Corresponding author: Peter K. L. Ng (
Academic editor: I. Wehrtmann
Seven species of freshwater crabs from three families are recorded from and around the Danum Valley Conservation Area in Sabah, Malaysian Borneo:
Ng PKL, Ng PYC (2018) The freshwater crabs of Danum Valley Conservation Area in Sabah, East Malaysia, with a description of a new species of Thelphusula Bott, 1969 (Crustacea, Brachyura, Gecarcinucidae, Potamidae, Sesarmidae). ZooKeys 760: 89–112.
Danum Valley Conservation Area, northeastern Borneo, in the Malaysian state of Sabah contains over 400 square kilometres of pristine rainforest and is a key conservation area on the island (
Here we review and add to the freshwater crab fauna of the Danum Valley Conservation Area. Specimens of a recently collected
The terminology used follows that in
Holotype: male (23.9 × 18.4 mm) (
Carapace broader than long, not raised; dorsal surface with regions clearly demarcated; frontal median triangle absent (Figs
Carapace broader than long, not raised; dorsal surface gently convex, regions clearly demarcated, covered with very short setae which does not obscure surface; frontal margin almost straight, without distinct median concavity, not deflexed, approx. a third carapace width; frontal median triangle absent (Figs
Mandibular palp 2-segmented, terminal one distinctly bilobed. Third maxilliped covering majority of buccal cavity when closed; ischium subrectangular, distinctly longer than broad, with shallow submedian groove; merus quadrate, slightly broader than long; exopod long, slender, reaching median part of merus, flagellum long, exceeding width of merus (Fig.
Chelipeds asymmetrical, right larger; surface of merus slightly rugose, relatively long, trigonal in cross section, margins without teeth or spines; carpus surface distinctly rugose, subovate, inner distal angle with sharp spine with basal tubercle; palm relatively stout, longer than broad, outer surface slightly rugose to almost smooth; fingers subequal in length to palm, dactylus marginally longer than pollex, curving inwards, cutting margin of fingers lined with numerous denticles, fingers pitted (Figs
Ambulatory legs not prominently elongate, third pair longest, fourth leg shortest; segments laterally flattened laterally, surfaces mildly rugose; dorsal margin of merus gently serrated, no visible subdistal tooth; carpus of first to third legs with low median ridge, absent on carpus of fourth leg; margins of propodus and dactylus lined with numerous short spines (Figs
Thoracic sternum surface evenly pitted to smooth; sternites 1 and 2 completely fused forming triangular structure; suture separating sternites 2 and 3 relatively shallow, sinuous, medially convex with lateral parts concave (towards buccal cavity); sternites 3 and 4 completely fused; sternopleonal cavity almost reaching imaginary line joining anterior edges cheliped coxae, near suture between sternites 2 and 3; part of sternite 8 exposed when pleon closed; tubercle of male pleonal locking mechanism prominent, peg-like, on anterior third of sternite 5 (Fig.
Pleon distinctly T-shaped; somite 1 short, broad, reaching coxae of fourth ambulatory legs; somite 2 slightly longer than somite 1, as broad as somite 1; somite 3 short, broadest, with prominently convex lateral margins; somites 4 and 5 trapezoidal; somite 5 notably narrower than 4, trapezoidal with concave lateral margins; somite 6 rectangular, slightly more than twice as long as broad, lateral margins concave; telson triangular, longer than broad, tip rounded (Fig.
Unlike the male holotype (the largest specimen), the degree and extent of the setation on the fingers of the chelae of the two smaller paratype males are the same in both chelipeds. Male specimens less than 15 mm in carapace width do not have the setae on the fingers of the chelae. The outer surface of the chela in smaller specimens is also relatively more rugose compared to larger ones.
