THE RAFFLES BULLETIN OF ZOOLOGY 1999 Supplement No. 6: 189-196
0 National University of Singapore

A NEW SPECIES OF GEOSESARMA(CRUSTACEA: DECAPODA: BRACHYURA: GRAPSIDAE)
FROM PULAU TIOMAN, PENINSULAR MALAYSIA
Darren C. J. Yeo and Peter K. L. Ng
Department of Biological Scienct~s.Ftrcrc1f.v of St.ient.e, the Nutionul Univer.sity of Singcrpore,
10 Kent Ridge Creswnt. Singapore 119260, Republic of Singapore-ABSTRACT. A new species of terrestrial grapsid crab of the genus Geosesarmn isdescribed from Pulau Tioman. Peninsular Malaysia. Geosesarmu nlbomita, newspecies, is endemic to the island, and distinguishable from its congeners by a
combination of G I , ambulatory leg and carapace characters.

KEY WORDS. - Geo.\esurrm, Grapsidae. Pulau Tioman, new species

INTRODUCTION
Faunistic surveys were conducted by staff and students of the Department of BiologicalSciences. the National University of Singapore, on Pulau Tioman, Peninsular Malaysia. during
three recent expeditions (1995-1997). Collections were also made from the tallest mountainon the island, Gunung Kajang. Specimens of a new species of terrestrial grapsid crab
belonging to the genus Geosesarma were obtained through these collections, bringing thetotal number of freshwater or terrestrial crab species reported from Pulau Tioman to 12 (seeYeo et al., 1999).
Geosesarma albomita, new species, most closely resembles Geosesarma tiomanicum Ng,
1986, but may also be confused with G. serenei Ng, 1986, and G. scandens Ng, 1986. It is,however, distinguished from these congeners by various aspects of the G1, ambulatory leg
form and carapace shape.

The following abbreviations are used: G1 for male first pleopod, G2 for male second pleopod.
Measurements are of carapace width and length respectively. Terminology used essentiallyfollows Ng (1988). All measurements are in millimetres. Specimens examined are depositedin the Zoological Reference Collection (ZRC) of the Raffles Museum, National Universityof Singapore. Malay words used in the text are 'Pulau' (island), 'Sungai' (river or stream),'Gunung' (mountain) and 'Kampung' (village).
Received 24 Oct 1996

Accepted 19 Aug 1997189

Yeo & Ng: New species of Geosesarnia

TAXONOMYFAMILY GRAPSIDAE MACLEAY. 1838

Geosesarma albomita, new species(Figs. 1-2)
Geosesmrma tiomanicu~n- Ng & Lim, 1989: 3 1 (part)(not Geosesarma tiommica, Ng, 1986).

Material examined. - Holotype - male (9.5 by 8.8 mm)(ZRC 1996.1717). Gunung Kajang. Pulau
Tioman. Pahang, Peninsular Malaysia, 3000 ft ad., among leaf litter, coll. T. H. T. Tan et al., 27Jun. 1996. Paratypes - 2 males 1 female (largest 9.2 by 8.4 mm)(ZRC 1996.1718), same data as
holotype. Others - 1 male (7.4 by 6.6 mm) (ZRC 1990.9165), Malaysia. Pulau Tioman, GunungKajang, 3360 ft. coll. J. A. Bullock, 19 Apr.1962.

