Diogenes luteus, Rahayu, 2024

Rahayu, Dwi Listyo, 2024, Two new hermit crab species of the genus Diogenes Dana, 1851 from Lombok Island, Indonesia (Crustacea: Decapoda: Anomura: Diogenidae), Raffles Bulletin of Zoology 72, pp. 91-104 : 91-98

Diogenes luteus , new species

( Figs. 1B‒D , 2 , 3 )

Type material. Holotype, male, 2.2 mm ( MZB Cru 5754), 8° 24′ 02.8″N 1116° 05′ 07.4″E, Teluk [= Bay] Kombal, Lombok Utara [= North], 4 June 2023 . Paratypes, 4 males, 1.5–2.5 mm, 1 female, 1.8 mm, 2 ovigerous females, 1.5, 1.6 mm ( MZB Cru 5755) ; 5 males, 1.3‒2.5 mm, 1 ovigerous female, 1.6 mm ( ZRC 2023.0671 ), same locality as holotype . Other material. 2 males, 2.0, 2.4 mm, 2 females, 1.1, 1.5 mm, 1 ovigerous female, 1.6 mm ( MZB Cru 5756) ; 3 males, 1.3‒2.5 mm, 2 females, 1.5, 1.6 mm, 1 ovigerous female, 2.2 mm ( ZRC 2023.0672 ), same locality as holotype, 17 June 2023 ; 8 males, 2.0– 2.4 mm, Bedukang beach, Brunei Darussalam, 11 July 2020 .

Comparative material. Diogenes takedai Rahayu, 2012 , 1 male, 1.9 mm, Pandanan, Lombok, 25 October 2009 ( MZB Cru 3263).

Description. Shield ( Figs. 1B‒D , 2A ) approximately as long as broad; anterolateral margins sloping, each lined with minute spinulose granules, anterolateral angles each with small spine; dorsal surface slightly rugose, with some short, transverse, marginally spinulose ridges laterally and few tufts of short setae; posterior margin roundly truncate. Rostral lobe broadly rounded, weakly produced. Lateral projections triangular, not exceeding tip of rostral lobe, each with small terminal spine. Branchiostegite unarmed on dorsal margin; anterior margin rounded, unarmed.

Ocular peduncles ( Fig. 2A ) stout, left slightly longer than right, 0.6–0.7 length of shield, inflated proximally, narrowing distally to rounded cornea; surfaces almost glabrous. Corneas slightly dilated, diameter about 0.2 of peduncular length. Ocular acicles subtriangular, each with row of 4 or 5 spines on distolateral margin, distalmost spine strongest. Intercalary rostriform process simply acuminate at tip, not reaching tips of ocular acicles.

Antennular peduncles ( Fig. 2A ) unarmed, when fully extended, overreaching distal corneal margins by 0.7 length of ultimate article. Ultimate article 1.2 times as long as penultimate article, slightly widened in lateral view, with few moderately long setae on dorsal surface. Dorsal flagellum with short aesthetasc-bearing portion consisting of 5 or 6 articles.

Antennal peduncles stout ( Figs. 1B‒D , 2A ) overreaching distal corneal margins by half-length of article 5. Article 5 subcylindrical, unarmed, with row of long setae laterally. Article 4 with triangular dorsodistal margin, otherwise unarmed. Article 3 short, with few setae ventrally, unarmed. Article 2 stout, with dorsolateral distal angle produced into prominent spine, dorsomesial distal angle with small spine; ventral surface convex, with 4 marginal spines. Article 1 unarmed, with scattered short setae laterally. Antennal acicle short ( Fig. 2A, B ), stout, triangular, not reaching half-length of article 4, with row of 4 to 5 strong spines and short setae on oblique mesial margin. Antennal flagellum ( Fig. 1B‒D ) about 1.8 times as long as shield, not reaching and overreaching tip of left cheliped in males and females, respectively; each article distally with long lateral and mesial setae forming cast net-like structure, and sometimes with additional short seta dorsally.

