Orisarma dehaani (H. Milne Edwards, 1853)

(Figs. 1C, D, 3B, 4A, B, D, F, 5D–F, 7E–G, 9C, 11A–G, 43B, 53A–E)

Grapsus (Pachysoma) quadratus – De Haan, 1835: 62, pl. 8 fig. 3.

Sesarma dehaani H. Milne Edwards, 1853: 184; Stimpson, 1858: 106 (part); De Man, 1887: 642; Bürger, 1893: 615; Ortmann, 1894: 718; Stimpson, 1907: 134 (part); Yamaguchi & Baba, 1993: 478, fig. 18b; Fransen et al., 1997: 128; Wang & Leung, 2001: 31, unnumbered figure.

Sesarma hanseni Rathbun, 1897: 92; Abele, 1975: 48, figs. 1, 2.

Sesarma (Holometopus) dehaani – Tesch, 1917: 158; Balss, 1922: 154 (part); Sakai, 1936: 234, pl. 65, fig. 1; Sakai, 1939: 682, pl. 77, fig. 1; Shen, 1940a: 97; Kamita, 1941: 217, text-fig. 120; Sakai, 1965: 202, pl. 97, fig. 2; Serène, 1968: 107; Baba & Miyata, 1971: 54; Kim, 1973: 487, text-fig. 217, pl. 95 fig. 167a, b, pl. 96 fig. 167c, d; Sakai, 1976: 655, pl. 224 fig. 2; Matsuzawa, 1977: pl. 110 fig. 2; Dai et al., 1986: 488, text-fig. 274(2), pl. 68(7); Nagai & Nomura, 1988: 43; Dai & Yang, 1991: 534, text-fig. 274(2), pl. 68(7); Huang, 1994: 597; Muraoka, 1998: 53.

Holometopus dehaani – Takeda, 1975: 147; Soh, 1978: 9, 10, pl. 2d; Takeda, 1982: 220, fig. 651.

Chiromantes dehaani – Miyake, 1983: 179, pl. 60-2; Liu & Ng, 1999: 229; Minemizu, 2000: 298; Kobayashi, 2000: 122, fig. 2n; Ng et al., 2001: 41 [includes references for this species from Taiwan up to 2001]; Kwok & Tang, 2005: 3, fig. 7; Takeda & Ueshima, 2006: 93; Lee, 2008: 135; Yang et al., 2008: 801; Naderloo & Schubart, 2009: 61–63, 67; Hong et al., 2010: 259; Liu & Wang, 2010: 57; Huang et al., 2011: 732; Li & Chiu, 2013: 40; Komai & Ng, 2013: 540, figs. 1B, 6A, 7A–C, G; Toyota & Seki, 2014: 190; Ng et al., 2017b: 102 [for other local references for Taiwan].

“ Chiromantes ” dehaani – Ng et al., 2008a: 220.

