Orisarma sinense (H. Milne Edwards, 1853)

(Figs. 2G–J, 3E, 6E–H, 8D, 9F, G, 12F–J, 54D)

Sesarma sinensis H. Milne Edwards, 1853: 186; Stimpson, 1858: 105; De Man, 1887: 648, 669; Stimpson, 1907: 133; Wang & Leung, 2001: 31, unnumbered figure.

Sesarma (Sesarma) sinensis – Tesch, 1917: 199; Shen, 1931: 196, text-fig. 13, pl. 14 figs. 2, 3; Shen, 1940a: 96; Serène, 1968: 105.

Sesarma (Sesarma) intermedia – Balss, 1922: 155 (part). [not Grapsus (Pachysoma) intermedius De Haan, 1835]

Sesarmops sinensis – Serène & Soh, 1970: 401; Soh, 1978: 11, pl. 4c; Kwok & Tang, 2005: 3, figs. 15, 18a, 20; Yang et al., 2008: 802; Huang et al., 2011: 732, 733; Tang et al., 2017: e0179800.

Sesarma (Sesarmops) sinensis – Dai et al., 1986: 492, text-fig. 277(2), pl. 69(6); Dai & Yang, 1991: 539, text-fig. 277(2), pl. 69(6); Huang, 1994: 597.

“ Sesarmops ” sinensis – Ng et al., 2008a: 220.

Sesarmops intermedium – Sulieman & Pengsakul, 2013: 1. [not Grapsus (Pachysoma) intermedius De Haan, 1835]

Material examined. Lectotype male (19.0 × 16.6 mm) (MNHN-BP3635 a), China . Paralectotype: 1 female (18.8 × 16.9 mm) (MNHN-BP3635 b), same data as lectotype. CHINA – 5 males (largest 30.0 × 25.9 mm, smallest 28.6 × 25.5 mm), 1 female (ZRC 1998.1204), Shanghai, Qidong, Jiangsu Province, coll. Y.Y. Li, 2 May 1996 ; 4 females (smallest 22.9 × 20.3 mm, largest 31.8 × 26.6 mm) (ZRC), Qi Dong, Lusi, Shanghai, coll. Y.Y. Li, 1 May 1996 ; 1 male (30.7 × 26.7 mm), 1 female (ZRC 2010.0421), southern Chongming, 31°30.135′N 12°42′E, coll. H. Cao, 15 July 2010 . HONG KONG – 1 female (22.0 × 18.5 mm) (ZRC 1975.6.30.10), Shiu Hau, Lantau Island, coll. C.L. Soh, 2 June 1975 .

Diagnosis. Dorsal surface of carapace relatively more convex, surfaces usually slightly smoother, with very few stiff setae on anterior and branchial regions; frontal lobes separated by relatively more shallow concavity; epibranchial tooth relatively low, almost confluent with rest of margin in small specimens, separated from rest of lateral margin by gentle notch; posterolateral margins subparallel; granules on outer surface of palm (especially those below longitudinal ridge) relatively lower, more flattened; merus of ambulatory legs relatively shorter; chitinous distal part of G1 long, tip truncate. In life, carapace and chelae red.

Colour. In life, the species is pale to bright red overall (Fig. 54D).

Remarks. The identity of this species from somewhere in China has been hampered by the fact that H. Milne Edwards (1853: 186) described the species very briefly, without any figures and no indication of size, sex, or number of specimens used. Even when the types were apparently re-examined (e.g., De Man, 1887: 648), no figures were provided. The type specimens consist of two small, dried specimens in poor condition (Fig. 2G, H). However, they clearly show the key characters for the species, including the diagnostic G1 structure (Fig. 9F). Both specimens are syntypes and the male is here designated the lectotype of Sesarma sinensis H. Milne Edwards, 1853 .

The key differences between O. sinense and O. intermedium have been discussed under the latter species.

The small female from Hong Kong (ZRC 1975.6.30.10) examined here is probably the same specimen figured by Soh (1978: pl. 4c) and agrees with S. sinense as presently defined.

Biology. The biology of O. sinense, is probably similar to O. intermedium but little is known. Sulieman & Pengsakul (2013) recorded “ Sesarmops intermedium ” as a potential biological control for pomatiopsid snails in Jiangxi Province, China, but based on the distribution, their species is almost certainly O. sinense instead. Specimens of this species from Shanghai were observed climbing several metres up trees at night foraging for food (W. Liu, pers. comm., Fig. 54D). This is a behaviour that has been observed in other sesarmids from Southeast Asia (notably Episesarma De Man, 1895) (see Sivasothi, 2000; Sivasothi et al., 1993; Ng et al., 2008b). Tang et al. (2017) obtained the complete mitochondrial genome of the species from China.

Distribution. See comments for O. intermedium .