Maxilliped 3 ( Fig. 2C ) moderately slender. Dactylus to merus unarmed; dactylus approximately as long as propodus; ischium with crista dentata composed of 4 small corneous spines, of which distalmost one strongest and slightly recurved; basis with 2 minutes spiniform denticles on mesial margin ( Fig. 2D ). Exopod overreaching midlength of carpus, with well-developed flagellum.

Chelipeds ( Fig. 1B‒D ) unequal and dissimilar, left much larger than right, but not particularly elongate even in males. Left cheliped ( Figs. 1B‒D , 2E‒G ) generally similar between male and female, but male with stronger spines on upper margin of palm; very narrow hiatus between dactylus and fixed finger; setation on chela and carpus quite sparse. Dactylus gently curving, slightly shorter than palm measured along upper margin; outer surface with row of moderately large spinulose tubercles adjacent to upper margin, and irregular rows of small spinulose tubercles on remaining portion; upper margin with row of small spines diminishing in size distally; inner surface with drop-like tubercles, larger proximally; cutting edge with 1 large, submedian blunt calcareous tooth followed by row of much smaller calcareous teeth, terminating in strong calcareous claw. Palm somewhat convex laterally on outer surface, approximately as broad as long measured along upper margin; outer surface covered with small and large tubercles, some tubercles drop-like, proximal and median tubercles larger; upper margin with row of small, forwardly directed spines; inner surface gently concave, smooth, nearly glabrous; fixed finger short, stout, with tufts of short setae on outer and inner surfaces; cutting edge with 1 large, blunt calcareous tooth medially and row of smaller teeth, terminating in strong calcareous claw. Carpus noticeably becoming wider distally; upper margin with row of strong spines; outer surface elevated in midline, with irregular rows of strong spines, and remaining portion with scattered spines and tubercles; lower margin with row of tubercles. Merus slightly shorter than carpus, longer than broad, with very low tubercles or protuberances on dorsal surface accompanied by sparse short setae; lateral surface with small, low tubercles; mesial surface nearly flat, with few small, low tubercles; ventral surface with small, low tubercles and scattered short setae. Ischium without conspicuous armature, with sparse short setae.

Right cheliped ( Figs. 1B‒D , 2H ) when fully extended, reaching to midlength of palm of left cheliped, covered with long and dense setae not obscuring armature. Dactylus gently curving, 1.3 times as long as palm measured along upper margin; upper margin with 2 rows of strong spines; outer surface with scattered spinules; cutting edge with row of very small, blunt calcareous teeth, terminating in small corneous claw. Palm covered with sparse small spines on entire surfaces, upper surface with row of large spines; outer surface sloping without distinct delimitation of upper margin; lower to inner surfaces glabrous, with few setae; fixed finger with row of minute blunt calcareous teeth on cutting edge, terminating in small corneous claw, crossing claw of dactylus; narrow hiatus between fingers. Carpus widened distally, with scattered tufts of long setae on outer surface; upper margin with row of spines increasing in size distally and followed by few low protuberances; outer surface with longitudinal row of small spines medially, few small, low protuberances on remaining portion; inner surfaces almost glabrous. Merus somewhat compressed laterally; dorsal margin with row of well-spaced small spines and tufts of short setae; lateral surface with few small, low protuberances, ventrolateral margin with 1 small subdistal spine; mesial surface almost glabrous, ventromesial margin with small distal spine followed by low protuberances; ventral surface narrow, with scattered long setae. Ischium unarmed, with sparse setae.