The name is derived from the Latin
In life, the carapace is mostly dark reddish brown; the sub-branchial regions, third maxillipeds, pleon and thoracic sternum is pale yellow; the ambulatory legs dark brown, faintly marmorated, with exception of pale yellow, faintly spotted merus; and the chelipeds are yellowish orange, with the inner surfaces paler and the setose patches on the surface of the male fingers light brown (Fig.
In the general form of the carapace (not raised and relatively low) and relatively shorter ambulatory legs,
Two other species of
Holotype: male (14.0 × 12.0 mm) (
In life, the carapace is reddish brown with the ambulatory legs lighter in colour; the chelipeds are orangish red with the fingers pale-yellow (Fig.
The present series of specimens do not change the original description of this species in any way. The species does grow substantially larger than the type series, with the largest specimen here, a female measuring 26.1 × 21.3 mm (
The available collection data indicates
Holotype: male (17.6 × 13.3 mm) (
The live coloration of this species observed in the recent pair of specimens is a uniform dark purple colour on the dorsal surface of the carapace, ambulatory legs and chelipeds, with a pale purple to dull white on the thoracic sternum, pleon and distal portions of the ambulatory legs and cheliped fingers (Fig.
Habitat and life colour of
The biology of species of
Two individuals of
The biology of obligate arboreal crabs has been discussed at length by
Holotype male (29.2 × 20.4 mm) (
The freshly dead type specimen was described as dark brown overall (
The species was described from just outside the Danum Valley Conservation Area by
Holotype: male (40.0 × 30.0 mm) (
Fresh specimens have an olive-brown carapace with the grooves and striae reddish brown; the ambulatory legs are brown with specks of reddish brown; and the chelipeds are orange, with the fingers black except for the orange tip (Fig.
The recently collected specimens agree well with the published descriptions and figures of the species, originally described from Gomantong, Bettontan and Lahad Datu in Sabah (
Holotype: male (44.3 × 33.3 mm) (
The colour in life is dark green overall (H.H. Tan, pers. comm.).
Holotype: male (14.8 × 14.6 mm) (
The holotype of
1 | Third maxillipeds forming median rhomboidal gap when fully closed; carapace frontal margin with 4 distinct truncate lobes; cornea large, appearing bulbous in life; frontal and lateral surfaces of carapace with net-like pattern of short setae; exopod of third maxilliped without flagellum; terrestrial species |
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– | Third maxillipeds closing without any median rhomboidal gap; carapace frontal margin entire with 2 weakly separated rounded lobes; eyes not swollen in life; frontal and lateral surfaces of carapace may be granular but never with net-like pattern of short setae; exopod of third maxilliped with distinct flagellum; terrestrial and aquatic species |
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2 | Anterolateral margin of carapace with 3 well-defined, sharp teeth (including external orbital tooth) |
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– | Anterolateral margin of carapace rounded or straight, entire or with at most one tooth (external orbital tooth) |
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3 | Frontal margin and orbits of carapace appears sunken in from dorsal view; ambulatory legs very elongate, longest leg 4–5 times longer than carapace length; lives in tree-holes |
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– | Frontal margin and orbits of carapace level with sides from dorsal view; ambulatory legs proportionately much shorter; free-living |
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4 | Anterolateral carapace margin with a distinct epibranchial tooth clearly separated from external orbital tooth by V-shaped notch; |
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– | Anterolateral carapace margin appears entire or with a low epibranchial tooth barely separated from external orbital tooth; |
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5 | Carapace relatively flat, not prominently raised; gastric regions with distinct transverse striae; fingers of adult male chelipeds with dense mat of short setae; mostly aquatic species |
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– | Carapace prominently raised, appears swollen; gastric regions appears smooth, without prominent transverse striae; fingers of adult male chelipeds granulated, without setae; terrestrial to semiterrestrial species |
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6 | Carapace almost squarish to slightly rectangular; |
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– | Carapace transversely ovate, egg-shaped; |
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The authors would like to thank Dennis Sim, Marcus Ng, and Seawei Ying for permission to use their photographs of