Diogenes fasciatus Rahayu & Forest, 1995

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 : 342-343

Diogenes fasciatus Rahayu & Forest, 1995

( Fig. 8B )

Diogenes fasciatus Rahayu & Forest, 1995: 388 , fig. 1 (type locality: Muara Karang, Jakarta Bay, Indonesia); Rahayu, 1996: 340; Siddiqui, Kazmi & McLaughlin, 2004: 185, fig. 13.

Material examined. 96 males, 0.7–2.9 mm, 5 females, 1.8–2.5 mm, 20 ovigerous females, 1.8–2.5 mm ( ZRC 2021.0130 ), Changi , 18 January 1995 ; 20 males, 2.4–4.2 mm, 12 females, 1.6–2.4 mm, 20 ovigerous females, 1.6–2.9 mm ( ZRC 2021.0131 ), Changi , 16 February 1995 ; 8 males, 2.3‒5.3 mm ( ZRC 2021.0132 ), DW58, East of Pulau Tekong , 01°25.064′N 104°04.992′E, 10.9–11.3 m, 22 October 2012 ; 15 males, 1.6–2.2 mm, 4 females, 1.6–2.0 mm, 5 ovigerous females, 1.8–2.0 mm ( ZRC 2021.0133 ), Chek Jawa , 21 September 2001 ; 1 male, 1.0 mm ( ZRC 2021.0134 ), Pulau Hantu , 7–10 m, 16 December 2012 ; 1 male, 3.9 mm ( ZRC 2021.0135 ), st. M24, Pulau Ketam , 8 March 2012 ; 1 ovigerous female, 4.5 mm ( ZRC 2021.0136 ), st. M13, Pulau Ubin , 7 March 2012 ; 7 males, 4.5–6.0 mm ( ZRC 2021.0137 ), Changi , beach seine, 16 July 1993 ; 3 males, 3.1–4.2 mm, 3 females, 2.5–3.5 mm, Perak, Malaysia .

Colour in life. Shield mottled with dark grey and light brown. Ocular peduncle white with greyish brown blotch on dorsomesial face distally, light brown patch proximally. Antennular peduncle generally greyish brown, with dark brown band on distal margin of ultimate and penultimate segments, flagella white; first to fourth segments and antennal acicle of antennal peduncle greyish brown, fifth segment and flagella white. Chelipeds palm whitish grey; dactyl and fixed finger with tint of light brown, carpi and meri dark brown or dark grey. P2 and P3 dark brown or dark grey, lighter grey dorsally and ventrally on propodi and carpi, with white spot on articulation dactyl, propodus and carpus ( Fig. 8B ).

The general colouration in life varies from yellowish light brown to dark brown or dark grey, but the pattern is the same.

Distribution. Pakistan, Singapore, Malaysia, and Indonesia; 0–7 m, inhabit sandy, muddy substrate.

Remarks. Among the species in the edwardsii group, this species is readily recognised by an ensemble of characters as follows: antennal peduncles stout, flagellum with abundant setae; left cheliped dactyl broad, flattened, covered with small tubercls; fixed finger outer surface tuberculate and devoid of longitudinal ridge; and palm with row of strong spines on upper and lower margins, at proximoventral angle row of strong spines parallel to carpal articulation, reaching to distal quarter, then continued as longitudinal row/rows of small spines on outer surface. The differences between D. fasciatus , D. avarus Heller, 1865 , and D. investigatoris Alcock, 1905b were already discussed by Rahayu & Forest (1995), and the significance of those characters has been confirmed. The flattened dactyl of the left cheliped and the presence of a row or rows of spines on the propodi of P2 and P3 placed D. fasciatus close to D. lophochir Morgan, 1989 . But these two species differ in the presence of pronounced ridge on the fixed finger of the left cheliped in D. lopochir (absence in D. fasciatus ), the tuberculate crest on the outer face of the palm of the left cheliped is positioned in the midline in D. lophochir while in D. fasciatus this crest is located adjacent to upper margin.

Rahayu & Forest (1995) did not mention the presence of row of spines on the dorsal margin of the propodi of P2 and P3 but indicated that the spines on the carpi are present only in the large individual. Siddiqui et al. (2004) stated that these spines are present or absent in their material and that the specimens from Pakistan have one or two rows of spines on carpi, while Asakura (2020) stated that, in the material from Singapore and Thailand, the dorsal margins of propodi of ambulatory legs have a row of spines, and also figured the spines on the dorsal margin of carpi ( Asakura, 2020: fig. 11A, C, E). In some specimens in this study, the propodi and carpi of P2 and P3 have one or two rows of spines on the dorsal margin. Additionally, a tiny spine on the dorsodistal margin of the fourth segment of the antennal peduncles was also detected in some individuals. The spines on the mesial margin of the antennal acicle varies from very prominent to moderately large, and one additional spine is sometimes present at the midlength of the lateral margin. The same character was also observed by Asakura (2020) in his specimens. Further study is necessary to confirm that these characters mentioned above are merely attributed to intraspecific variations or interspecific differences.

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.