Geosesarma bintan, Schubart & Ng, 2014

Schubart, Christoph D. & Ng, Peter K. L., 2014, Two new species of land-dwelling crabs of the genus Geosesarma De Man, 1892 (Crustacea: Brachyura: Thoracotremata: Sesarmidae) from Bintan Island, Indonesia, Raffles Bulletin of Zoology 62, pp. 615-619 : 615-616

publication ID	https://doi.org/ 10.5281/zenodo.4504166
publication LSID	lsid:zoobank.org:pub:924CD2C9-3007-4321-81E2-0237EE1359BA
persistent identifier	https://treatment.plazi.org/id/BBABCEDE-E066-443F-86DC-9CA238032073
taxon LSID	lsid:zoobank.org:act:BBABCEDE-E066-443F-86DC-9CA238032073
treatment provided by	Carolina
scientific name	Geosesarma bintan
status	sp. nov.

Treatment

Geosesarma bintan View in CoL , new species

( Figs. 1A, C View Fig , 2A, C View Fig , 3A, C, E View Fig , G–I)

Material examined. Holotype – male (11.2 × 9.8 mm) ( MZB Cru 3813), Indonesia: Riau Archipelago, Bintan Island , near swampy lowland freshwater stream, 1°10'0"N, 104°23'0.6"E, coll. T.H. T. GoogleMaps

Tan et al., 11 May 1993. Paratype – male (9.7 × 8.5 mm) ( ZRC 2014.0284 View Materials ), same locality data as holotype .

Diagnosis. Carapace rectangular, distinctly wider than long, lateral margins gently diverging towards posterior carapace margin ( Fig. 1A, C View Fig ); dorsal surfaces generally smooth, except for rugose anterior regions; H-shaped median depression shallow; postfrontal cristae prominent, margins rounded; exorbital tooth triangular, directed obliquely, with additional low tooth behind it ( Figs. 1C View Fig , 2A View Fig ). Exopod of third maxilliped relatively slender, with long flagellum ( Fig. 3A View Fig ). Male chelae with long fingers, scattered granules, rugosities on dorsal and ventral surfaces of palm, as well as on proximal part of dactylus; dorsal margin of dactylus with 5 or 6 low, rounded granules on proximal half ( Fig. 2C View Fig ). Ambulatory legs with relatively broad meri, with sharp subdistal spine on dorsal margin, surface gently rugose; propodus subrectangular ( Figs. 1A View Fig , 3C View Fig ). Male abdomen relatively broad; telson semicircular ( Fig. 3E View Fig ). G1 slender; distal chitinous part elongate; spatuliform, subtruncate tip with weak indentation ( Fig. 3 View Fig G–I).

Colour. In life, the specimens were brownish red, with pale yellow chelae.

Etymology. The species is named after the island where it was discovered. The specific epithet, bintan , is used as a noun in apposition.

Remarks. Geosesarma bintan , new species, belongs to the same species group as G. peraccae ( Nobili, 1903) in its carapace being distinctly broader than long, the presence of a flagellum on the exopod of the third maxilliped, the relatively broad meri of the ambulatory legs, and a G1 which is slender and its chitinous tip spatuliform ( Ng, 1988). It is perhaps closest to G. peraccae and G. penangense ( Tweedie, 1940) in the general form of its carapace and gonopods. The new species can be separated from G. peraccae (type locality: Singapore) by its relatively more slender third maxilliped meri ( Fig. 3A View Fig ) (distinctly broader in G. peraccae ; cf. Ng, 1988: fig. 56C), relatively longer ambulatory legs ( Figs. 1A View Fig , 3C View Fig ) (shorter in G. peraccae ; cf. Ng, 1988: fig. 56A; Serène, 1968: pl. 1 fig. 2), and relatively shorter G1, with the chitinised part proportionately much shorter ( Fig. 3 View Fig G–I) (proportionately longer with the chitinised part more elongate in G. peraccae ; cf. Ng, 1988: fig. 56D–F; Serène, 1968: fig. 3, 4). It can be separated from G. penangense (type locality: Penang) by its relatively more slender third maxilliped merus ( Fig. 3A View Fig ) (broader in G. penangense ; cf. Ng, 1988: fig. 58C) and relatively more slender G1, with the chitinised part subtruncate ( Fig. 3 View Fig G–I) (stouter, with the chitinised part gently tapering, in G. penangense ; cf. Ng, 1988: fig. 58D–F).

The holotype of G. bintan , a male, is already mature, with its gonopods fully developed and chitinised, although its chelae are not enlarged, suggesting it can reach larger sizes. The same is known of the allied G. peraccae from Singapore, where only very large males have enlarged and brightly coloured chelae ( Ng, 1988).