Description of holotype. - Carapace squarish, slightly broader than long, dorsal surfaces
covered with small granules; regions distinctly demarcated, with relatively deep grooves;median gastric groove deep. H-shaped; anterior grooves shallow; transverse groove separating
cardiac and intestinal region distinct (Fig. 1A). Frontal margin strongly deflexed, gently
sinuous, appearing weakly bilobed, subcristate, postfrontal cristae distinct, sharp, separated
by deep median groove, each crista bilobed, each lobe separated by shallow groove, surfaceof frontal region vertically concave (Fig. IA). External orbital angle acutely triangular,
directed obliquely outwards, separated from first epibranchial tooth by distinct, deep, Vshaped cleft; first epibranchial tooth smaller than external orbital angle, triangular, with very
shallow notch posterior to it, demarcating it from the lateral margin, second epibranchial
tooth indistinct (Fig. IA). Lateral margins straight to gently diverging posteriorly;
posterolateral regions with low oblique striae. Eyes large, reaching or extending beyond tipof external orbital angle (Fig. 1A).
Merus of third maxilliped with mid-portion of lateral margin slightly produced as blunt angle,
widest point about two times greater than proximal margin width, with strong median oblique
ridge; ischium with shallow median sulcus and distinct outer ridge; exopod slender, notreaching midlength of merus, lacking flagellum, with numerous long setae distally (Fig.
1 Dl.
Chelipeds subequal: outer surface of palm granulose, covered with low, scattered granules,
especially on upper and lower margins; fingers subequal to length of palm, proximal part ofupper margin of left chela dactylus lined with 12 low, forward-directed granules (ten granules
on right chela dactylus), cutting edge lined with numerous teeth and denticles, distal part offinger pectinated to form blade-like cutting edges; carpus inner margin gently serrated, innerdistal spine weak but distinct, with scattered low granules on dorsal surface; outer surfaceof merus slightly rugose. inner surface smooth, with serrated inner margin, without subdistal
spine (Fig. lC, E).
Second pair of ambulatory legs longest; merus broad, with low, truncated subdistal dorsal
tooth, upper margin very gently serrated; dactylus shorter than propodus, straight, gently
curved distally; segments lined with numerous short. stiff spiniform hairs (Fig. 2E, F).
Abdomen triangular, lined with numerous short setae; seventh segment with rounded tip.
longer than sixth, lateral margins of sixth and seventh segments convex (Fig. 1B).

THE RAFFLES BULLETIN OF ZOOLOGY 1999 Supplement No. 6

Fig. 1. Geosesarrna albomita, new species. A-E, Holotype male (9.5 by 8.8 mm)(ZRC 1996.1717),
Gunung Kajang, Pulau Tioman, Peninsular Malaysia; F, Paratype female (9.2 by 8.4 mm)(ZRC1996.1718), same locality. A: carapace; B: abdominal segments 5-7; C, F: left chela; D: left thirdmaxilliped; E: carpus of left cheliped. B with marginal setae not drawn in. Scales = 5.0 mm in A; 2.0mm in B-F.

Yeo & Ng: New species of Geosesarma

Fig. 2. Geosescrrmo albomira, new species. Holotype male (9.5 by 8.8 mm)(ZRC 1996.17U ) , Gunung
Kajang, Pulau Tioman, Peninsular Malaysia. A: dorsal view of left G I ; B: median view of left G I ;C: ventral view of left G I ; D: left G2; E: left second ambulatory leg; F: left fourth ambulatory leg.
A-C, E-F with s e m not drawn in. Scales = 1.0 mm in A-D; 2.0 mm in E-F.

THE RAFFLES BULLETIN OF ZOOLOGY 1999 Supplement No. 6
G 1 relatively slender; distal part directed obliquely outwards, pectinated. elongated, straight,
gently tapering, upper margin slightly convex, tube-like, with distal opening on dorsal side,
laterally flattened towards ventral side; proximal part with deep distal cleft on outer margin,
inner margin slightly produced as a weak, barely distinct hump distally, inner surface flattened
to slightly concave distally, subdistal non-pectinated portion with numerous setae obstructing
view of distal part of G 1 (Fig. 2A-C). G2 very short, lacking flagellum. expanded proximally,
tapered distally, curved, with distal part directed outwards (Fig. 2D).

