Contusarma cheirogonum (Targioni Tozzetti, 1877)

(Figs. 23D, G, H, 25I, 28 D, 31 B, C, 32 C, 39, 44 H, 57 B–H)

Sesarma cheirogona Targioni Tozzetti, 1877: 141–145, pl. 9, fig. 2a–g.

Sesarma bocourti – De Man, 1880: 28; Miers, 1880: 313; Zehntner, 1894: 182; Tweedie, 1940: 90.

Sesarma (Sesarma) bocourti – Nobili, 1900: 507; Tesch, 1917: 135, figs. 1, 2a; Balss, 1922: 155; Roux, 1933: 13.

Sesarma (Episesarma) bocourti – De Man, 1895: 169.

Pseudosesarma bocourti – Tan & Ng, 1994: 82; Ng, 1995: 200, fig. 14; Ng et al., 2008a: 222; Rademacher & Mengedoht, 2011: 30; Lim & Chua, 2015: 18; Ribero et al., 2020: 3.

Material examined. Neotype (here designated): male (24.5 × 21.5 mm) (ZRC 1995.225), peat swamp beginning of Ulu Assam trail, Bako National Park, Sarawak, Malaysia. coll. P.K.L. Ng & M. Lateef, 29 June 1994. SARAWAK – 3 males, 1 female (ZRC 1964.9.28.126–130), Stambak, Saribas, Sarawak, coll. L.K. Charles, 1950; 6 males, 2 females (ZRC 1964.9.28.131–139), Stambak, Saribas, coll. L.K. Charles, 1950; 1 male (26.3 × 23.0 mm) (ZRC 1995.226), peat swamp, beginning of Ulu Assam trail, Bako National Park, coll. P.K.L. Ng, 28 June 1994; 2 females (ZRC 2010.0063), Bako National Park trail, coll. rangers, May 2002. PENINSULAR MALAYSIA – 1 male (ZRC 1971.9.22.11), Kota Tinggi, Johor, Malaysia, coll. M.W.F. Tweedie, 1940; 5 males, 3 females (ZRC 1964.9.28.140–149), Kota Tinggi, Johor, coll. M.W.F. Tweedie, 1950; 16 males, 18 females (ZRC 1964.9.28.150–183), Kota Tinggi, Johor, coll. M.W.F. Tweedie, 1950; 4 males, 3 females (ZRC 1996.1724), Pulau Tioman, Sungei Ayer Besar, stream along beginning of Tekok Juara trail (Tekek side), coll. P.K.L. Ng et al., 29 June 1996; 1 male (ZRC 1999.890), Pulau Tioman, Juara tributary of Sungei Keliling, ca 500 m south after Sungei Keliling, coll. H.H. Tan, 18 June 1999; 3 males (ZRC 1999.611), Pulau Tioman, coll. P.K.L. Ng, 1996; 1 male (ZRC 1996.1726), Pulau Tioman, Kampung Genting, Sungei Ayer Raja, 2°45′36.7″N 104°07′21″E, coll. P.K.L. Ng et al., 15 September 1995; 3 females, 2 males (ZRC 2011.0924), stream from Tekek Bay, Pulau Tioman, coll. P.K.L. Ng, 23 June 1983; 7 males, 7 females (ZRC 1996.1725), Pulau Tioman, Sungei Keliling, coll. P.K.L. Ng, 27–28 June 1996; 1 male (ZRC 1998.850), Pulau Tioman, Sungei Keliling, coll. P.K.L. Ng et al., 26 June 1997; 1 male (ZRC 1998.851), Malaysia, Sungei Paya, Pulau Tioman, coll. P.K.L. Ng et al., 25 June 1997; 2 males, 1 female (ZRC 2019.1115), Sungei Paya, Tioman, Malaysia, coll. R. Diesel, 1995. SINGAPORE – 1 male (ZRC 1967.7.10.29), Sungei Seletar, coll. C.L. Soh, 15 January 1967; 1 female (ZRC 1967.7.10.33), Sungei Seletar, coll. C.L. Soh, 18 April 1968; 1 male (ZRC 1967.7.10.32), Sungei Seletar, coll. C.L. Soh, 31 December 1966; 1 male (ZRC 1967.7.10.28), Sungei China, coll. C.L. Soh, 15 January 1967; 1 male (ZRC 1967.7.10.30), Sungei Seletar, coll. C.L. Soh, 31 December 1966; 1 female (ZRC 1967.7.10.31), Sungei Seletar, coll. C.L. Soh, 21 March 1966; 1 male (ZRC 1973.11.2.492), Sungei Seletar, coll. C.L. Soh, 6 May 1966; 1 male (ZRC 2000.2018), Singapore, Pulau Ubin, caught dead, coll. C.D. Schubart, July 2000; 1 young female (ZRC), freshwater swamp, Belang, Pulau Tekong, Singapore, coll. K.K.P. Lim, 17 November 2012.

Diagnosis. Anterior dorsal carapace regions with scattered short black setae to almost glabrous; outer surface of adult chela covered with relatively smaller flattened granules, those on margins especially smaller, sharper; margins of ambulatory segments with scattered short setae; male pleon relatively transversely broader; G1 relatively more slender, chitinous distal part almost straight, proportionately more narrow.

Colour. In life, the carapace is dark purplish-black, with the posterior part sometimes lighter grey; lateral margins yellow to orange; outer surface of chela purple with orange to almost red fingers (Fig. 57B–H) (see also Rademacher & Mengedoht, 2011: 30).

Remarks. Targioni-Tozzetti (1877: 141) used the name “ Sesarma cheirogona ” for the species without any explanation of the etymology. The name is derived from the Greek Χειρός (cheira) for hand, and γωνία (gonía) for angle or joint; clearly alluding to the distinctive chela of the species. Targioni- Tozzetti (1877) probably did not intend to use the name as a noun as it should then have been spelled “ cheirogonia ”. Like most workers during that time, the gender of the name Sesarma was regarded as a feminine, and as such, he probably used “ cheiragona ” to reflect this.

For differences with C. bocourti, see Remarks for that species.

Biology. Ng (1995: 202) summarises the following observations about its ecology (as Pseudosesarma bocourti): “In the ZRC is a large series of this species from freshwater swamps in Kota Tinggi, Johor which had been collected by the late Michael Tweedie. I have also obtained specimens from coastal peat swamps in Pekan (Pahang) and Sarawak. The present specimens agree very well with these specimens. They dig burrows in the peat substrate, often among roots and debris, and emerge only late at night to feed on dead leaves and other vegetable matter. The crabs are terrestrial in habits and have been obtained several hundred metres from the nearest water source. The habitat (a coastal peat swamp) where they were collected, the beginning of the Ulu Assam trail, is only about 300 metres from the sea”.

Distribution. Sumatra, Borneo, Peninsular Malaysia, and Singapore.