum, longerthan merus width. 1999). —
Cheliped with carpus armed with robust Remarks. Johora gua, new species, is
subdistal spine on inner margin. Ambula- immediately separated from all its conge-
tory legs sparsely setose, long, slender; dac- ners except J. grallator Ng, 1988, by its
tyli elongated, slender, merus unarmed. Su- much longer and slenderer ambulatory legs.
ture between anterior thoracic sternites 2 Johora gua could be mistaken for ajuvenile
and 3 faint; thoracic sternite 8 completely of/. grallator, as they are superficially sim-
separated by longitudinal median line, lack- ilar in the long, slender legs as well as light
ing transverse ridge on midline; abdominal orange live coloration (see Yeo et al. 1999).
cavity reaching imaginary line joining an- However, specimens of /. gua are much
terior edge of cheliped bases. Male abdo- smaller, similar in size to the holotype (11.4
men triangular. Gl terminal segment about X 8.5 mm, ZRC 2000.2236), which clearly
0.4 times length of subterminal segment, possesses well-developed adult Gls. In
very slender, subcylindrical, curved out- contrast, two similar sized male specimens
wards, lacking dorsal flap; subterminal seg- of7. grallator (largest 11.7 X 8.9 mm, ZRC
ment distinctly broader in proximal half, 1996.1730) have undeveloped Gls and are
not neck-like distally, without shelf or cleft clearly juvenile. The ambulatory legs of J.
on upper part of outer margin. G2 distal gua dire, relatively stouter than those of J.
segment distinctly longer than half ofbasal grallator, as reflected in the proportions of
segment. the merus of the second leg (4.3-4.4 vs.
—
Color. Live specimens are light orange 5.3-5.7 times longer than broad); and mer-
in overall colo—ration. us of the fourth leg (3.4-3.6 vs. 4.4-4.7
Etymology. The specific name, "gua", times longer than broad) (Fig. 2A, B; Ng
is Malay for cave, alluding to its cavernic- 1988: fig. 23A). Furthermore, J. gua differs
olous habitat. Used—as a noun in apposition. from /. grallator in the following charac-
Ecological notes. The specimens ofJo- ters: postorbital cristae relatively more ru-
620 PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTON
gose and less sharp (vs. postorbital cristae segment that lacks a dorsal flap, and a rel-
distinctly smoother and sharper); corneas atively broad subterminal segment that
reduced, shorter than half the length of the lacks a distinct distal cleft on the outer mar-
eyestalks (vs. normal-sized corneas, about gin (see Fig. 2C-F, H; Yeo et al. 1999: fig.
half the length of the eyestalks); antennular 6B-D). However, J. gua can be distin-
fossae distinctly broader than the epistome guished from /. punicea by the distinctly
(vs. antennular fossae as broad as epi- slenderer ambulatory legs (e.g., dactylus of
stome); and epistome posterior margin with second leg 11.4-15.0 vs. 5.9-7.5 times lon-
poorly developed median tooth (vs. epi- ger than broad; second ambulatory leg mer-
stome posterior margin with well-devel- us 4.3-4.4 vs. 3.5-4.0 times longer than
oped median tooth) (Fig. lA, C; Ng 1988: broad) (Fig. 2A, B; Ng & Chong 1986; Ng
fig. 23A, B; Yeo et al. 1999: fig. 5A, B). 1988: pi. 1 fig. D, fig. 22A); Gl terminal
The shape of the Gl of 7. grallator is un- segment being less strongly hooked or out-
known, as no mature males have been col- wardly curved (vs. Gl terminal segment
lected (see Ng 1988; Yeo et al. 1999). How- more strongly hooked or curved outwards
ever, the external morphological differences in appearance); and Gl subterminal seg-
discussed are sufficient to show thatthe two ment being relatively slenderer (vs. Gl sub-
species are clearly not conspecific. Most of terminal segment relatively broader) (Fig.
these external differences are also applica- 2C-F, H; Yeo et al. 1999: fig. 6B-D). Fur-
ble in distinguishing J. gua from /. tioma- thermore, specimens ofJ. punicea are larg-
&
nensis (Ng Tan, 1984), and /. counsil- er than those of J. gua, with specimens of
mani (Ng, 1985), two other large, fully J. punicea (e.g., male, 11.3 X 8.8 mm, ZRC
aquatic Johora species that are endemic to 1996.1733) similar in size to the holotype
Pulau Tioman (see Ng 1988: figs. 20A, B, of J. gua (11.4 X 8.5 mm, ZRC
21A, B). In addition, J. gua can be further 2000.2236), possessing undeveloped juve-
separated from these species by its almost nile Gls (Fig. 21, J).
