Chiromantes haematocheir (De Haan, 1833)

(Figs. 1A, 3A, 5A–C, 7A–D, 9A, 10A–I, 43A)

Grapsus (Pachysoma) haematocheir De Haan, 1833: 62, pl. 7 fig. 4.

Holometopus haematocheir – H. Milne Edwards, 1853: 188; Stimpson, 1858: 106 (part); Heller, 1865: 66; Stimpson, 1907: 137 (part); Takeda, 1975: 146; Soh, 1978: 9, 10, pl. 2e; Takeda, 1982: 219, fig. 650.

Sesarma haematocheir – Herklots, 1861: 17; De Man, 1887: 642; Bürger, 1893: 614, pl. 21 fig. 3; Ortmann, 1894: 717 (part); Yamaguchi & Baba, 1993: 473, fig. 180c; Fransen et al., 1997: 129.

Sesarma (Holometopus) haematocheir – Tesch, 1917: 156; Balss, 1922: 155; Urita, 1926: 19; Shen, 1932: 199, text-figs. 124, 125, pl. 9 fig. 2; Sakai, 1936: 234, pl. 64, fig. 3; Sakai, 1939: 681, pl. 77, fig. 3; Shen, 1940a: 97; Shen, 1940b: 237; Kamita, 1941: 214, text-fig. 118; Shen & Dai, 1964: 134, unnumbered fig.; Sakai, 1965: 202, pl. 97, fig. 1; Serène, 1968: 107; Kim, 1973: 486, text-fig. 216, pl. 45 fig. 166; Sakai, 1976: 655 (part), pl. 224 fig. 1; Matsuzawa, 1977: pl. 110 fig. 1; Dai et al., 1986: 487, text-fig. 274(1), pl. 68(6); Dai & Yang, 1991: 534, textfig. 274(1), pl. 68(6); Huang, 1994: 597; Muraoka, 1998: 53.

Chiromantes haematochir – Liu & Ng, 1999: 229, 230.

Chiromantes haematocheir – Miyake, 1983: 179, pl. 60-1; Minemizu, 2000: 297; Kobayashi, 2000: 122, fig. 2p; Ng et al., 2001: 41 [includes references for this species from Taiwan up to 2001]; Schubart et al., 2002: 30; Ho, 2003: 38; Kwok & Tang, 2005: 3, fig. 8; Schubart et al., 2006: 195; Takeda & Ueshima, 2006: 94; Oh et al., 2007: 9; Ng et al., 2008a: 220; Yang et al., 2008: 801; Naruse & Ng, 2008: figs. 1–4, 5b; Lee, 2008: 134; Naderloo & Schubart, 2009: 61, 67; Liu & Wang, 2010: 58; Komai & Ng, 2013: 4, figs. 1–3, 4a, b, 5b; Toyota & Seki, 2014: 188; Ng et al., 2017b: 103 [for other local references for Taiwan].

Holometopus serenei Soh, 1978: 13, fig. c, d, pl. 1b, e, pl. 2f; Lee, 1995: 3.

Chiromantes serenei – Kwok & Tang, 2005: 3, fig. 9.