Paratypes. - The paratype males are slightly smaller than the holotype but agree in all othermajor aspects. The paratype female agrees with the males in most non-sexual characters
except that the fingers of the female chelae appear more slender and relatively longer thanthose of the males, with the distal pectinated cutting edges extending further posteriorly toapproximately one third of the finger length (Fig. IF).
Etymology. - From Latin words albus meaning white and mittr meaning mitten, alluding to
the unique white colouration of the chelae. Used as a noun in apposition.
Colour. - In live specimens, the dorsal carapace i:, dark brown gradually becoming tinged
with light purpl~sh-greyfrom anterior to posterior. The eyes are bright yellowish. The carpiof the chelipeds are light purplish dorsally and dark brown on the outer face, while thechelae are white. 'The ambulatory legs are generally brownish in colour except for the innerface of the meri being light purplish-grey.

-Remarks. Geosesarmn albomita, new species, belongs to the Gcosesarma malayanurn groupof species. in that it is a highland species; the third rnaxilliped exopod lacks a flagellum; theGI distal part is short, bent and tapered; and the ambulatory meri are broad (sensu Ng.
1988). Other species from Peninsular Malaysia belonging to this group which closely
resemble G. albotnita, especially in terms of superficial similarity of the G1, include
Geosesartna tiomanicum Ng, 1986, G. serenei Ng: 1986. and G. scrrnderis Ng, 1986.
Geosescwma albomircr can easily be distinguished from G. serenei (known only from Perak,Malaysia) by the presence of one epibranchial tooth (versus two): the broad ambulatory leg
merus (versus narrow); the distal part of the GI being more stout, having no distinct humpon the inner margin and being more obliquely bent (versus GI distal part being more slender.
having a gentle but distinct hump on the inner margin and being less obliquely bent).
Geosesarma alboinita differs from G. scntztkens (known only from Selangor, Malaysia) in
having a less sinuous frontal margin (versus more sinuous) and a slightly more slender GI
with a weak hump on the inner margin of the proximal purt distal portion (versus a stouter
GI with strong, distinct hump on the inner margin of the proximal purt distal portion).
However, G. ~zlbomitclis most likely to be mistaken for G. tiomanicuni (see Fig. 3), as they
are very closely related, with almost identical external characters, and both are found on
Pulau Tiornan (but as far as is known, on adjacent mountains). The former species can beseparated from the latter species primarily by the following differences: i) G 1 more slender;i i ) distal part of G 1 proportionately longer: iii) inner margin of proximal part of GI produced
as a hardly distinct, weak hump distally (versus gentle but distinct hump); iv) rectangularcleft on outer margin of G 1 subterminal part with more angular corners (versus more roundedcorners): v) merus of ambulatory leg with low, truncated subdistal dorsal tooth (versus welldeveloped, acute subdistal tooth): and vi) carapace more squarish with width subequal tolength (versus more rectangular with width greater than length)(see Figs. 1-3). A reexamination of the G 1 of the small male specimen (ZRC 1990.9165) from Gunung Kajang,Yeo & Ng: New species of Geosesatmn

Fig. 3. Geoscsarma rionranicum Ng, 1986. Holotype male (10.7 by 10.2 mm)( ZRC 1965.7.29.13),"Tanah Runtuh", north of Gunung Rokam, Pulau Tiornan, Peninsular Malaysia. A: carapace; B: leftsecond ambulatory leg; C: left fourth ambulatory leg; D: dorsal view of left GI; E: ventral view of
distal portion of left GI. 9-Ewith setae not drawn in. Scales = 5.0 mm in A; 2.0 mrn in B-C. (D, E,after Ng, 1986).

