Diogenes laevicarpus Rahayu, 1996

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 : 344

Diogenes laevicarpus Rahayu, 1996

( Fig. 8D )

Diogenes laevicarpus Rahayu, 1996: 341 , fig. 1 (type locality: Singapore); McLaughlin et al., 2010: 21 (list).

Material examined. 1 female, 4.2 mm ( ZRC 2021.0138 ), st. M18, End of Jalan Durian , 7 March 2012 ; 1 male, 5.1 mm ( ZRC 2021.0139 ), st. DW17, Pulau Ubin , 12 October 2012 ; 1 male, 2.2 mm ( ZRC 2021.0140 ), st. MF58, Pasir Ris 01°22.955′N 103°57.130′E, 11 May 2012 ; 2 females, 2.0 mm, 2.7 mm, 2 ovigerous females, 3.6 mm, 2.5 mm ( ZRC 2021.0141 ), st. DW36, Pulau Serangoon , 1°24.545′N 103°55.992′E, 16–18.6 m, 19 October 2012 ; 2 males, 3.2 mm, 3.5 mm ( ZRC 2021.0142 ), Changi , 16 February 1995 ; 1 female, 3.1 mm ( ZRC 1994.4412 ), Kallang basin, 15 December 1994 ; 4 males, 2.4–3.3 mm, 2 ovigerous females, 2.5 mm, 2.7 mm ( ZRC 2021.0144 ), Singapore Strait , June 2013 ; 2 males, 2.00 mm, 2.7 mm, 1 female, 2 mm, 1 ovigerous female, 3.1 mm ( ZRC 2021.0145 ), st. D07, Pulau Ubin , 6 March 2012 ; 1 male, 6.2 mm ( ZRC 2021.0146 ), st. MF48, Sarimbun Beach , 01°26.279′N 103°41.915′S, 14 February 2012 ; 23 males, 1.8–6.0 mm, 8 females, 1.8–3.3 mm, 12 ovigerous females, 2.4–4.4 mm ( ZRC 2021.0148 ), Chek Jawa , 1 July 2009 ; 3 males, 3.1–4.2 mm ( ZRC 2021.0149 ), st. DW58, East Pulau Tekong , 01°25.064′N 104°04.992′E, 10.9–11.3 m, 22 October 2012 ; 1 male, 4.7 mm, 5 females, 1.6‒3.8 mm ( ZRC 2021.0150 ), Red Cliff shoal area, Changi, 16 November 2008 ; 1 male, 5.3 mm ( ZRC 2021.0147 ), st. DW40, Opposite Changi Chalet Radar , 01°23.797′N 103°58.751′E, 19 October 2012 ; 1 female, 1.8 mm, 1 ovigerous female, 2.5 mm ( ZRC 2021.0143 ) .

Colour in life. Shield light brown, mottled with dark brown and bluish white; ocular peduncles generally tan with tinge of light brown distally, dark brown proximally; antennular peduncles transparent with dark brown spot proximally on dorsal surface of ultimate and penultimate segments; antennal peduncles light brown or tan with dark brown streak on second segment. Chelipeds mottled with tan and white, dark brown blotch on carpus and merus. P2 and P3 generally light brown, dactyls reddish brown, propodi with dark brown transverse band medially, longitudinal dark brown stripe ventromesially; carpi and meri with two large greenish brown longitudinal stripes on lateral face, dorsal face with large brown marking ( Fig. 8D ).

Distribution. Singapore, intertidal, on sandy muddy substrate.

Remarks. The specific characteristics of this species include: shield as long as broad, antennular peduncles slightly overreach antennal peduncles; outer surface of the left cheliped dactyl with broad longitudinal sulcus flanked by row(s) of tubercles; outer suface of left cheliped palm with spinous or drop-like tubercles crest extending from proximoventral angle, parallel with carpal articulation then curving distally along midline, reaching only to proximal 0.2, crest terminating abruptly, replaced by rows of small flattened tubercles, continued to almost reaching articulation with dactyl; longitudinal row of small spines or tubercles on outer surface of left cheliped palm between median row of tubercles and upper margin of palm; lower margin of left cheliped palm with row of tubercles; convex fixed finger of left chela covered by spines/tubercles that form broad longitudinal ridge.

Diogenes laevicarpus was described from two specimens with 2 mm shield length. Examination of 76 specimens in this study showed morphological variation on the armature of the ambulatory legs that related to the size of the animal. In the small specimens (sl ≤ 2.5 mm), the dorsal margin of each carpus of P2 is armed with a row of spinules and sometimes spinules are also detected on the propodus, while in P3 the propodi are usually unarmed and the carpi each bear a dorsodistal spine. In the larger specimens (sl> 2.5 mm), the dorsal margins of propodi and carpi of P2 and P3 bear a row or rows of spines, although the spines are smaller on P3.

The differences of this species with D. lophochir and D. costatus discussed by Rahayu (1996) were only on the proportion of the antennal and antennular peduncles against the ocular peduncles, and the presence of row of spines on the dorsal margins of the propodus and carpus of the ambulatory legs. As mentioned earlier, the presence of row of tubercles on the dorsal margin of the propodus and carpus of the ambulatory legs in this species is variable, therefore this character cannot be used to distinguish these three species. Although McLaughlin (2002b, 2005) showed that the proportion of antennal and antennular peduncles against ocular peduncles is variable and unreliable to separate the species in the genus Diogenes , this proportion is constant in all sizes of D. laevicarpus . Other left cheliped characters of D. costatus and D. lophochir that separate them from D. laevicarpus are as follows: dactyl without longitudinal sulcus; outer surface of palm without row of spines between medial crest and upper margin; fixed finger deflexed, without longitudinal ridge in D. costatus , with pronounced, narrow longitudinal ridge in D. lophochir .

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.