Pseudosesarma anteactum, Ng & Schubart, 2017

Ng, Peter K. L. & Schubart, Christoph D., 2017, On the taxonomy of Pseudosesarma edwardsii (De Man, 1887) and P. crassimanum (De Man, 1887) (Crustacea: Decapoda: Brachyura: Sesarmidae), with description of a new species from Sri Lanka, Raffles Bulletin of Zoology 65, pp. 655-669 : 664-667

Pseudosesarma anteactum , new species

(Figs. 14–17)

Sesarma edwardsii – Alcock, 1900: 416 (part) (not Sesarma edwardsii De Man, 1887 ).

Sesarma (Sesarma) edwardsi crassimana – Ingle & Fernando, 1963: 101, figs. 1, 2a, b (not Sesarma edwardsii var. crassimana De Man, 1887 ).

Pseudosesarma crassimanum – Bouillon et al., 2004: 84; Dahdouh-Guebas et al., 2011: 192 (not Sesarma edwardsii var. crassimana De Man, 1887 ).

Material examined. Holotype, male (16.7 × 14.7 mm) (ZRC 2016.0602), Colombo, Sri Lanka, coll. R. Serène, 12 October 1972. Paratypes: 3 males (21.2 × 19.7 mm, 17. 2 × 15.9 mm, 14.1 × 12.2 mm), 2 females (17.5 × 15.4 mm, 15.7 × 14.2 mm) ( ZRC 2016.0603), same data as holotype. Fig. 14. Pseudosesarma anteactum , new species. A–D, holotype male (16.7 × 14.7 mm) ( ZRC), Sri Lanka; E, paratype male (21.2 × 19.7 mm) ( ZRC), Sri Lanka. A, overall dorsal view; B, E, dorsal view of carapace; C, frontal view of cephalothorax; D, left third maxilliped. Fig. 15. Pseudosesarma anteactum , new species. A, B, holotype male (16.7 × 14.7 mm) ( ZRC 2016.602), Sri Lanka; C, D, paratype male (21.2 × 19.7 mm) ( ZRC 2016.603), Sri Lanka. A, C, anterior thoracic sternum and pleonal somites 4–6 and telson; B, D, outer view of right chela.

Diagnosis. Carapace transversely rectangular (Figs. 14A, B, E, 16A); frontal margin relatively wider, median concavity separating lobes distinct (Fig. 14A, B, E, 16A); epibranchial tooth distinct, separated from rest of margin by deep notch (Figs. 14B, E, 16A); posterolateral margins subparallel ( Figs. 2C , 8 ); outer surface of chela gently convex, covered with closely packed rounded granules, ventral margin of palm gently convex, lined with rounded granules, not denticulate, fingers relatively short compared to overall chela (Figs. 15B, D); suture between male thoracic sternites 3 and 4 distinct (Fig. 15A, C); male pleon broadly triangular (Fig. 15A, C); male sternopleonal cavity with press-button of pleonal locking mechanism on sternite 5; distal half of G1 gently swollen, wider than proximal part, median part appears gently constricted, chitinous part forming relatively wide beak-like structure (Fig. 17A–F). Colour of chelae in life not known.

Etymology. From the Latin “for the past”, alluding to the fact that the type material was collected by noted carcinologist Raoul Serène in the early 1970s, but still is of substantial systematic value to researchers over 40 years later.

Remarks. In the carapace shape, structure of the frontal margin, shape of the male pleon and proportions of the male chelae, P. anteactum , new species (Figs. 14A, B, E, 15A–D, 16A) closely resembles P. crassimanum ( Figs. 8–10 ). The chela of P. anteactum , however, has the ventral margin of the palm gently convex (Fig. 15B, D) rather than concave ( Fig. 9 ). Most significantly, the G1 structures are quite different. In P. anteactum , the median part of the G1 appears gently constricted with the proximal and subdistal parts dilated, and the distal chitinous part is relatively wider and more truncate (Fig. 17A–F). In P. crasssimanum , the subdistal part of the G1 is more dilated than the relatively more slender proximal parts, and the distal chitinous part is proportionately narrower, more acute and beak-like ( Fig. 11B–F, H–L, O–R ).

Figures

Fig. 2. A, Pseudosesarma edwardsii (De Man, 1887), lectotype male (17.5 × 16.1 mm) (NNM-D17a), Mergui Archipelago; B, Pseudosesarma edwardsii, male (21.3 × 18.7 mm) (ZRC 2003.84), Singapore; C, D, Pseudosesarma crassimanum (De Man, 1887), lectotype male (16.3 × 14.6 mm) (NHM 1886.52b), Myanmar. A, C, dorsal view of carapace; B, D, frontal view of cephalothorax.

Fig. 8. Pseudosesarma crassimanum (De Man, 1887), overall view. A, lectotype male (16.3 × 14.6 mm) (NHM 1886.52b), Myanmar; B, paralectotype male (18.8 × 16.7 mm) (NHM 1886.52c), Myanmar; C, male (15.9 × 14.3 mm) (ZRC 2008.442), Ranong; D, male (14.0 × 11.9 mm) (MNHG), Sarawak; E, male (15.9 × 14.5 mm) (NNM D23313), Singapore; F, male (18.9 × 16.7 mm) (ZRC 1998.851), Sarawak; G, male (17.2 × 15.0 mm) (ZRC 1999.503), Kalimantan; H, male (17.5 × 15.0 mm) (ZRC 1967.7.21.4), Singapore.

Fig. 9. Pseudosesarma crassimanum (De Man, 1887), chela. A, lectotype male (16.3 × 14.6 mm) (NHM 1886.52b), Myanmar; B, paralectotype male (18.8 × 16.7 mm) (NHM 1886.52c), Myanmar; C, male (15.9 × 14.3 mm) (ZRC 2008.442), Ranong; D, male (15.9 × 14.5 mm) (NNM-D23313), Singapore; E, H, male (17.5 × 15.0 mm) (ZRC 1967.7.21.4), Singapore; F, male (18.9 × 16.7 mm) (ZRC 1998.851), Sarawak; G, male (17.2 × 15.0 mm) (ZRC 1999.503), Kalimantan.

Fig. 11. Pseudosesarma crassimanum (De Man, 1887). A–G, lectotype male (16.3 × 14.6 mm) (NHM 1886.52b), Myanmar; H–M, male (15.9 × 14.3 mm) (ZRC 2008.442), Ranong; N–R, male (15.9 × 14.5 mm) (NNM-D23313), Singapore. A, N, pleon; B–F, right G1; G, right G2; H–L, O–R, left G1; M, left G2. Scales: A = 2.0 mm; B, G, H, I, M, O, P = 1.0 mm; N = 5.0 mm; C–F, J–L, Q, R = 0.5 mm.