Geosesarma pontianak, Ng, Peter K. L., 2015

Ng, Peter K. L., 2015, Semiterrestrial crabs of the genus Geosesarma De Man, 1892 (Crustacea, Brachyura, Sesarmidae) from western Borneo, Indonesia, with descriptions of three new species, Zootaxa 4048 (1), pp. 37-56 : 48-55

Geosesarma pontianak sp. nov.

( Figs. 11–13 )

Material examined. Holotype: male (13.4 × 13.2 mm) ( MZB Cru 4392), Gunung Kloncet, near km 67 milestone to Pontianak , on Pontianak to Anjungan Road, Kampung Anjungan, 00°21.02’N 109°11.08’E, Kabupaten Pontianak , West Kalimantan, coll. native collectors, through dealer, September 1999. Paratypes: 12 males, 12 females ( MZB Cru 4393), 123 males (largest 13.9 × 13.7 mm, smallest 6.3 × 6.2 mm), 69 females (largest 12.6 × 12.5 mm, smallest mature 8.2 × 8.1 mm), 3 ovigerous females ( ZRC 2015.0454), same data as holotype; 23 males (largest 13.7 × 13.4 mm), 19 females (largest 14.5 × 14.2 mm), 3 ovigerous females ( ZRC 2015.0455), Anjungan, Pontianak , Kabupaten Pontianak , West Kalimantan, coll. native collectors, from Singapore aquarium, 25 September 1999. Non-types: 4 males (largest 13.4 × 13.0 mm), 6 females (largest 13.4 × 12.6 mm) ( ZRC 2015.0456), Pontianak , Mandor area, near Anjungan, coll. local collectors, 31 August 1999; 1 female (10.1 × 9.6 mm) ( ZRC 2015.0457), near Anjungan, Kalimantan Barat, coll. H.H. Tan & Y.Y.Goh, 29 April 1998; 1 young male (7.6 × 7.3 mm) ( ZRC 2015.0458), near Anjungan, Kalimantan Barat, coll. H.H. Tan & Y.Y.Goh, 28 April 1998.

Diagnosis. Carapace almost square, width to length ratio 1.01–1.02, lateral margins subparallel ( Fig. 11 A, B); dorsal surface with well-defined regions, anterior regions covered with small rounded, flattened granules ( Fig. 11 B); front deflexed, frontal lobes broad with gently convex margins; postfrontal, postorbital cristae prominent, very sharp, strong ( Fig. 11 B, C); external orbital tooth triangular, outer margins curving anteriorly, tooth directed anteriorly, not extending past lateral margin ( Fig. 11 B). Merus of third maxilliped subovate, subequal in length to ischium; exopod without trace of flagellum ( Fig. 13 A). Outer surface of palm of adult male covered with small rounded granules; dorsal margin of dactylus with 11 or 12 tubercles (distal one smallest), each with pectinated tip ( Fig. 11 E, F). Ambulatory legs with relatively slender merus, with sharp subdistal spine on dorsal margin, surfaces slightly rugose ( Figs. 11 A, 13C). Male abdomen broadly triangular; somite 6 relatively broad, with gently convex lateral margins; telson semicircular ( Figs. 11 D, 12, 13B). G1 relatively stout, subdistal part of outer margin with distinct right-angled angled, prominent hump-like arch just before distal pectinated part; pectinated distal part elongate from lateral view, subspatuliform from marginal view, with small median cleft ( Fig. 13 D–H, J, K, M).

Colour. The adult colours and patterns of G. pontianak sp. nov. are similar to those of G. ambawang sp. nov. ( Fig. 10 ).

Etymology. In Indonesian mythology, a “ Pontianak ” is a vampiric ghost. The name of the new species alludes to its eerie-looking yellow eyes and is also in reference to the type locality, the district of Pontianak . The name is used as a noun in apposition.

Ecology. According to local collectors (P. Yap, pers. comm.), the species was collected in the forest near small streams.

Remarks. Most of the species now known from Borneo do not have a flagellum on the exopod of the third maxilliped. The only three species that have this flagellum, G. amphinome and G. pylaemenes sp. nov. and G. sarawakense , are also characterised by possessing a more trapezoidal carapace with the lateral margins diverging ( Figs. 1 A, B, 2A, 3A, B, 5A, B, 6A, B; Serène 1968). The remaining species from Borneo all have distinctly quadrate carapaces which are only slightly longer than wide.

