Shinobium trapezoideum (H. Milne Edwards, 1837), comb. nov.

(Figures 8–11)

Sesarma trapezoidea H. Milne Edwards, 1834 –1840 (1837), p. 74 [type locality: not known]; 1853, p. 186; De Man 1887, p, 654, 678; 1889, p. 426, pl. 9, fig. 7; 1890, p. 96; 1892, p. 338; Ortmann 1894b, p. 719; Nobili 1900, p. 510; Schenkel 1902, p. 545; Estampador 1937, p. 537 [list]; Marquet 1991, p. 133.

Sesarma trapezoides: Weber 1892, p. 536 .

Sesarma oblonga Von Martens, 1868, p. 611 [type locality: Samar, Philippines].

Sesarma trapezoideum var. longitarsis De Man, 1889, p. 427, pl. 10, fig. 8 [type locality: Viti Islands].

Sesarma (Sesarma) trapezoideum: Rathbun 1907, p. 33; Serène 1968b, p. 106 (list).

Sesarma (Sesarma) trapezoidea: Nobili 1900, p. 510; 1907, p. 405; De Man 1902, p. 532. Roux 1917, p. 619; Tesch 1917, p. 207, 231 (list), 250 (key); Edmondson 1951, p. 237, fig. 33b; Forest and Guinot 1961, p. 157, figs 164–165.

Sesarma trapezoideum: Holthuis 1978, 27.

Labuanium trapezoideum: Serène and Soh 1970, p. 401; Poupin 1996, p. 70; Cai and Ng 2001, p. 691, fig. 18D–H; Davie 2002, p. 222; Keith et al. 2002, p. 26 (list), 32 (key), 66; Jeng et al. 2003, p. 228, figs 1–6; Cuesta et al. 2006, p. 156, fig. 5; Ng et al. 2008a, p. 221; Li and Chiu 2013, p. 24 (key), 45; Maenosono and Naruse 2016, p. 13, figs 6, 7; Maenosono 2017b, p. 351; Murata 2017, p. 11, fig. 1; Ng et al. 2017, p. 104, fig. 11c.

Sesarma (Labuanium) trapezoideum: McLay and Ryan 1990, p. 111 (list).

Material examined

Lectotype. MNHN-B3637, male, 30.0 × 29.0 mm, locality unknown.

Holotype of Sesarma trapezoideum longitarsis De Man 1889 . SMF 1980, 1 male, 31.4 × 28.9 mm, Viti Island, Fiji.

Others. ZRC 2018.0052, 1 male, 15.6 × 15.0 mm, Grotte Kafae, Funafus, Santo, Sanma, Vanuatu (SK 06-20-01; 167.0143333 − 15.537, alt. = 250 m), cave, Main river, on flood débris, by hand, coll. C. Rahmadi, 20 September 2006; ZRC 2018.0051, Vanuatu, 1 male, 29.5 × 26.8 mm, Patunar, Vanuatu, coll. L. Deharveng, 7 August 2006; ZRC 2008.0872, 1 male, 24.9 × 23.6 mm, 6 ovig. females, 18.8 × 17.8–25.8 × 23.9 mm, Murex Resort, Manado, N. Sulawesi, Indonesia, coll. P.K.L. Ng, H.H. Tan et al., July 2003; RUMF-ZC-5412, 1 female, 22.5 × 21.4 mm, same data as ZRC 2008.0872; ZRC 2002.0419, 1 male, 30.9 × 28.5 mm, 3 females, 28.7 × 26.0–30.9 × 35.8 mm, Changbin, Taitung County, E. Taiwan, 23.30611°N 121.4039°E, on moist rock face, at night, coll. P.K.L. Ng and H.-C. Liu, 22 June 2002; ZRC 2009.0320, 2 females, 32.9 × 29.6 mm (24 February 2000), 32.4 × 29.0 mm (3 March 2000), Andaman Islands, coll. I. Das; ZRC 2016.0020, 1 male, 35.4 × 32.4 mm, 1 female, 34.6 × 31.8 mm, Sungai Ifis, Halmahera, Indonesia, coll. D. Robb, Sep. 1994; RUMF-ZC -2962, 5 males, 7.1 × 6.7–9.4 × 8.9 mm, 6 females, 7.6 × 7.1–10.2 × 9.8 mm, Todoroki River, Ishigaki Island, southern Ryukyu Islands, Japan, coll. T. Maenosono, 17 May 2014; RUMF-ZC -2956, 1 male, 19.3 × 18.8 mm, Todoroki River, Ishigaki Island, southern Ryukyu Islands, Japan, coll. T. Maenosono, 22 March 2015; RUMF-ZC-2961, 1 female, 6.9 × 6.5 mm, Todoroki River, Ishigaki Island, southern Ryukyu Islands, Japan, coll. T. Maenosono and T. Naruse, 20 April 2015; RUMF-ZC-2960, 1 male, 24.0 × 22.5 mm, Todoroki River, Ishigaki Island, southern Ryukyu Islands, Japan, coll. T. Maenosono and R. Yoshida, 22 April 2015 . Colouration