Material examined. Lectotype male (39.5 × 35.7 mm) (RMNH D 157), Japan, coll. v. Siebold. Others: JAPAN – 1 male (35.0 × 38.5 mm) (CBM-ZC 165), Obitsu River estuary, Kisarazu, Chiba Prefecture, July 1990, coll. T. Furota; 1 male (31.0 × 28.3 mm) (CBM-ZC 169), Hanami River, Chiba, Chiba Prefecture, coll. Nakano, 5 October 1990; 1 male (28.3 × 25.4 mm) (CBM-ZC 11406), Yahata Channel, Ichihara, Chiba Prefecture, coll. J. Takayama, 30 August 2012; 6 males (23.9 × 22.0 mm to 42.0 × 37.7 mm), 3 females (23.9 × 22.0 mm to 29.5 × 26.9 mm) (CBM-ZC 11458), Kaneda, Kisarazu, coll. T. Komai, May 2009; 1 male (27.3 × 24.5 mm) (ZRC 1968.4.22.12), coll. T. Sakai, 1968; 1 female (24.3 × 21.5 mm) (ZRC 1970.8.27.1), Kamakura, Kanagawa Prefecture, Sagami Bay, coll. T. Sakai, 1968; 2 males (22.0 × 20.2 mm, 23.5 × 21.1 mm) (CBM-ZC 7576), Tatara River, Fukuoka, Fukuoka Prefecture, coll. Y. Matsuzawa, March 2003; 1 ovigerous female (21.4 × 19.4 mm) (ZRC 2002.0226), river mouth, Izaku River, Satsuma Peninsula, Kagoshima Prefecture, coll. H. Suzuki, 30 August 2000; 2 males (larger 23.4 × 20.8 mm), 2 females (larger 25.2 × 22.0 mm) (ZRC 2012.0057), Koutsuki River, Kagoshima City, coll. P.K.L. Ng et al., 24 October 2011; 1 male (25.6 × 23.0 mm), 1 ovigerous female (27.4 × 23.9 mm) (CBM-ZC 3129), Tomari, Kume Island, Ryukyu Islands, coll. T. Komai, 12 June 1995; 1 male (38.3 × 36.6 mm) (ZRC 2011.1026), Zenda Forest Park, Kume Island, Ryukyu Islands, coll. T. Naruse et al., 15 November 2009; 3 males (largest 38.4 × 35.5 mm), 1 female (26.6 × 23.7 mm) (ZRC 2011.1027), Zenda Forest Park, Kume Island, Ryukyu Islands, coll. P.K.L. Ng et al., 17 November 2006; 1 female (36.2 × 31.7 mm) (CBM-ZC 9870), Ohtomi, Iriomote Island, Yaeyama Islands, coll. N. Shikatani, 29 April 1998; 1 male (35.4 × 32.4 mm) (ZRC 2000.2263), Iriomote Island, Ryukyu Islands, coll. Y. Cai & N.K. Ng, 15 June 2000. TAIWAN – 1 male (28.3 × 25.7 mm) (ZRC 2001.0025), near Tashi, northern Taiwan, coll. K.-X. Lee, 2000; 1 male (26.2 × 23.9 mm) (ZRC 2009.0871), Meilun stream, Hualien, coll. H.-C. Liu, 27 January 2002; 1 male, 1 female (ZRC 2000.1847), Hsinfeng mangroves, Hsinchu, coll. H.-C. Liu & C.D. Schubart, 17 September 1999; 1 male (ZRC 2002.0414), Lion Museum, Peikuan, Toucheng town area, coll. H.-C. Liu, 21 June 2002. CHINA – 2 males (ZRC 2010.0326), purchased, aquarium trade, supposedly from Guangzhou, China, coll. P.K.L. Ng, 2010. HONG KONG – 2 males (29.6 × 27.6 mm, 30.0 × 26.8 mm) (ZRC 2002.0223), coll. H.H. Tan, July 2000; 2 males (24.7 × 21.5 mm, 22.5 × 19.5 mm), 1 female (24.8 × 21.2 mm) (ZRC 1975.6.30.12–14), Tai Po, New Territories, coll. C.L. Soh, 8 June 1975; 6 males, 2 females (ZRC 2019.0539), back mangroves, ca. 22.492306°N 114.036169°E, Mai Po Nature Reserve, coll. S. Cannici, K. Wong, et al. 24 May 2019.

Diagnosis. Carapace distinctly quadrate to transversely rectangular; lateral margin crenulated to entire but no trace of epibranchial tooth; posterolateral margins subparallel or gently converging towards posterior carapace margin; dorsal surface relatively lower, gastric region less swollen, grooves separating regions deep, prominent; frontal lobes separated by deep, broad concavity; ambulatory merus relatively broader; chitinous part of G1 with basal part slightly constricted, distal part relatively broader. In life, carapace dark grey to brown, often with dark median patches, chelae grey to white, with proximal parts sometimes purplish.

Colour. The dorsal carapace surface of fresh O. dehaani is grey to dark purplish-brown, often with black or dark blotches on the gastric and adjacent areas (Fig. 53A, C). The chelipeds vary from white to pale purple (see also Miyake, 1983; Minemizu, 2000; Liu & Wang, 2010; Li & Chiu, 2013; Toyota & Seki, 2014).

Remarks. The type series is represented by 11 specimens (Fransen et al., 1997), and the lectotype was selected by Yamaguchi & Baba (1993). This well-known species has a wide range from Japan to southern China. The distribution is interesting as it seems to bracket the range of O. neglectum from Shanghai and Taiwan. The present specimens from Hong Kong are all easily referrable to O. dehaani as presently defined, confirming the reports of Soh (1978).

The record of S. hanseni Rathbun, 1897, from the West Indies is clearly incorrect (Abele, 1975: 48, figs. 1, 2), and from her description, it seems clear that this species is conspecific with S. dehaani .

Biology. Orisarma dehaani is typically associated with coastal rocky supralittoral habitats, living under rocks, or more often in deep burrows in the soil. They may be present in habitats over 100 metres from the shore or along coastal streams. This contrasts with the closely related O. neglectum that appears to prefer muddier and more open littoral habitats. Nara et al. (2006) discussed the social behaviour in this species in Japan, with Hong et al. (2010) commenting on its ecology from Korea. The larval development has been described by Baba & Miyata (1971). Nematode parasites have been reported on by Yoshimura (1990).

Distribution. Korea to Japan, Ryukyus, Taiwan, southern part of mainland China.