Material examined. Lectotype: male (33.7 × 29.65 mm) (RMNH D160), Japan, coll. Ph. v. Siebold. Paralectotypes: 1 female (27.5 × 23.5 mm) (RMNH D 158), Japan, coll. Ph. F. von Siebold, 1823–1829; paralectotypes, 4 males (16.9–28.9 × 14.8 × 25.3 mm), 1 female (26.7 × 22.0 mm) (RMNH D 159), Japan, coll. Ph. F. von Siebold, 1823–1829 ; 1 male (29.6 × 25.3 mm) (MNHN B-12475), Japan, coll. Ph. F. von Siebold, 1823–1829. Others: JAPAN – 2 males (larger 31.7 × 27.4 mm) (ZRC 1964.9.8.12–13), coll. S. Miyake; 1 male (26.4 × 22.9 mm), 1 female (26.6 × 22.4 mm) (ZRC 1970.8.27.7), Sagami Bay, Kamakura, coll. T. Sakai, 1968 ; 7 females (smallest 18.5 × 15.6 mm, largest 28.3 × 24.5 mm) (ZRC 2002.0225), river mouth, Izaku River, Satsuma Peninsula, Kagoshima Prefecture, coll. H. Suzuki, 30 August 2000 ; 1 male, 1 female (ZRC 2017.1004), stream about 50 m before coastline, Kamenoko-jima, Sasebo, Kyushu, 33.125941°N 129.678348°E, coll. P.K.L. Ng, T. Naruse, M. Deki et al., 30 October 2017 . TAIWAN – 1 male (26.7 × 24.2 mm), 2 females (22.8 × 19.6 mm, 13.9 × 11.9 mm) (ZRC), Yan Liau, coll. J.-F. Huang, 16 October 1985 ; 5 males (35.6 × 31.2 mm, 29.1 × 25.4 mm, 25.4 × 22.9 mm, 17.7 × 15.6 mm, 15.6 × 13.7 mm), 1 female (23.4 × 20.0 mm) (ZRC), Lion Museum, Peikuan, Toucheng town area, northeastern Taiwan, coll. H.-C. Liu & P.K.L. Ng, 21 June 2002 ; 3 males (ZRC 2009.0153), coastal area behind Lion Mountain, Pei Kuan, Ilan County, coll. N.K. Ng & P.-H. Ho, 25 June 2000 ; 1 juvenile male (ZRC 2009.0669), among grass, supralittoral zone, Hsinchu wetlands, Hsinchu, northwest coast, coll. P.K.L. Ng, 6 June 2009; 1 male (ZRC 2002.0472), Hualien County, mouth of Meilun stream, Hualien city, eastern Taiwan, 23°58′54″N 121°36′37″E, coll. P.K.L. Ng & H.-C. Liu, 22 June 2002 . CHINA – 1 male (ZRC 2002.0558), Chao Pu-Tou mangroves, You Long village, mainland, outside Xiamen island, Xiamen, Fujian province, China, coll. P.K.L. Ng & S.H. Fang, 22 September 2002 . HONG KONG – 1 male (18.2 × 16.6 mm) (NHM 1978.107) (lectotype of Holometopus serenei Soh, 1978), Tai Po ricefield, coll. C.L. Soh, 8 June 1975 ; 1 male (35.3 × 30.6 mm) (ZRC), in aquarium, coll. H.H. Tan, July 2000; 7 females (largest 12.0 × 10.7 mm, smallest 24.5 × 21.1 mm) (ZRC 1997.761), salt marsh, Tai Tam, south coast of Hong Kong Island, immediately downstream of Tai Tam Dam, coll. P.K.L. Ng & S.Y. Lee, 6 June 1996 ; 1 male (30.8 × 26.9 mm) (ZRC), salt marsh, Tai Tam, south coast of Hong Kong Island, immediately downstream of Tai Tam Dam, coll. K. Wong, 3 October 2010 ; 15 males (smallest 9.8 × 11.2 mm, largest 27.8 × 23.9 mm), 6 females (smallest 11.1 × 9.5 mm, largest 21.1 × 18.4 mm) (ZRC 2012.1221), salt marsh, Tai Tam, south coast of Hong Kong Island, immediately downstream of Tai Tam Dam, coll. K. Wong, 27 March 2012 ; 4 males (10.2 × 8.7 mm, 10.8 × 9.4 mm, 11.6 × 9.6 mm, 14.3 × 13.0 mm), 1 female (17.5 × 15.1 mm) (ZRC 2012.1222), salt marsh, Tai Tam, south coast of Hong Kong Island, immediately downstream of Tai Tam Dam, coll. K. Wong, 17 September 2012 .

Diagnosis. Ambulatory legs relatively stouter, shorter, distal end of second ambulatory merus just reaches frontal margin when folded; row of granules on dorsal margin of cheliped dactylus only distinct in smaller specimens, very low or undiscernible in large males; male pleonal somite 6 is relatively narrower.

Colour. The carapace of adult C. haematocheir is usually dark green with the anterior parts and margins yellowish to red (see also Miyake, 1983; Minemizu, 2000; Lee, 2008: 134; Liu & Wang, 2010: 58; Toyota & Seki, 2014).

Remarks. There are 25 type specimens (and a set of dried mouthparts) of this species in RMNH (Fransen et al., 1997), with the lectotype designated by Yamaguchi & Baba (1993). The lectotype male is a specimen in excellent condition, despite its age.

