Geosesarma serenei Ng, 1986

Ng, Peter K. L., 2017, On the identities of the highland vampire crabs, Geosesarma foxi (Kemp, 1918) and G. serenei Ng, 1986, with description of a new phytotelmic species from Penang, Peninsular Malaysia (Crustacea: Decapoda: Brachyura: Sesarmidae), Raffles Bulletin of Zoology 65, pp. 226-242 : 232-235

Geosesarma serenei Ng, 1986

( Figs. 6 , 7I–P )

Sesarma ? maculata – Lanchester, 1902: 550 (not Sesarma maculata De Man, 1892 )

Sesarma (Sesarma) foxi – Tweedie, 1936: 52 (not Sesarma foxi Kemp, 1918 ).

Sesarma foxi – Tweedie, 1940: 108, fig. 11 (not Sesarma foxi Kemp, 1918 ).

Geosesarma serenei Ng, 1986a: 6 , fig. 2; Ng, 1988: 124, figs. 53A, 55; Ng, 2004: 333 (list); Ng & Yeo, 2007: 115 (list); Ng et al., 2008: 220 (list).

Material examined. Holotype: male (8.3 × 8.2 mm) ( ZRC 1964.9.8.1), Bukit Larut , Maxwell Hill, 4°47′N 100°45′E, Perak, Peninsular Malaysia, ca. 1150 m, coll. H.M. Pendlebury, February 1932 . Paratype: ovigerous female (10.4 × 9.7 mm) ( ZRC 1964.9.8.2), same data as holotype. Others : 1 young male (7.0 × 6.9 mm), 1 female (7.4 × 7.1 mm) ( ZRC 2003.64 ), Bukit Larut , Maxwell Hill , beyond Gunung Hijau Resthouse, 4°47′N 100°45′E, Perak, Peninsular Malaysia, ca. 1150 m, at night, coll. T.M. Leong & G. Lim, 27 March 2003 .

Diagnosis. Carapace quadrate, slightly wider than long or subequal, adult width to length ratio 1.01–1.04, lateral margins parallel ( Fig. 6A, B, F ); dorsal surface with regions just visible, anterior regions with small rounded granules on gastric regions ( Fig. 6A, B, E, F ); front distinctly deflexed, frontal lobes broad with truncate margins in dorsal view; postfrontal, postorbital cristae sharp, distinct ( Fig. 6B, F ); external orbital tooth triangular, directed obliquely laterally, outer margin gently convex, tip not extending beyond lateral margin; second lateral tooth distinct, clearly separated from rest of margin by wide clef ( Fig. 6B, F ). Merus of third maxilliped subovate, shorter than ischium; exopod slender with no trace of flagellum (cf. Ng, 1988: fig. 55C). Outer surface of palm of adult male covered with small rounded granules and striae; inner surface granulated but without transverse ridge; dorsal margin of dactylus with 6 or 7 low, non-chitinous tubercles on proximal half ( Fig. 6A, D ). Ambulatory legs with long, slender merus, with sharp subdistal spine on dorsal margin, surfaces gently rugose ( Fig. 6A, E ). Male pleon broadly triangular; somite 6 wide, with convex lateral margins; telson almost semicircular, not recessed into distal margin of somite 6 ( Fig. 6C ). G1 slender; outer margin of subdistal part of subterminal segment (in ventral view) with gently sloping shelf-like area ( Fig. 7I, J ), distal chitinous part elongated, distal part almost straight, tip spatuliform ( Fig. 7I–L ).

Females. The adult female resembles the adult male in nonsexual characters, with the chelae equal, relatively slenderer and less inflated. The pleon is ovate, covering most of the thoracic sternum, with the telson broadly triangular with convex lateral margins and distinctly inserted into the distal margin of somite 6 ( Fig. 6G ). The vulvae on thoracic sternite 6 are relatively large, positioned closer to suture with sternite 5, with an operculum and a large truncate vulvar process which arches over the opening ( Fig. 6H ).

Variation. The few specimens on hand do not lend much for a discussion on their variation. Smaller specimens (7 mm carapace width, ZRC 2003.64) closely resemble the adult holotype male except that the second lateral tooth is relatively larger, the chelae are equal and slenderer ( Fig. 6E, F ). The G1 of this small male is weakly chitinised and clearly juvenile in form, and while it superficially resembles that of the adult, the distal part is almost straight and not chitinous ( Fig. 7N–P ).