Geosesarma ambawang sp. nov. and G. pontianak sp. nov. are each other’s closest relative, possessing the same colour pattern in life, as well as similar third maxilliped and G1 structures. Geosesarma ambawang sp. nov., however, differs in the following aspects: carapace proportionately wider (width to length ratio 1.06–1.08, Fig. 8 B) (1.01–1.02 in G. pontianak sp. nov., Fig. 11 B), the external orbital tooth is directed obliquely laterally ( Fig. 8 A, B) (curving anteriorly in G. pontianak sp. nov., Fig. 11 A, B), the postfrontal and postorbital cristae are distinct but not very sharp ( Fig. 8 A–C) (very sharp and strong in G. pontianak sp. nov., Fig. 11 A–C), the ambulatory meri are proportionately shorter and stouter ( Figs. 8 A, 9C) (relatively longer and more slender in G. pontianak sp. nov., Figs. 11 , 13 C), the male abdomen is proportionately narrower, especially somite 6, with the telson relatively shorter ( Fig. 8 D, 9B) (proportionately wider with a wide somite 6 and longer telson in G. pontianak sp. nov., Figs. 11 D, 12, 13B), the subterminal hump on the G1 is distinct but more sloping ( Fig. 9 D–H) (usually sharply right-angled in G. pontianak sp. nov., Fig. 13 D–H, J, K, M). The angle of the hump in G. pontianak sp. nov. varies slightly, and may be less distinctly right-angled, especially in smaller specimens (e.g., Fig. 13 L). In such cases, the G1 of G. pontianak sp. nov. and G. ambawang sp. nov. are almost indistinguishable. The two species, however, can still be easily distinguished by the form of the carapaces (more quadrate in G. pontianak sp. nov.) and ambulatory legs (more slender and relatively longer in G. pontianak sp. nov.).

The three species currently known from Sabah, G. aurantium , G. danumense and G. sabanum are distinct from G. ambawang sp. nov. and G. pontianak sp. nov. in that the dorsal margin of the dactylus of the adult male chela has only low proximal granules and not a row of tubercles (cf. Ng 1992: fig. 1D; Ng 1995a: fig. 1C; Ng 2002: fig. 2b). In G. ambawang sp. nov., the dactylus has 11 or 12 such tubercles on the dorsal margin ( Fig. 8 E, F), whereas G. pontianak sp. nov. has 12 or 13 tubercles ( Fig. 11 E, F). Geosesarma aurantium (southern Sabah) differs from G. ambawang sp. nov. and G. pontianak sp. nov. in having a less developed frontal margin with the external orbital teeth more acutely triangular in shape (cf. Ng 1995a: fig. 1A), anterior parts of the dorsal surface of the carapace is relatively less granular (cf. Ebin & Chung 2012), the ambulatory legs are proportionately much shorter (cf. Ng 1995a: fig. 1E, F), the male telson is recessed in the broad distal margin of somite 6 (cf. Ng 1995a: fig. 1H), and the distal pectinated part of the G1 is spatuliform and flared (cf. Ng 1995a: fig. 3). Geosesarma danumense (central Sabah) differs from G. ambawang sp. nov. in having the anterior dorsal carapace surface distinctly less strongly granular (cf. Ng 2002: fig. 1a, b), an external orbital tooth that is broadly triangular (cf. Ng 2002: fig. 1a, b, 3A), the ambulatory meri are more slender and relatively longer (cf. Ng 2002: fig. 1a, 3B), the male telson is recessed in the distal margin of somite 6 (cf. Ng 2002: fig. 2c, 3C), and the G1 is proportionately more slender, with the distal pectinated part spatuliform with a subdistal projection (cf. Ng 2002: fig. 3D–H). Geosesarma pontianak sp. nov. differs from G. danumense in all these characters as well, except that the ambulatory legs are similar in length ( Figs. 11 A, 13C versus Ng 2002: figs. 1a, 3B). Geosesarma sabanum (from eastern Sabah) differs from G. ambawang sp. nov.

in having an external orbital tooth that is more acutely triangular and separated from rest of the margin by a low indentation, not by a cleft (cf. Ng 1992: fig. 1A), and the G1 has a short subdistal projection (cf. Ng 1992: fig. 1G, I, J). Geosesarma pontianak sp. nov. also differs from G. sabanum in these characters except that its ambulatory legs are proportionately longer ( Figs. 11 A, 13C versus Ng 1992: fig. 1C). The colour of G. aurantium is strikingly different from G. ambawang sp. nov., being bright yellowish-orange in life (Ng 1995a; Ebin & Chung 2012). The carapace of G. danumense is orangish-brown in life, with the legs purplish brown and the chelae white (unpublished data). The live colour of G. sabanum is not known.