In life, carapace dorsal surface black in general, mottled with whitish patches, suborbital region with a longitudinal yellow band below cornea. Mxp3 ischium whitish, merus dark except for proximal yellowish part. Pereopods also with black ground colour; cheliped merus and movable finger with a subproximal yellow band each, lower half of palm to proximal part of fingers around occlusal margin purple; ambulatory legs with a marked yellow band on middle of propodus and dactylus each. See Jeng et al. (2003, figs 2, 3); Maenosono and Naruse (2016, p. 16, fig. 6); Murata (2017, fig. 1); and Ng et al. (2017, fig. 11c).

Distribution

Eastern Indian Ocean to Central Pacific: Andaman Islands (Jeng et al. 2003), western Sumatra; eastern Indonesia (Sulawesi, Halmahera and Ambon) (De Man 1890, 1892; Nobili 1900; Schenkel 1902; Tesch 1917); the Philippines (Von Martens 1868; De Man 1887); Taiwan (Jeng et al. 2003); Ishigaki and Iriomote islands, southern Ryukyu Islands, Japan (Maenosono 2017b); northern Queensland, Australia (Ortmann 1894b); New Guinea (Roux 1917); Vanuatu (present study); Fiji (De Man 1889); Tahiti (Rathbun 1907), French Polynesia (Marquet 1991). Davie (2002) noted that this species is present in Micronesia and Hawaii, but no other references support these records.

Remarks

Von Martens (1868) described Sesarma oblonga from Samar, Philippines, without detailed comparisons with Sesarma trapezoideum . Later, De Man (1887, p. 679) compared the syntypes of Se. oblonga and Se. trapezoideum and found that the carapace was slightly longer than wide in the type of Se. oblonga, while it was slightly wider than long in the type of Se. trapezoideum, but considered that the difference should be attributed to individual or local variation. All the specimens of Shinobium trapezoideum examined in this study, including the lectotype of Se. trapezoideum and holotype of Se. trapezoideum longitarsis, have the carapace longer than wide. Von Martens (1868) measured the carapace of the holotype of Se. oblonga as 46 mm long and 39 mm wide, which is much larger than the specimens we examined in this study, with the length-to-width ratio of the carapace (CL/CW) being 1.18. This CL/CW ratio of our material tends to be larger in larger individuals: 1.06 in a male with CL 24.9 mm (ZRC 2008.0872), and 1.12 in a female with CL 32.4 mm (ZRC 2009.0320). This trend may explain why a very large specimen (e.g. holotype of Se. oblonga) has a CL/CW ratio of 1.18.

De Man (1889) described Sesarma trapezoideum var. longitarsis from Viti Island, Fiji, mainly on the basis of the difference in the proportion of ambulatory legs – that is, the dactylus of the P5 was almost as long as the propodus measured along the upper edge in his taxon (Figure 10) (vs somewhat shorter in the typical Se. trapezoideum) and the merus of the P5 was about two-thirds of the extraorbital width (about six-sevenths in typical Se. trapezoideum). Comparison between the holotype of Se. trapezoideum longitarsis (Figure 10) and the present material of Sh. trapezoideum, however, showed that there are no clear differences in the leg proportions. As such, Se. trapezoideum longitarsis remains a junior subjective synonym of Sh. trapezoideum .

Ecological note

In Sulawesi, Taiwan and the Ryukyus, Shinobium trapezoideum has been found on vertical or nearly vertical riverine cliffs or rocks from the lower limit of the freshwater area of a river (not brackish water) upwards. The crab is more active at night and usually observed clinging onto such cliffs or rocks, both under and above water, but is sometimes also collected from beneath rocks. The colour pattern of Sh. trapezoideum provides very effective camouflage, especially when it is on dark and moist cliff and rock surfaces covered with algae or mosses. It usually holds still on the surface when it is on the cliff or rock surfaces, but when disturbed, it moves swiftly around the surface and sometimes jumps into the water. See Jeng et al. (2003, p. 236, fig. 2a), Maenosono and Naruse (2016, p. 16) and Murata (2017, p. 11, fig. 2) for details.