Pereopods 2 and 3 ( Fig. 3 ) generally similar, relatively slender. Dactyli subequal in length to propodi, slightly curved ventrally, but not twisted, each terminating in long corneous claw; dorsal margins each with row of sparse moderately long setae; lateral and mesial faces with few short setae, devoid of median sulci; ventral margins each with row of sparse moderately long setae. Propodi distinctly longer than carpi; dorsal margins without conspicuous armature, each with row of sparse, moderately long setae; lateral and mesial faces with tufts of short setae adjacent to dorsal and ventral margins; ventral surfaces each with row of widely spaced, moderately long setae. Carpi each with small dorsodistal spine and row of moderately long setae; lateral and mesial faces almost glabrous; ventral margins each with few moderately short setae. Meri each with row of sparse, moderately long setae on dorsal and ventral margins; lateral and mesial faces almost glabrous; ventral margins unarmed. Ischia each with row of sparse setae on dorsal and ventral margins. Female with paired gonopores on coxae of pereopods 3.

Pereopods 4 semichelate ( Fig. 2I ). Dactylus slightly curved distally, dorsodistally with long, dense setae. Propodi unarmed; propodal rasp occupying lateral face of fixed finger and extending onto ventral one-third of palm, consisting of numerous rows of small oval corneous scales. Carpi unarmed at dorsodistal angles.

Male with 4 well-developed, unpaired, uniramous left pleopods; pleopod 3 largest. Female also with 4 unpaired, biramous left pleopods.

Telson ( Fig. 2J ) with distinct median cleft and row of small spines on terminal margin, left lobe larger but not longer than right, lateral margin with row of large spines interspersed by smaller spines; right lobe unarmed on lateral margin; row of long setae on terminal margin extending onto lateral margins. Colour in life. See Fig. 1B‒D . Shield whitish cream, with brown patches on posteromedian part; branchial regions pinkish. Ocular peduncles dark brown proximally, followed by whitish cream area, dark brown band medially, followed by golden yellow distally, narrow dark brown band adjacent to cornea; cornea silvery black; ocular acicles dark brown, terminal spines white; intercalary rostral process dark brown. Antennular peduncle white in general; ultimate article with dark brown band distally and proximally, large dark brown spot medially; penultimate article with dark brown band distally; flagellum alternately translucent white and light brown. Antennal peduncle translucent white or cream, articles 4 and 5 each with large dark brown spot distally; flagellum alternately dark brown and golden yellow. Left cheliped palm dark brown, speckled with white; dactylus and fixed finger whitish cream; carpus and merus dark brown, tubercles white. Right cheliped palm whitish cream, speckled with light brown proximally; dactylus and fixed finger as in those of left cheliped; carpus and merus light brown, with whitish cream tubercles. Pereopods 2 and 3 generally cream; dactyli yellowish cream or orangish cream, with dark brown or black broad streak on each dorsolateral and ventrolateral margins proximally; propodi each with dark brown or black broad streak on each dorsolateral and ventrolateral margins medially and proximally; carpi each with dark brown or black broad longitudinal band on each lateral and dorsal faces not reaching distal area, smear of light brown distally on dorsolateral face; meri each with dark brown spot on distal, median, and proximal areas, respectively ( Fig. 1B ). In some paratypes, left cheliped whitish cream, with faint light brown speckles ( Fig. 1C ), or uniformly dark brown, only tips of dactylus and fixed finger white ( Fig. 1D ).

Etymology. The specific name is derived from the Latin ‘luteus’ (= yellow), in reference to the colouration of the ocular peduncle adjacent to the cornea.

Remarks. The short, truncate antennal acicle in the new species is a character shared with eight other species included in the edwardsi group: D. albimaculatus Landschoff & Rahayu, 2018 ; D. berduri Rahayu, 2021 ; D. dorotheae Morgan & Forest, 1991 ; D. guttatus Henderson, 1888 ; D. heteropsammicola Igawa & Kato, 2017 ; D. hothuisi Asakura & Tachikawa, 2010 ; D. takedai Rahayu, 2012 ; and D. tirmiziae Siddiqui & McLaughlin, 2003 . Diogenes luteus , new species, can be separated from these congeners by the stout and distally narrowing ocular peduncles with only slightly dilated corneas, the short and stout antennal peduncles reaching the tip of the left cheliped and with long and thick flagella and dense setae forming cast-net like structure, and the unarmed branchiostegite.