THE RAFFLES BULLETIN O F ZOOLOGY 1999 Supplement No. 6
identified as G. tiomanicutn by Ng & Lim (1989), has shown that it clearly belongs to G.
albomita instead.
The GI of Geosesarma albomita, new species, also bears close resemblance to Geosesarma
insulare Ng, 1986, and G. katibas Ng, 1995, from Anambas Islands and Borneo respectively.
However, the G l s of G. insulare and G. katibas are more stout than that of G. alhomita. In
addition, Geosesarma albotnita is also differentiated from these two species by the low.
truncated subdistal dorsal tooth on the ambulatory leg merus (versus well developed, acutesubdistal tooth). Furthermore, in the G1 of G. ulbomita, the subdistal outer margin cleft isdistinctly rectangular (versus rounded in G. katibas), the distal part is more obliquely bent(versus more horizontally bent in G. insulare). The first epibranchial tooth of G. nlbomita
also differs from that of G. katibas in that it is strong and triangular in shape (versus weak,rounded).
Geosesarma alhomita, like other members of this terrestrial genus, probably bears relatively
large eggs from which fully developed juvenile crabs hatch out (see Ng & Tan, 1995). Thisdispenses with the need to return to water to release larvae, making this group truly well
adapted to life on land.

Distribution. - Gunung Kajang, Pulau Tioman, Pahang, Peninsular Malaysia.
Comparative material. - Geosesarma tiommicum Ng. 1986 - Holotype male (10.7 by 10.2mm)(ZRC 1965.7.29.13), "Tanah Runtuh", north of Gunung Rokam, ca. 2'52'39"N
104'1 1'48"E, coll. N. Smedley, May.1929. Paratype male (ZRC 1965.7.29.14), same data
as holotype.

ACKNOWLEDGMENTS
We are grateful to the staff and students involved in the recent expeditions to Pulau Tioman
for helping in the collection of specimens; and C. M. Yang (ZRC) and Kelvin Lim for accessto material under their care. This study was partially supported by research grant RP950360
to the second author by the National University of Singapore.

LITERATURE CITED
MacLeay, W. S.. 1838. Illustrations of the Annulosa of South Africa; being a portion of the objectsof natural history chiefly collected during an expedition into the interior of South Africa, under
the direction of Dr. Andrew Smith, in the years 1834, 1835 and 1836; fitted out by the "Cape ofGood Hope Association for Exploring Central Africa". In: A. Smith, Illu.rirutions ($the Zoolog?;of South Africa Investigations, London, Sith, Elder and Co., pp. 1-75, Pls. 1-4.
Ng, P. K. L.. 1986. Preliminary Descriptions of 17 New Freshwater Crabs of the Genera Geosesarrnu,Purathelphuscr, Jolwru and Stolic,-in (Crustacea, Decapoda, Brachyura) from South East Asia. J.
Singapore Nutn. Acud. Sci., 15: 36-44.
Ng, P. K. L., 1988. The Freshwater Crabs oj'Peninsular Malaysin und Singapore. Dept. Zool., Natn.
Univ. Singapore, Shinglee Press, Singapore, pp. i-viii, 1-156, 4 colour plates.

Ng: P. K. L., 1995. On one new genus and three new species of freshwater crabs (Crustacea: Decapoda:Brachyura: Potamidae and Grapsidae) from Lanjak-Entimau. Sarawak, East Malaysia, Borneo.
Zool. Med., Leiden, 69(5): 57-72.

Yeo & Ng:New species of Geosesarrnc~Ng. P. K. L & R. P. Lim. 1989. Contributions to the Freshwater Crab Fauna of Pulau Tioman.
Peninsular Malaysia (Crustacea: Decapoda: Brachyura). J. Sitzgapore Natn. Acad. Sci., 17: 28-32.
Ng, P. K. L. &i C. G. S. Tan, 1995. Geosesarma t~orophorumsp. nov. (Decapoda. Brachyura, Grapsidae,Sesarminar), a Terrestrial Crab from Sumatra, with Novel Brooding Behaviour. Cru.staceana,Leiden, 68(3): 390-39.5.
Yeo. D. C. J.. Y. Cai & P. K. L. Ng, 1999. The freshwater and terrestrial decapod crustacea of Pulau
Tiornan, Peninaular Malaysia. Rafles Bull. Zool., Suppl. 6. 197-244.