smooth sub-branchial, sub-hepatic and pter- In addition to the above primary differ-
ygostomial regions (vs. sub-branchial, sub- ences, /. gua can also be immediately sep-
hepatic and pterygostomial regions distinct- arated from juvenile as well as adult spec-
ly rugose); and by its Gl terminal segment imens of/. punicea by its light orange live
always lacking a dorsal flap (vs. Gl ter- coloration (vs. deep purple in large adults;
minal segment with dorsal flap); and Gl pink to light purple in juveniles) and pro-
subterminal segment lacking a distal cleft portionately smaller corneas, about 0.4
on the outer margin (vs. Gl subterminal times length of the eyestalks (vs. normal-
segment with a distinct subrectangular dis- sized corneas, subequal to half length of
tal cleft on the outer margin) (Figs. IC, 2C- eyestalks) (Fig. lA, C, D; Ng & Chong
F; Ng 1988: figs. 20B, 21B; Yeo et al. 1986; Ng 1988: pi. 1 fig. D, fig. 22A, B).
1999: figs. 4A-C, F-H, 7B-E, G-H). These secondary characters, together with
Johora gua is most similar to J. punicea the long and slender ambulatory legs seem
(Ng, 1985), also from Pulau Tioman. Both to reflect the cave-dwelling habit of/. gua.
species share a relatively smooth carapace It is interesting to note here that /. gua is
dorsal surface, with weakly cristate antero- more similar to juvenile specimens of J.
lateral margins, and relatively blunt post- punicea, which have relatively slenderer al-
orbital cristae, and very low, poorly devel- beit undeveloped Gls, lighter pigmentation
oped epistome posterior margin median and slenderer ambulatory leg segments
tooth (Fig. lA, C; Ng 1988: fig. 22A, B). compared to adult specimens, suggesting a
The Gl structure in both species is also possible progenetic origin for J. gua from
very similar in having a long, slender out- J. punicea.
wardly curved or sickle-shaped terminal Johora gua appears to be a true caver-
VOLUME NUMBER
114, 3 621
Fig. 1. A-C, E-H, Johora gua, new species, holotype male (11.4 X 8.5 mm) (ZRC 2000.2236); D, Johora
punicea (Ng, 1985), male (11.3 X 8.8 mm) (ZRC 1996.1733). A, dorsal view ofcarapace; B, left third maxil-
liped; C, D, frontal view ofcarapace, left side; E, dorsal view ofcarpus ofright cheliped; F, anterior thoracic
sternum (sternites 1-4); G, male abdomen; H, posterior thoracic sternum (sternites 5-8). Scales = 2.0 mm (A,
mm
C, D, F-H); 1.0 (B, E).
622 PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTON
Fig. 2. A-G, Johora gua, new species, holotype male (1L4 X 8.5 mm) (ZRC 2000.2236); H-J, Johora
punicea (Ng, 1985), H, holotype male (19.7 X 15.5 mm) (ZRC 1984.6803) (afterNg, 1988), I, J, male (11.3 X
8.8 mm) (ZRC 1996.1733). A, right second ambulatory leg; B, right fourth ambulatory leg; C, I, dorsal view
ofright Gl; D, J, ventral view ofright Gl; E, dorsal view ofright Gl terminal segment; F, ventral view ofright
Gl terminal segment; G, right G2; H, ventral view ofleft Gl. Scales = 2.0 mm (A, B); 1.0 mm (G, I, J); 0.5
mm
(C-F).
——
VOLUME NUMBER
114, 3 623
nicolous species, as it has not been found Guinot, D. 1988. Lescrabescavernicolesdumonde.
in any surface streams on Pulau Tioman de- Memoires de Biospeologie 15:1-40.
Ng, R K. L. 1985. Freshwater decapod crustaceans
spite extensive and intensive sampling on —
from Pulau Tioman, West Malaysia. Zoolo-
the island over several years (see Yeo et al. gische Mededelingen 59:149-162.