Like G. ambawang sp. nov. ( Fig. 8 E, F) and G. pontianak sp. nov. ( Fig. 11 E, F), the three species from Sarawak, G. b a u, G. gracillimum and G. katibas all have 9–11 tubercles on the dorsal margin of the dactylus of the male chela ( Fig. 14 E, F; Ng & Grinang 2004: 320; Ng 1995b: figs. 11C, D, 13A). Geosesarma bau (from western Sarawak) differs from G. ambawang sp. nov. in having ambulatory legs that are proportionately longer (cf. Ng & Grinang 2004: fig. 8A, B), and the G1 is proportionately more slender without any subdistal hump, with the distal pectinated part only gently bent and subcylindrical in shape (cf. Ng & Grinang 2004: fig. 9D–F). Geosesarma pontianak sp. nov. resembles G. b a u in the proportions of the ambulatory legs, but its external orbital tooth is directed anteriorly with the outer margins curving anteriorly ( Fig. 11 A, B) (directed obliquely with the outer margin gently convex in G. b a u, Ng & Grinang 2004: fig. 9A, B); and the G1 is relatively much stouter with a distinct subdistal hump ( Fig. 13 D–H, J–M) (slender without a subdistal hump in G. bau, Ng & Grinang 2004 : fig. 9D–F). Geosesarma gracillimum (northern Sarawak and Brunei) can be distinguished from G. ambawang sp. nov. in having a more distinctly quadrate carapace, the ambulatory legs are proportionately longer and male abdominal somite 6 is relatively wider ( Fig. 14 A, B, D). Most significantly, the G1 of G. gracillimum differs markedly from G. ambawang sp. nov. and G. pontianak sp. nov. in that it has no subdistal hump, with the distal pectinated part subcylindrical and tapering to subtruncate tip (cf. Holthuis 1979: fig. 9b, c; Ng 1995b: fig. 13B–E). Geosesarma katibas (Lanjak-Lantimau, central Borneo) can be separated from G. ambawang sp. nov. in having an external orbital tooth that is more acutely triangular in shape (cf. Ng 1995b: fig. 9, 11A), the anterior carapace regions are more prominently granular (cf. Ng 1995b: fig. 9), the ambulatory meri and propodi are longer (cf. Ng 1995b: fig. 9, 11F), the merus of the third maxilliped is shorter than the ischium (cf. Ng 1995b: fig. 11B), and the G1 has no subdistal hump, with the distal pectinated part subcylindrical and tapering (cf. Ng 1995b: fig. 12A–E). These differences are also applicable for G. pontianak sp. nov., except that their ambulatory legs do not differ in proportions ( Figs. 11 A, 13C; Ng 1995b: fig. 9, 11F), and in G. katibas , the male abdomen, notably somite 6, is proportionately narrower (cf. Ng 1995b: fig. 11G versus Figs. 10 D, 12B). The live colour of G. gracillimum is quite different from that of G. ambawang sp. nov. and G. pontianak sp. nov., being a relatively uniform reddish-brown to red, including the chelae (unpublished data), whereas G. katibas has a reddish-brown carapace, with the palms of the chela purple and the fingers orange (cf. Ng 1995b: fig. 10). Live G. bau have an orangish-red carapace, with the chelae and legs brown (unpublished data).

