Pseudosesarma edwardsii (De Man, 1887)

(Figs. 22A–C, 25A, B, 27A–C, 30A, B, 32 A, 34, 44 A, 56 A–E)

Sesarma edwardsii De Man, 1887: 649.

Sesarma edwardsi – De Man, 1888: 185, pl. 13 figs. 1–4; Lanchester, 1900: 757.

Sesarma (Sesarma) edwardsi – Tesch, 1917: 147 (part?).

? Sesarma (Sesarma) edwardsii – Calman, 1925: 166.

Sesarma (Sesarma) edwarsi (sic) – Serène, 1968: 105.

Pseudosesarma edwarsi (sic) – Serène & Soh, 1970: 399, 406.

Pseudosesarma edwardsii – Tan & Ng, 1994: 82; Fransen et al., 1997: 127; Ng et al., 2008a: 222; Ng & Schubart, 2017: 655, figs. 1A–C, 2A, B, 3–7, 12.

Not Sesarma edwardsi Ortmann, 1894: 721 = Bresedium brevipes (De Man, 1889).

Material examined. Lectotype (here designated): male (17.5 × 16.1 mm) (RMNH-D17 a), Mergui Archipelago, Myanmar, coll. J. Anderson, 1886. Paralectotypes: 1 female (RMNH-D17 b), same data as lectotype; 1 young male (7.9 × 7.0 mm), 8 females (20.3 × 17.7 mm, 14.9 × 13.2 mm, 13.8 × 12.7 mm, 13.7 × 12.5 mm, 12.3 × 11.6 mm, 12.3 × 11.3 mm, 10.9 × 10.2 mm, 8.8 × 7.9 mm) (NHM 1886.52 a), same data as lectotype. Others: SINGAPORE – 1 male (19.4 × 17.3 mm) (ZRC 1971.9.24.8), Sungei Seletar, coll. C.L. Soh, 29 March 1966; 1 male (ZRC 1965.7.29.50), Pulau Aya, Merban, coll. F.N. Chasen, 1931; 1 male (ZRC 1971.9.24.9), Sungei Seletar, coll. C.L. Soh, 29 March 1966; 1 male (ZRC 2003.0083), Pulau Ubin, vicinity of Asam mangroves (pitfall trap), coll. R. Teo, 20 September 2001; 1 male, 1 female (ZRC 2000.2019), Pulau Ubin, coll. C.D. Schubart, July 2000; 3 males (ZRC), swamp along dirt road to Chek Jawa, Pulau Ubin, coll. C.D. Schubart, 25 November 2011; 1 male (ZRC 2003.0084), culvert beside reservoir, Pulau Tekong, Singapore, coll. B.Y. Lee, 16 November 2001; 1 female (11.5 × 10.0 mm) (ZRC 2013.1116), near stream, northern axis of Pulau Tekong, coll. T.M. Leong, 31 January 2002; 1 ex-ovigerous female (19.1 × 17.8 mm, first zoeae reared and preserved) (ZRC), in secondary forest, 300 m from coast, coll. M. Chua, 24 March 2012. PENINSULAR MALAYSIA – 1 male (ZRC 1984.8031), Pangkor Island, Straits of Malacca, coll. 13 August 1967; 1 male, 1 female (ZRC 2010.0035), Pulau Langkawi, Temurun waterfall, coll. P.K.L. Ng, 17 June 1998; 1 male (13.9 × 12.9 mm), 1 female (13.1 × 11.6 mm) (ZRC), Sungei Temurun Datai, Langkawi, Kedah, Malaysia, coll. Universiti Sains Malaysia, 1 April 2003; 1 male (19.4 × 18.2 mm), 1 female (19.3 × 17.7 mm) (NHMW 26842), Pulau Langkawi, Air Temurun waterfall and stream, coll. C.D. Schubart et al., 15 March 2006; 8 males (1 post-molt, badly damaged), 3 females (ZRC 2016.0608), Temurun waterfall, at base of waterfalls, under rocks at side of stream, near bank, about 200 m from sea, Langkawi, Peninsular Malaysia, coll. P.K.L. Ng & P.Y.C. Ng, 18 December 2016.