1999). In addition, J. gua possesses a com- . 1988. The freshwatercrabs ofPeninsularMa-
bination of troglomorphic features in its laysia and Singapore. Department of Zoology,
proportionately long, slender ambulatory National University of Singapore, Shinglee
pleiggsm,enstliagthitolny (rreedluatcievde tcoorJn.epausniacnedaraeddulutcse)d. P(.rCer1su9ss9,t0a.ScienaAg:apnDoeerwcea,pspo1ed5ca6i:epspB..roafFciJhgyosuh.roa1r:-a63PB.oottta,mi1d9a6e6)
Such features are commonly seen in various fromPulau Redang, Trengganu, PeninsularMa-
—
combinations and degrees in troglobitic laysia. Journal of Natural History 24:305-
crabs in response to life in a cave habitat, 310.
where light is either severely reduced oren- . 1991. Cancrocaeca xenomorpha, new genus
and species, a blind troglobitic freshwater hy-
tirely absent, and the sense of touch be-
menosomatid (Crustacea: Decapoda: Brachyu-
cotom1e98s8;moNrge&impSokrettan1t99t6h;anYesiogh&t (Nsgee1G9u9i9n)-. roaf)ZforoolmogSyul3a9we:s5i9,-7I3n.donesia.—Raffles Bulletin
Johora gua, however, may be an incipient , & S. S. C. Chong. 1986. The—freshwatercrabs
troglobite as its troglomorphic features are and prawns of Pulau Tioman. Nature Malay-
not as highly specialized as that of other siana, Kuala Lumpur 11:26-31.
known troglobitic crabs, such as the potam- , & B. Sket. 1996. The freshwater crab fauna
id Erebusa calobates Yeo & Ng, 1999, i(pCpriunsetsa.ceIaV:.—ODencaapcoodlal:ectBiroancohfyuPraar)atohfeltphheusPihdiale-
from Laos, which has much longer and fromBohol. ProceedingsoftheBiologicalSo-
slenderer legs together with reduced eye- ciety ofWashington 109:695-706.
stalks and corneas; the parathelphusid Sun- , & M. Takeda. 1992. On some freshwater
dathelphusa sottoae Ng & Sket, 1986, from crabs (Crustacea: Brachyura: Potamidae, Par-
athelphusidae and Grapsidae) from Peninsular
Philippines, which has very reduced pig- —
Malaysia. Bulletin of the National Science
mentation as well as corneas; and the hy- Museum, Tokyo, Series A (Zoology) 18:103-
menosomatid Cancrocaeca xenomorpha 116.
W
Ng, 1991, from Sulawesi, which has very , &L. H. Tan. 1984. Anewfreshwatercrab.
long, slender legs, and no pigmentation, Stoliczia {Johora) tiomanensis n. sp. (Decapo-
eyes or orbits (see Ng 1991; Ng & Sket da: Brachyura: P—otamidae) from Pulau Tioman,
1996; Yeo & Ng 1999). W1e6s7t-17M4a.laysia. Malayan Nature Journal 37:
Ng,H. H., H. H.Tan, &K. K.PLim. 1999.Theinland
Acknowledgments
fishes ofPulau Tioman, PeninsularMalaysia.
I am grateful to P. K. L. Ng for his con- Raffles BulletinofZoology, supplement6:169-
structive criticism of the manuscript; T. M. 187.
Leong and H. H. Tan for collecting the Roux, Jc.ru1s9t3a6c.eaSnsecfornodmntohteeMuaploanyfPreensihnwsautlear.—deBcualploed-
specimens and providing the interesting tin of the Raffles Museum, Singapore 12:29-
ecological observations; and C. M. Yang 33, pis. 12-13.
and K. L. Yeo (ZRC) for access to material Yeo, D. C. J., & P K. L. Ng. 1999. Erebusacalobates,
under their care. new genus, new species, a trog—lobitic crab
(Brachyura: Potamidae) fromLaos. Journalof
Crustacean Biology 19:908-916.
Literature Cited , Y.-X. Cai, & P K. L. Ng. 1999. The fresh-
Bott,R. 1966.PotamidenausAsien{PotamonSavigny water and terrestrial Decapod Cru—stacea ofPu-
und—Potamiscus Alcock) (Crustacea, Decapo- lauTioman, PeninsularMalaysia. RafflesBul-
da). Senckenbergiana biologica 47:469-509. letin ofZoology, supplement 6:197-244.