Geosesarma foxi ( Kemp, 1918 )

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 : 227-232

publication ID	https://doi.org/ 10.5281/zenodo.5356013
publication LSID	lsid:zoobank.org:pub:94DDC8A4-4575-4331-9DBF-4A2494D79A6F
persistent identifier	https://treatment.plazi.org/id/03F0A828-FFBF-FF97-A61C-0EB17E09FCC0
treatment provided by	Valdenar
scientific name	Geosesarma foxi ( Kemp, 1918 )
status

Treatment

Geosesarma foxi ( Kemp, 1918) View in CoL

( Figs. 1–5 View Fig View Fig View Fig View Fig View Fig , 7A–H View Fig )

Sesarma foxi Kemp, 1918: 238 View in CoL , figs. 3, 4. Sesarma (Geosesarma) foxi View in CoL – Serène, 1968: 107. Geosesarma foxi View in CoL – Serène & Soh, 1970: 407; Ng & Ng, 1987: 13;

Ng, 1988: 122, fig. 54; Ng, 2004: 333 (list); Ng & Yeo, 2007:

115 (list); Ng et al., 2008: 220 (list).

Material examined. 1 male (11.4 × 11.0 mm) ( ZRC 2016.0598 View Materials ), ca. mid-way Tangga Helang Seribu Kenangan hiking trail from base to just before summit of Gunung Raya , Langkawi Island, Peninsular Malaysia, coll. R.-M. Low, 16 July 2016 ; 3 males (11.5 × 11.4 mm, 9.6 × 9.7 mm, 7.8 × 7.7 mm), 3 females (11.8 × 11.9 mm, 7.5 × 7.3 mm, 6.8 × 6.7 mm) ( ZRC 2016.619 View Materials ), near start of Tangga Helang Seribu Kenangan hiking trail from below summit of Gunung Raya , Langkawi Island, Peninsular Malaysia, ca. 780 m asl, coll. J.-J. Li, 31 December 2016 ; 4 males (10.9 × 10.9 mm, 9.9 × 10.0 mm, 8.0 × 7.9 mm, 6.6 × 6.7 mm), 1 ovigerous female (11.7 × 11.8 mm), 3 females (10.8 × 10.9 mm, 8.6 × 8.4 mm, 8.2 × 8.1 mm) ( ZRC 2016.618 View Materials ), near start of Tangga Helang Seribu Kenangan hiking trail from below summit of Gunung Raya , Langkawi Island, Peninsular Malaysia, ca. 780 m asl, coll. P.Y.C. Ng, 12–13 January 2017 .

Diagnosis. Carapace quadrate, slightly wider than long or subequal, adult width to length ratio 1.00–1.04, lateral margins parallel ( Figs. 1A View Fig , 3A–C View Fig , 4 View Fig ); dorsal surface with regions just visible, anterior regions with small rounded granules on gastric regions ( Figs. 3A–C View Fig , 4 View Fig ); front distinctly deflexed, frontal lobes broad with gently convex margins in dorsal view; postfrontal, postorbital cristae sharp, distinct ( Figs. 3B–D View Fig , 4 View Fig ); 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 cleft ( Figs. 3B, C View Fig , 4 View Fig ). Merus of third maxilliped subovate, shorter than ischium; exopod slender with no trace of flagellum ( Fig. 7A View Fig ). 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 7 or 8 low, non-chitinous tubercles on proximal half ( Figs. 1B View Fig , 3A View Fig , 4A, B View Fig , 5D View Fig ). Ambulatory legs with long, slender merus, with sharp subdistal spine on dorsal margin, surfaces gently rugose ( Figs. 1A View Fig , 3A View Fig , 4A, B View Fig ). Male pleon broadly triangular; somite 6 wide, with convex lateral margins; telson almost semicircular, not recessed into distal margin of somite 6 ( Fig. 5A–C View Fig ). G1 slender; outer margin of subdistal part of subterminal segment (in ventral view) with distinct shelf-like angle ( Fig. 7B–E View Fig ), distal chitinous part elongated, distal part gently curved, tip spatuliform ( Fig. 7B–G View Fig ).

Females. Females resemble males in all non-sexual characters, with the chelae equal, relatively slenderer and less inflated ( Fig. 4B View Fig ). 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. 5E View Fig ). The vulvae on thoracic sternite 6 are large, positioned closer to suture with sternite 5, with an operculum and a large truncate vulvar process which arches over the opening ( Fig. 5F View Fig ). One female (11.7 × 11.8 mm, ZRC 2016.618) had several subovate eggs still under its pleon, with each measuring ca. 1.5 mm in diameter.

Variation. The carapace proportions vary slightly, with smaller males and females sometimes appearing slightly more trapezoidal in shape, with the lateral margins slightly diverging (e.g., Fig. 4B View Fig ). The second lateral tooth (after the external orbital tooth) is always distinct, although it may vary in size ( Figs. 3B, C View Fig , 4C, D View Fig ), and demarcated from the rest of the margin by a wide cleft. Smaller males (less than 7 mm carapace width) also have slender, equal chelae; and the G1, while resembling those of adults, are relatively straighter and poorly chitinised.

Colour. Kemp (1918: 240) described his fresh specimens of G. foxi as follows: “the carapace of the specimens is of a very dull reddish brown; the chelipedes are pale yellow suffused with pale red on the carpus and palm; the walking legs are deep brown with a fine mottling and dark chromatophores are thickly sprinkled on the abdomen.” The series of specimens on hand essentially confirm his observations. In live specimens, the anterior half of the carapace (from the H-shaped gastrocardiac groove) as well as the chelipeds are deep orange to almost red ( Fig. 2 View Fig ). The intensity of the colour varies only slightly. The posterior half of the carapace and ambulatory legs vary from light brown to purplish black, and covered with numerous small white or light blue spots ( Fig. 2 View Fig ). The frontal surfaces of the cephalothorax and thoracic sternum are deep orange ( Fig. 2B View Fig ), while the abdomen is orange with numerous small dark brown spots and mottling.

Taxonomic remarks. Kemp (1918: 240) described the species from two males measuring 9.8 × 9.8 mm and 9.7 × 9.8 mm, without specifying a holotype. Ng (1988: 122) designated the slightly larger male in the Zoological Survey of India in Calcutta as the lectotype of Sesarma foxi Kemp, 1918 . For comparisons with G. serenei and G. faustum n sp., see remarks for the latter species.

Sympatric taxa. Three other species of freshwater crabs occur on Gunung Raya. The semiterrestrial potamid Stoliczia bella Ng & Ng, 1987 , is found in or near permanent water bodies from near the base to about 700 m asl on Gunung Raya. At the base of Gunung Raya, the fully aquatic gecarcinucid Siamthelphusa improvisa ( Lanchester, 1902) is common in shallow streams with vegetation. The gecarcinucid Phricotelphusa gracilipes Ng & Ng, 1987 , is found in most of the streams and springs around the mountain, and even occurs in the forest floor and summit, sometimes far from permanent water sources. The author has also found it in piles of moist decaying leaves along the same trail where G. foxi was collected.