Diagnosis. Carapace transversely rectangular; frontal margin less wide, median concavity separating lobes relatively more shallow; epibranchial tooth distinct, separated from rest of margin by deep notch; posterolateral margins subparallel; outer surface of chela gently convex, covered with small rounded granules, ventral margin of palm sinuous, unarmed; suture between male thoracic sternites 3 and 4 distinct; male pleon broadly triangular; male sternopleonal cavity with press-button of pleonal locking mechanism on sternite 5; distal part of G1 bifurcated or bilobed, with chitinous part very short. In life, chelae red, pigmentation extending to midway of white fingers.

Colour. The carapace of fresh P. edwardsii is brown to reddish-brown, with many specimens having the posterior part of the carapace slightly to much darker in colour (Fig. 56A, C), with the outer surface of the chela red, the colour extending to at least the middle of both fingers, with the distal half white (Fig. 56B, D, E) (see also Ng & Schubart, 2017).

Remarks. The taxonomy of this species has been discussed at length by Ng & Schubart (2017) and there is no need to further elaborate. The date of publication for this species (and P. crassimanum) follows Ng et al. (2015). Ng & Schubart (2017) clarified the differences with P. crassimanum (De Man, 1887) and further realised that P. edwardsii s. lat. was harbouring a number of closely related species, including P. anteactum Ng & Schubart, 2017, from Sri Lanka, P. glabrum Ng, Rani & Nandan, 2017, from western India, and P. brehieri Ng, 2018, from Myanmar.

Ng & Schubart (2017) observed that the proportions of the male pleon varies with size. In the largest male, the lectotype, from the Mergui (17.5 × 16.1 mm, RMNH-D17), the pleon is very wide (Figs. 30A, 34B) but it is narrower in smaller males (Figs. 30B, 34C). Larger males also have proportionately stouter G1s, with the distal part distinctly bilobed (Fig. 34D, E) while those of smaller males are more slender with the distal part less obviously bilobed.

The identity of “ Sesarma (Sesarma) edwardsii ” from Pasir Ganing in western Sumatra by Calman (1925: 166) cannot be confirmed. It is within the range of variation of the present species, so it is here retained within its synoymy. The specimens should be re-examined when possible.

Specimens reported as “ S e s a r m a e d w a r d s i ” and “ Pseudosesarma edwardsii ” from many parts of Burma, India, Andamans, Bangladesh, Sri Lanka by Alcock (1900: 416), Mandal & Nandi (1989: 25), Kathirasan (2000: 193), Dev Roy & Nandi (2001: 18), Dev Roy & Bhadra (2007: 143, pl. 4 fig. 5), Dev Roy (2008: 131), Paul et al. (2012: 193), Holmes et al. (2014: 160) and Shet et al. (2016: 8, 12, fig. 2) (see Trivedi et al., 2018: 73); as well as Java, Sulawesi, and New Guinea by Tesch (1917: 147) probably belong to other species. The material from Sri Lanka by Alcock (1900) was referred to P. anteactum; while specimens from Kerala in West India probably belong to P. glabrum; as does most western Indian material. Specimens from northeastern India belong to P. brehieri and we have some specimens from West Bengal that confirm this (Fig. 37F–I). The precise identities of all these records can only be determined after re-examining the specimens. Ortmann’s (1894: 721) record of “ Sesarma edwardsi ” from Australia is probably Bresedium brevipes (De Man, 1889) (see also Laurie, 1906; McNeill, 1968; Davie, 2002).

Biology. Pseudosesarma edwardsii is typically found in well-forested coastal freshwater or brackish water habitats. They are semiterrestrial and live on the banks of streams as well as swamps, and are often found under rocks and vegetation. They are sometimes found several hundred metres from the sea, even at the base of waterfalls. They have small eggs and it is clear their larval development remains tied to the open sea.

Distribution. Mergui Archipelago and Andamans to Peninsular Malaysia and Singapore, possibly to Java and Sulawesi (De Man, 1887; Tesch, 1917; Ng & Schubart, 2017).