Geosesarma ambawang sp. nov. and G. pontianak sp. nov. also resemble G. notophorum Ng & Tan, 1995 , and G. r a j Schubart & Ng, 2014, from Pulau Lingga and Pulau Bintan in the Riau Islands off Sumatra, respectively. Both species also lack a flagellum on the exopod of the third maxilliped. Geosesarma raj , however, can be separated from G. ambawang sp. nov. in having frontal lobes that are more truncated in shape from the dorsal view (cf. Schubart & Ng 2014: fig. 1B, D), the external orbital tooth is more acutely triangular and anteriorly directed (cf. Schubart & Ng 2014: fig. 1B, D), the dorsal margin of the dactylus of the chela has only 8 or 9 tubercles (cf. Schubart & Ng 2014: fig. 2D), the ambulatory merus is relatively longer and more slender (cf. Schubart & Ng 2014: fig. 1B, 3D), and the distal pectinated part of the G1 is subcylindrical and tapering (cf. Schubart & Ng 2014: fig. 3J–M). Its live colour also differs slightly, with the carapace being greyish and the chelae are uniformly reddish-orange ( Schubart & Ng 2014: fig. 4). Geosesarma pontianak sp. nov. is similar to G. r a j in the structure of the external orbital teeth and ambulatory leg proportions ( Fig. 11 A, B, 13C) but the carapace of G. r a j is relatively broader (width to length usually 1.07–1.10) with the postorbital and postfrontal cristae not as strong (cf. Schubart & Ng 2014: fig. 1B, D); male abdominal somite 6 is proportionately less broad ( Schubart & Ng 2014: fig. 3F) (much wider in G. pontianak sp. nov., Figs. 11 D, 12, 13B); and the subterminal hump of the G1 is gently sloping ( Schubart & Ng 2014: fig. 3J–M) (at right angles G. pontianak sp. nov., Fig. 13 D–H, J, K, M). The carapace shape, proportions, structures of the postfrontal and postorbital cristae, as well as the external orbital tooth of G. notophorum (cf. Ng & Tan 1995: pl. 1, fig. 1A) are similar to those of G. ambawang sp. nov. ( Fig. 8 A, B) (width to length ratios 1.05-1.10 and 1.06–1.08, respectively). This is in contrast to the carapace of G. pontianak sp. nov., which is distinctly more quadrate (width to length ratio 1.01–1.02), the postfrontal and postorbital cristae are much sharper and more prominent, and the external orbital tooth is broader and directed anteriorly ( Fig. 11 A, B). The ambulatory legs are relatively short in G. ambawang sp. nov. ( Figs. 8 A, 9C), but are proportionately longer in G. notophorum (cf. Ng & Tan 1995: pl. 1, fig. 1F) and G. pontianak sp. nov. ( Figs. 11 A, 13C). The male telson of G. notophorum is distinctly more triangular (cf. Ng & Tan 1995: fig. 1C) than that of G. ambawang sp. nov. (or G. pontianak sp. nov. (relatively broader and more rounded in these two species, Figs. 8 D, 9B, 11D, 13B). The proportions of the male abdominal somite 6 of G. notophorum (cf. Ng & Tan 1995: fig. 1C), however, are similar to that of G. ambawang sp. nov. ( Fig. 9 B), with both being proportionately less broad than that of G. pontianak sp. nov. ( Fig. 13 B). Most significantly, the G1 of G. notophorum does not have a distinct subdistal hump, being gently sloping and the distal pectinated part is more tapering (cf. Ng & Tan 1995: fig. 1H–J), in sharp contrast to those of G. ambawang sp. nov. and G. pontianak sp. nov., which have a distinct hump, being usually distinctly right-angled in the latter species ( Figs. 9 D–H, 13D–H, J, K, M). The carapace G. notophorum is also evenly pale brown to purplish-brown in life, with the posterior half usually darker (Ng & Tan 1995: 394, pl. 1).

In live coloration, G. ambawang sp. nov. and G. pontianak sp. nov. resemble G. bicolor Ng & Davie, 1995 (western Java), which was described as bright purple on the anterior third of the carapace and ambulatory legs, with the posterior parts of the carapace bluish-grey; the chelae red and eyes bright yellow (Ng & Davie 1995: 32). The ambulatory legs of G. b i c o l o r, however, are distinctively shorter than either species (Ng & Davie 1995: fig. 1). While the carapace of G. b i co l o r superficially resembles G. ambawang sp. nov. and G. pontianak sp. nov., the exopod of the third maxilliped of G. b i co l o r has an elongated flagellum (cf. Ng & Davie 1995: fig. 2C), the male abdomen is proportionately broader (cf. Ng & Davie 1995: fig. 2F; Ng et al. 2015: fig. 2J), and the G1 is slender with an elongated pectinated distal part (cf. Ng & Davie 1995: fig. 2G, I–M; Ng et al. 2015: fig. 2F–I). Geosesarma dennerle Ng, Schubart & Lukhaup, 2015 (central Java) has a bi-coloured carapace, but in this species, the carapace colour is a much brighter purple and the chelae are also bright purple, not red or orange (cf. Ng et al. 2015: fig. 6A– C).

The aquarium trade has been exporting many species of Geosesarma to Europe, but the identities of these have always been dubious, partly because of their unknown provenance (see Rademacher & Mengedoht 2011). One species worth noting is what has been called “ Geosesarma notophorum Mandarinkrabbe ” by the German aquraium trade ( Rademacher & Mengedoht 2011: 42). These specimens, which have been imported into Germany since 2006 (possibly earlier), bear a close resemblance in their colour pattern to what is here described as G. pontianak sp. nov. in their colour pattern. Although they were reportedly collected from the type locality in Pulau Lingga, this seems unlikely as this location is not easily accessible. Pontianak , on the other hand has several major aquarium dealers in the city, and they regularly export freshwater fish from western Borneo. It seems more likely that the collectors in Pontianak , who obtained the present specimens from Anjungan for the trade, had and continue to export material to Europe.

