Diogenes mixtus Lanchester, 1902

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 : 334-335

Diogenes mixtus Lanchester, 1902

( Figs. 3A, B , 4A )

Diogenes mixtus Lanchester, 1902: 367 , pl. 34, figs. 2, 2a, 2b (type locality: Pulau Bidan, Penang, Malaysia); Nobili, 1903: 16; McLaughlin & Clark, 1997: 45, figs. 7f, 8f, 9i, 13a; McLaughlin, 2002a: 424, figs. 5D, E, 6A.

Material examined. 2 males, 6.3– 5.1 mm ( ZRC 2021.0107 ), st. TB98, Eastern Bunkering A, 1°18.938′N 104°05.312′E, 30.2–33.6 m, 28 May 2013 ; 1 male, 5.8 mm ( MZB Cru 5199), Coney Island , otter trawl, 10–15 m, 8 March 2012 ; 1 male, 2.0 mm ( ZRC 2021.0108 ), st. DW28, Singapore Port Limit , Eastern Boarding Ground A, 1°13.181′N 103°52.900′E, 94.3–97.6 m, gravel, rock, 22 May 2013 ; 1 male, 3.1 mm ( ZRC 1990.4088 ), Pulau Tekong , 27 March 1987 ; 1 male, 9.1 mm ( ZRC 2021.0109 ), st. SW23, St John’s Island , 1°13.120′N 103°51.417′E, intertidal, 21 May 2013 ; 1 ovigerous female, 5.7 mm ( ZRC 2021.0110 ), DW17, Pulau Ubin , 1°25.110′N 103°55.722′E, 16 October 2012 ; 1 male, 8.0 mm ( ZRC 2021.0111 ), DW40, opposite Changi Chalet Radar , 1°23.797′N 103°58.751′E, 21– 15.6 mm, 19 October 2012 .

Colour in life. In general, light cream or pinkish cream ( Fig. 4A ). Carapace mottled brown and cream; shield mottled cream, dark and light brown on middle of dorsal surface; antennal peduncle cream with streak of greenish brown on distal part of fifth peduncular segment; antennular peduncle cream, longitudinal brown stripe on dorsal surfaces of penultimate and ultimate segments; ocular peduncle cream with longitudinal dark brown stripes on dorsal and lateral surfaces. Chelipeds cream, streak of dark brown on dorsal surface of dactyl proximally, on middle of palm, and distal part of carpus. P2 and P3 cream with streak of light brown on median part of propodi and carpi.

Distribution. Thailand, Malaysia, and Singapore; intertidal to depth of 97 m, on sandy, gravel-rock, and broken shell substrates.

Remarks. Diogenes mixtus belongs to the group 1 sensu Forest (1952), and is related to the six species, viz., D. alias McLaughlin & Clark, 1997 , D. custos ( Fabricius, 1798) , D. dubius (Herbst, 1804) , D. miles ( Fabricius, 1787), D. planimanus Henderson, 1893 , and D. violaceus Henderson, 1893 by the presence of bifurcate antennal acicle. Morphological characters that differentiate this species from the congeners include the deep bifurcate antennal acicles with the mesial and lateral forks reaching and well exceeding the distal margin of the fourth peduncular segment, the covering of sparse spines and stiff setae on the cheliped palms, with denser and longer tuft of stiff setae on the dactyl and fixed finger ( Fig. 3A ), and the long, slender dactyl of P2 and P3, and the presence of row(s) of small spines on the dorsal margin of the dactyls and propodi of P2 and P3 ( Fig. 3B ).

The living colour of the species is described and illustrated for the first time ( Fig. 4A ). The characteristic longitudinal stripes on the dorsal surface of the ocular peduncles, which are still preserved after preservation in ethanol, have already been mentioned by McLaughlin (2002a) for the specimens from Phuket. This species was reported from Singapore by Nobili (1903), but McLaughlin & Clark (1997) failed to reexamine Nobili’s specimens, thus the occurrence in Singapore has been uncertain. This study confirms the presence of this species in Singapore waters.

RAFFLES BULLETIN OF ZOOLOGY 2022

Figures

Fig. 3. A, B, Diogenes mixtus Lanchester, 1902, male, 8.0 mm (ZRC 2021.0111); C, D, Diogenes planimanus Henderson, 1893, male, 6.7 mm (ZRC 2021.0112). A, C, left cheliped, dorsal view; B, D, left P2 and P3, lateral view.

Fig. 4. A, Diogenes mixtus Lanchester, 1902, male, 8.0 mm (ZRC 2021.0111); B, Diogenes planimanus Henderson, 1893, male, 6.7 mm (ZRC 2021.0112).