Other differences with the closely related species mentioned above are armaments of the palm of the left cheliped. It is covered with: small and large tubercles, some tubercles are drop-like in D. luteus , new species ( Fig. 2E‒G ); minutely crenulate tubercles, with larger tubercles or spines on slightly elevated median ridge in D. albimaculatus ( Landschoff & Rahayu, 2018: 270, fig. 1B); irregular longitudinal row of moderately small, broad tubercles on midline, with additional row of smaller tubercles between it and upper margin in D. berduri ( Rahayu, 2021: 163, fig. 1C); short to long, acute to blunt tubercles in D. dorotheae ( Morgan & Forest, 1991: 663, fig. 6a); circular, mushroom-shape, flattened tubercles in D. guttatus ( McLaughlin, 2004: 5, fig. 2A); small tubercles and double rows of blunt spines on midline in D. heteropsammicola ( Igawa & Kato, 2017: 7, fig. 2A); more or less granular or tubercular, sometime with row of strong spines on midline in D. holthuisi ( Asakura & Tachikawa, 2010: 138, fig. 4A, B); small and large drop-like tubercles, with longitudinal row of moderately larger tubercles on midline in D. takedai (Rahayu, 2012: 266, fig. 1C); small, drop-like, spinulose tubercles, sometimes just ovate tubercles in D. tirmiziae ( Siddiqui & McLaughlin, 2003: 960, fig. 2)

The colouration in life is also different among these species. Both D. luteus , new species and D. tirmiziae have a yellow distal area and median dark brown band of the ocular peduncle, but the shield is whitish cream, with brown patches in D. luteus , new species ( Fig. 1B‒D ), instead of having a brown transverse band as in D. tirmiziae ( Siddiqui & McLaughlin, 2003) . The ambulatory pereopods each have orange and red longitudinal stripes in D. albimaculatus and D. berduri ( Landschoff & Rahayu, 2018: fig. 3; Rahayu, 2021: fig. 2), proximal dark brown or greenish brown bands in D. takedai ( Fig. 1A ), and alternately transparent and brown colours in D. holthuisi ( Rahayu & Osawa, 2012: fig. 1B), respectively. However, in D. luteus , new species, the ambulatory pereopods are cream or yellowish cream, with dark brown or black streaks on the dorsolateral and ventrolateral margins of each article ( Fig. 1B‒D ).

No colouration was reported for D. guttatus and D. dorotheae , but morphological differences mentioned above separate them from the new species.

Distribution. Lombok Island, Indonesia, and Pulau Bedukang, Brunei Darussalam; intertidal.

Figures

Fig. 1. A, Diogenes takedai Rahayu, 2012 (not measured and sexed); B, Diogenes luteus, new species, holotype, male 2.2 mm (MZB Cru 5754); C, Diogenes luteus, new species, paratype, ovigerous female, 1.6 mm (ZRC 2023.0671); D, Diogenes luteus, new species, paratype, male, 2.5 mm (MZB Cru 5755).

Fig. 2. Diogenes luteus, new species, holotype, male, 2.2 mm (MZB Cru 5754). A, shield and cephalic appendages; B, left antennal peduncle (articles 1–4), ventral view; C, right maxilliped 3, lateral view; D, right maxilliped 3, ischium and basis, lateral view; E, left cheliped, chela and carpus outer view; F, same, chela, mesial view; G, same, merus, lateral view; H, right cheliped, chela and carpus, outer view; I, right pereopod 4, lateral view; J, telson, dorsal view. Scales, A, E‒H = 1 mm; B, C, D, I, J = 0.5 mm. Setae partially omitted.

Fig. 3. Diogenes luteus, new species, holotype, male, 2.2 mm (MZB Cru 5754). A, left pereopod 2, lateral view; B, left pereopod 3, lateral view. Scales = 1 mm. Setae partially omitted.