Geosesarma notophorum is known to possess a novel method of caring for its newly hatched juveniles by carrying them on its carapace (Ng & Tan 1995). This behaviour is now known for several species that also practice direct development. The eggs of G. ambawang sp. nov. are large, and indicate that they hatch directly into juvenile crabs, and possibly behave the same way as G. notophorum . If the material exported into Germany as “ Geosesarma notophorum Mandarinkrabbe ” is indeed what is here described as G. pontianak sp. nov. (see above), then it also possesses the same brood care method as G. notophorum s. str. (O. Mengedoht, pers. comm.).

Figures

FIGURE 1. Geosesarma amphinome (De Man, 1899). A, lectotype female (11.1 × 8.5 mm) (NNM 1198), Sintang, Borneo; B – F, paralectotype male (14.4 × 8.7 mm) (NNM 23283), Sintang, Borneo. A, B, overall habitus; C, dorsal view of anterior part of carapace; D, frontal view of carapace; E, male abdomen; F, outer view of left chela. (B – F after De Man 1899: pl. 12 fig. 16).

FIGURE 8. Geosesarma ambawang sp. nov., holotype male (11.5 × 10.7 mm) (MZB Cru 4390), Pontianak, Kalimantan Barat, Borneo. A, overall habitus; B, dorsal view of carapace; C, frontal view of cephalothorax; D, ventral view of cephalothorax showing thoracic sternum and abdomen; E, F, outer view of right chela.

FIGURE 9. Geosesarma ambawang sp. nov., holotype male (11.5 × 10.7 mm) (MZB Cru 4390), Pontianak, Kalimantan Barat, Borneo. A, left third maxilliped; B, male abdominal somites 1 – 6 and telson; C, left second ambulatory leg; D, left G 1 (ventral view); E, left G 1 (ventral view); F, distal part of left G 1 (ventral view); G, distal part of left G 1 (dorsal view); H, distal part of left G 1 (subdorsal view); I, J, distal part of left G 1 (mesial view); K, left G 2. All structures (except C) denuded. Scales: A – E, K = 1.0 mm; F – J = 0.5 mm.

FIGURE 10. Geosesarma ambawang sp. nov., colours in life. A, B, non-type male (12.5 × 11.8 mm); C, D, specimens climbing shrubs in situ. Specimens not preserved, photographs by Y. Kho.

FIGURE 11. Geosesarma pontianak sp. nov., holotype male (13.4 × 13.2 mm) (MZB Cru 4392), Anjungan, Kalimantan Barat, Borneo. A, overall habitus; B, dorsal view of carapace; C, frontal view of cephalothorax; D, ventral view of cephalothorax showing thoracic sternum and abdomen; E, F, outer view of left chela.

FIGURE 12. Geosesarma pontianak sp. nov., Anjungan, Kalimantan Barat, Borneo. Male abdomens. A, paratype male (11.4 × 10.0 mm) (ZRC 2015.0454 a); B, paratype male (13.2 × 13.0 mm) (ZRC 2015.0454 b); C paratype male (11.1 × 10.8 mm) (ZRC 2015.0454 c).

FIGURE 13. Geosesarma pontianak sp. nov., Anjungan, Kalimantan Barat, Borneo. A – I, holotype male (13.4 × 13.2 mm) (MZB Cru 4392); J, K, paratype male (13.2 × 13.0 mm) (ZRC 2015.0454 a); L, paratype male (11.4 × 10.0 mm) (ZRC 2015.0454 b); M, paratype male (11.1 × 10.8 mm) (ZRC 2015.0454 c). A, left third maxilliped; B, male abdomen; C, left second ambulatory leg; D, J, L, left G 1 (ventral view); E, left G 1 (dorsal view); F, K, M, distal part of left G 1 (ventral view); G, distal part of left G 1 (dorsal view); H, distal part of left G 1 (subdorsal view); I, left G 2. All structures (except C) denuded. Scales: A – C, D, E, I, J, L = 1.0 mm, F – H, K, M = 0.5 mm.

FIGURE 14. Geosesarma gracillimum (De Man, 1902), male (12.1 × 11.8 mm) (ZRC 2007.262), Lambir National Park, Sarawak, Malaysia Sarawak, Malaysia. A, overall habitus; B, dorsal view of carapace; C, frontal view of cephalothorax; D, ventral view of cephalothorax showing thoracic sternum and abdomen; E, F, outer view of left chela.