Colour. The live colour of this species is not known, but probably similar to those of G. foxi and G. faustum n. sp. The small specimens of G. serenei (ZRC 2003.64) have the distinctive spots characteristic of the other two species.

Taxonomic remarks. In discussing differences with G. serenei, Ng (1988: 122) noted that the “subterminal segment of the G1 of G. foxi however, appears to be stouter and slightly shorter, and the terminal segment is also relatively shorter and the tip rounder. The two taxa may eventually prove conspecific when more specimens of both species become available, and the variations presently noted shown to be merely due to variation.” This comparison was based on the sketch of the G1 provided to him by the Zoological Survey of India ( Ng, 1988: fig. 54D). The present series of specimens of G. foxi show that this difference is not valid as it is now clear from examining the material that the G 1 in Ng (1988) had been drawn with the structure tilted at a slight angle, making it appear stouter than it actually is. There are, however, other characters that can separate the two species. For detailed differences with G. foxi and G. faustum n sp., see remarks for the latter species.

In recording G. serenei (as S. foxi ), Tweedie (1940: 108) commented that he had “ two adult males, two females and two juveniles from Lacom, Peninsular Siam [present day Thailand], collected by the ‘Skeat’ Expedition of 1899–1900 and erroneously determined as S. maculata de Man by Lanchester (l.c.). The two largest specimens of this series measure 11.7 (♂) and 11.0 (♀) mm. in anterior carapace breadth, and are the largest specimens of S. foxi so far recorded.” In describing G. serenei, Ng (1986a: 36) placed Lanchester’s (1902) and Tweedie’s (1936) material from Peninsular Thailand under the synonymy of the new species with doubt. Tweedie (1940: 108–109) notes that the locality “Lacom” given by Lanchester is difficult to interpret precisely. It probably refers to Lakon, which is an alternative name for Nakon Si Thammarat. Other records indicate that the species is montane in habit and the ‘Skeat’ specimens probably came from the hills a short distance inland from Nakon Si Thammarat, which range up to a height of over 1500 metres. The present author agrees with this interpretation. Material from Nakon Si Thammarat will need to be examined to ascertain if the species there is actually G. serenei or another taxon.

Sympatric taxa. Another species of Geosesarma , G. cataracta Ng, 1986 , also occurs on Bukit Larut, but lives at relatively lower altitudes among the mosses adjacent to waterfalls, possessing proportionately shorter and stouter ambulatory legs and a different G1 structure (see Ng, 1986a, 1988). Two species of potamids are present on Bukit Larut, Stoliczia tweediei ( Roux, 1934) and S. larutensis Ng & Schubart, 2014 . Stoliczia tweediei is a fully aquatic species and is present in the waterfalls at altitudes up to 900 m asl; while S. larutensis is semiterrestrial and lives in the damp forests of the summit, probably with G. serenei (see Ng, 1993; Ng & Schubart, 2014). One species of gecarcinucid, Phricotelphusa hockingi Ng, 1986 , occurs in the streams and waterfalls but apparently does not reach the summit ( Ng, 1986b, 1988).

Figures

Fig. 6. Geosesarma serenei Ng, 1986. A–D, holotype male (8.3 × 8.2 mm) (ZRC 1964.9.8.1); E, F, young male (7.0 × 6.9 mm) (ZRC 2003.64); G, H, paratype ovigerous female (10.4 × 9.7 mm) (ZRC 1964.9.8.2). All specimens from Bukit Larut, Perak. A, E, overall dorsal view; B, F, dorsal view of carapace; C, male pleon; D, outer view of left chela; G, female pleon; H, female sternopleonal cavity showing vulvae.

Fig. 7. A–H, Geosesarma foxi (Kemp, 1918), male (11.4 × 11.0 mm) (2016.0598), Gunung Raya, Langkawi; I–M, G. serenei Ng, 1986, holotype male (8.3 × 8.2 mm) (ZRC 1964.9.8.1), Bukit Larut, Perak; N–P, G. serenei Ng, 1986, young male (7.0 × 6.9 mm) (ZRC 2003.64), Bukit Larut. A, left third maxilliped (mostly denuded); B, I, N, left G1 (ventral view); C, J, left G1 (dorsal view); D, distal part of left G1 (ventral view); E, distal part of left G1 (dorsal view); F, K, O, distal part of left G1 (outer lateral view); G, L, P, distal part of left G1 (mesial view); H, M, left G2. Scales = 0.5 mm.