Diogenes rectimanus Miers, 1884

Rahayu, Dwi Listyo, 2022, Hermit crabs of Singapore (Crustacea: Decapoda: Anomura: Diogenidae, Paguridae), with description of two new species, Raffles Bulletin of Zoology 70, pp. 329-363 : 348-349

Diogenes rectimanus Miers, 1884

( Fig. 8F )

Diogenes rectimanus Miers, 1884: 262 , pl. 27, fig. c (type locality: Prince of Wales Channel, Torres Strait); McLaughlin & Clark, 1997: 37, fig. 10b; McLaughlin, 2002a: 414, fig. 2A–C; Asakura, 2020: 6, figs. 18–21.

? Diogenes rectimanus – Henderson, 1893: 419; Alcock, 1905b: 71, pl. 6, fig. 8, 8a, pl. 7, fig. 2, 2a.

Not Diogenes rectimanus – Lanchester, 1902: 366.

Material examined. 1 male ( ZRC 1991.9678 ), Pulau Semakau ; 1 female, 1.5 mm ( ZRC 2021.0161 ), Between Pulau Hantu, Semakau and Senang, 1°13.437′N 103°44.521′E ‒ 1°13.526′N 103°44.634′E, Rectangular dredge, sand, 10.3– 6.4 m, 13 March 2013 ; 3 males, 1.5–2.2 mm ( ZRC 2021.0162 ), st. D05, Henderson Shoal , dredge, sand and mud, 7 m, 6 March 2012 ; 6 males, 0.9–3.6 mm, 2 females, 2.4 mm, 2.7 mm, 1 ovigerous female, 1.1 mm ( ZRC 2021.0163 ), st. D06, between Pulau Ubin and Pulau Tekong , sand and mud, dredge, 16 m, 6 March 2012 ; 1 male, 2.4 mm ( ZRC 2021.0164 ), st. D07, 1°25.189′N 103°58.630′E, 6 March 2012 ; 1 male, 2.2 mm ( MZB Cru 5206), st. TB106, 01°15.588′N 103°51.527′E, dredge, 17.2–18 m, 21 March 2013 ; 3 males, 2.9–4.0 mm, 1 female, 3.5 mm, Bedok Sea , 27 April 1982 ; 2 males, 4.2–4.5 mm, 1 female, 3.9 mm, 1 ovigerous female, 4.2 mm ( ZRC 2021.0165 ), Chek Jawa, 1 July 2009 ; 1 male, 1.5 mm ( ZRC 2021.0166 ), st. DR327, between Changi beach and Tekong, 01°23.420′N 104°00.459′E, sandy, muddy, 24.4–26.7 m, 19 March 2014 .

Distribution. Gulf of Aden, India, Sri Lanka, Thailand, Singapore, Malaysia, Arafura Sea, and Torres Strait; 6−27 m, on sandy muddy substrates.

Remarks. Most of the specimens examined in this study have the ocular peduncles being about 0.7 times as long as shield and having a small, not dilated cornea (about 0.3 times as long as ocular peduncles), the propodi of P2 and P3 devoid of dorsal spines and the carpi with a row of spines on the dorsal surface of P2 only, whereas on P3 only bearing a dorsodistal spine. According to the redescrition of the holotype by McLaughlin & Clark (1997), the ocular peduncle is 0.8 times as long as the shield; the P2 and P3 propodi and carpi are all armed with a row of small spines. However, the present specimens agree with the holotype in every diagnostic aspect, such as the presence of a row of strong, outwardly directed spines on the ventral margin of the palm of the left cheliped, sometimes extending onto proximal margin parallel to the carpal articulation, the presence of a longitudinal row of strong curved spines on the upper margin of the palm, and the presence of a strong spine on the lower distal angle of the left cheliped carpus, and the presence of long spines interspersed with smaller spines on the lobes of telson.

One small specimen found in a scaphopod shell has a straight abdomen with almost symmetrical telson. This variation could be in response to the habitat structure, also seen in other hermit crab species using straight shaped carcinoecia ( Lemaitre et al., 2018). The specimens of this study were collected from sandy, sandy-mud substrates.

Figures

Fig. 8. A, Diogenes avarus Heller, 1852, not collected, IT86, Cyrene Reef, 1°15.374′N 103°44.816′E, 27 May 2013; B, Diogenes fasciatus Rahayu & Forest, 1995, male, 5.3 mm (ZRC 2021.0132); C, Diogenes klaasi Rahayu & Forest, 1995, male, not collected, Singapore Strait; D, Diogenes laevicarpus Rahayu, 1996, male, 5.1 mm (ZRC 2021.0139); E, Diogenes moosai Rahayu & Forest, 1995, male, 1.8 mm (ZRC 2021.0160); F, Diogenes rectimanus Miers, 1884, male, not collected, DW58, East of Pulau Tekong, 01°25.064′N 104°04.992′E, 10.9–11.3 m, 22 October 2012.