Soh (1978) described Holometopus serenei from Hong Kong. Shen (1940a: 237) had earlier recorded C. haematocheir from Hong Kong from a site called Wong Chuk Hang, a small village near Aberdeen, but Soh (1978: 10) noted that he could not find the species there as the area had since been developed. Examination of the lectotype of Holometopus serenei Soh, 1978, as well as numerous specimens from various locations around Hong Kong, confirms that it is only a junior synonym of C. haematocheir . All specimens reported or here examined are only juveniles or subadults of C. haematocheir (see also Ng et al., 2008a; Naruse & Ng, 2008). The holotype male of H. serenei is not fully mature, as evidenced by its poorly developed chelae. The G1 of the type of H. serenei, however, is relatively well developed and is almost identical to that of C. haematocheir . The male pleon of H. serenei has the telson and somite 6 relatively more elongate than adult C. haematocheir, but this is also clearly associated with size and age. Medium-sized specimens of C. haematocheir from Japan have male pleons intermediate in form between the holotype of H. serenei and adult C. haematocheir . The paratype females of H. serenei are already mature despite being relatively small, but such early maturity is not abnormal—we similarly have a good series of small adult females of C. haematocheir from Taiwan and Japan. Direct comparisons of specimens of C. haematocheir comparable in size from Taiwan to the male holotype of H. serenei do not show any major differences.

The good series of specimens from Hong Kong has allowed us to estimate the size at which males and females of this species mature. Two small female specimens (11.1 × 9.5 mm, 14.1 × 11.8 mm) (ZRC 2012.1221) are not fully mature with the pleon not completely covering the thoracic sternum, although a slightly larger specimen (14.5 × 12.1 mm) from the same locality is already mature. The species therefore can mature at a relatively small size. The males also appear to be able to reach maturity at smaller sizes. As noted above, the small lectotype male of H. serenei (18.2 × 16.6 mm) is already mature, with the G1 fully developed. Surprisingly, an even smaller male (9.8 × 11.2 mm) (ZRC 2012.1222) is also mature. The structure of the male thoracic sternum also varies with size. Small specimens (10.8 × 9.4 mm) (ZRC 2012.1222) have a sternite 4 that is relatively wider, becoming gradually longer as they increase in size (Fig. 7A–D). Why some specimens from Hong Kong can mature at these smaller sizes is not known, some of the specimens we have from there are larger and agree with what we know from other parts of its range (e.g., in Japan and Taiwan). We are also uncertain if this phenomenon occurs in other parts of its range.

The lateral carapace margin of C. haematocheir is usually entire, especially in adults and males. In smaller female specimens, however, the margin has two very broad and low lobiform teeth separated by very short and very narrow fissures, which are just discernible under magnification.

Although most of the literature describes the dactylar finger of adult males of C. haematocheir as unarmed, this is actually not the case. As discussed at length by Naruse & Ng (2008), the dorsal margin of the dactylar finger is actually lined with a row of regularly shaped low subrectangular granules that are especially prominent in smaller specimens (Fig. 5C), becoming very low or undiscernible in large individuals (Fig. 5B). In fact, Holometopus serenei Soh, 1978, was partially diagnosed on this basis. Specimens of the closely related C. ryukyuanus of a comparable size to C. haematocheir have proportionately larger granules, that are distinct even in large specimens.

Although we do not have morphological support, our phylogenetic reconstruction (Fig. 59) does suggest the possibility that there could still be more than one species within Chiromantes haematocheir as defined here. If this is the case, it remains possible that C. serenei may still be recognised in the future as a valid cryptic or pseudocryptic species. A more detailed study with a larger series of samples (both morphological and molecular) across the known range of Chiromantes haematocheir will need to be undertaken before this problem can be resolved.

The record of “ Chiromantes haematocheir ” by Liu & He (2007: 162) from China is actually Parasesarma affine (De Haan, 1837) (cf. Rahayu & Ng, 2010).

Biology. This species is found in supralittoral habitats, usually some distance from the sea, often adjacent to or near freshwater habitats. They may be found several kilometres inland if the area is flat and still subjected to some tidal influence. The larval development has been reported by Fukuda & Baba (1976) and Oh et al. (2007). Nematode parasites have been reported on by Yoshimura (1990).

Distribution. Widely distributed in East Asia, from Korea to mainland Japan, Taiwan, and mainland China, including Hong Kong.