Diogenes kombalensis, 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 : 98-103

Diogenes kombalensis , new species

( Figs. 4‒6 )

Type material. Holotype, male, 3.3 mm ( MZB Cru 5757), 8° 24′ 02.8″N 1116° 05′ 07.4″E, Teluk (=Bay) Kombal, Lombok Utara (=North), 20 May 2023 . Paratypes, 6 males, 2.0– 3.1 mm, 2 females, 2.0, 2.2 mm, 4 ovigerous females, 2.2–2.7 mm ( MZB Cru 5758), 1 ovigerous female, 2.8 mm ( MZB Cru 5759) ; 6 males, 2.0– 3.6 mm, 2 females, 1.7, 2.7 mm, 4 ovigerous females, 1.8–2.0 mm ( ZRC 2023.0673 ) same locality as holotype .

Other material. 7 males, 1.7–3.1 mm, 3 females, 1.6–2.2 mm, 3 ovigerous females, 2.2–2.4 mm ( MZB Cru 5760) , 8 males, 1.8–3.3 mm, 3 females, 1.6–2.4 mm, 3 ovigerous females, 2.2–2.7 mm ( ZRC 2023.0674 ), same locality as holotype, 4 June 2023 .

Description. Shield ( Figs. 4 , 5A ) approximately as long as broad; anterolateral margins sloping, lined with minute spinulose granules, anterolateral angles each with small spine; dorsal surface rugose, with short, transverse, marginally spinulose ridges laterally and few tufts of short setae. Rostral lobe broadly rounded, weakly produced. Lateral projections triangular, exceeding tip of rostral lobe. Branchiostegite with row of 6–9 strong spines on dorsal margin; anterior margin rounded, unarmed, but with long setae.

Ocular peduncles ( Fig. 5A ) stout, left and right equal in length, 0.7–0.8 length of shield, not inflated basally, with sparse setae dorsally and mesially. Corneas very slightly dilated, diameter about 0.3 of peduncular length. Ocular acicles slightly concave on mesial margin; anterolateral margin with row of spines, decreasing in size proximally. Intercalary rostriform process simply acuminate at tip, barely reaching tips of ocular acicles.

Antennular peduncles ( Fig. 5A ) unarmed, when fully extended, overreaching distal corneal margins by half length of ultimate article. Ultimate article 1.4 times as long as penultimate article, slightly widened distally in lateral view, with sparse moderately short setae on dorsal surface; basal article with long setae on dorsodistal mesial angle and on proximal mesial margin. Dorsal flagellum with short aesthetasc-bearing portion consisting of 6 articles.

Antennal peduncles slender ( Fig. 5A ), when fully extended, overreaching distal corneal margins by 0.7 length of article 5. Article 5 subcylindrical, unarmed, with row of long setae laterally and sparse short setae dorsally. Article 4 with triangular dorsodistal margin, otherwise unarmed. Article 3 short, unarmed, with few setae ventrally. Article 2 stout, with dorsolateral distal angle produced into prominent spine; dorsomesial distal angle with small spine; ventral surface convex, unarmed. Article 1 unarmed, with scattered short setae laterally. Antennal acicle reaching distal margin of article 4, terminating in strong spine, bearing row of 4 or 5 spines and long setae on mesial margin. Antennal flagellum ( Fig. 4 ) about 2 times as long as shield, reaching half-length of palm of left cheliped; each article distally with long lateral setae and sometimes with additional short seta.

Maxilliped 3 ( Fig. 5B ) moderately slender. Ischium with crista dentata composed of 2 small corneous spines, distal spine slightly recurved ( Fig. 5C ). Merus to dactylus unarmed; dactylus approximately as long as propodus. Exopod reaching proximal third of carpus, with well-developed flagellum.

Chelipeds ( Figs. 4 , 5D‒H ) unequal and dissimilar, left much larger than right, elongate in large males. Left cheliped of male ( Figs. 4 , 5D‒G ) with narrow hiatus between dactylus and fixed finger; setation on chela and carpus quite sparse. Dactylus relatively broad, flattened, gently curving, approximately as long as palm measured along upper margin; upper margin with double rows of large spinulose tubercles decreasing in size distally; outer surface with row of small spinulose tubercles adjacent to upper margin, narrow sulcus between this row and upper margin, remaining portion with scattered tubercles, larger, flattened tubercles adjacent to cutting margin proximally; cutting edge with 1 large, blunt calcareous tooth submedially and row of smaller calcareous teeth, terminating in strong calcareous claw; inner surface with median longitudinal row of tubercles becoming larger proximally, moderately deep sulcus between this row and upper margin, scattered flattened tubercles adjacent to cutting edge. Palm about as broad as long measured along upper margin; outer surface somewhat convex, covered with small tubercles, median longitudinal broad crest composed of rows of larger tubercles starting from median proximal margin and reaching midlength of palm; upper margin with row of large spinulose tubercles; inner surface gently convex, covered with flattened tubercles, larger tubercles along lower margin, sparse long setae near upper margin; fixed finger short, gently deflexed, covered with small tubercles denser adjacent to lower margin; cutting edge with 1 large, blunt calcareous tooth submedially following by row of smaller teeth, terminating in strong calcareous claw. Carpus slightly becoming wider distally; upper margin with double row of strong spines; outer surface convex, covered with moderately large tubercles. Merus slightly shorter than carpus, longer than broad, with row of small spines on dorsal margin accompanied by sparse short setae; lateral surface with short transverse rows of low tubercles; mesial surface nearly flat, with few small, low tubercles; ventral surface with transverse rows of small tubercles and scattered short setae. Ischium without conspicuous armature, only with sparse short setae. Left cheliped of female generally similar to that of male, but with weaker spines on upper margin of palm.

Right cheliped ( Figs. 4 , 5H ) reaching to distal margin of carpus of left cheliped when fully extended, covered with long setae not obscuring armature; broad hiatus between dactylus and fixed finger. Dactylus gently curving, 2.1 times as long as palm measured along upper margin; upper margin with 2 rows of strong spines, coalescent and becoming very small distally; outer surface with short row of spinules in proximal midline, longitudinal furrow adjacent to upper margin, remaining portion with scattered spinules; cutting edge with row of very small, blunt calcareous teeth, terminating in small corneous claw. Palm with row of large spines on upper margin; outer surface with few large spines near upper margin, remaining portion with scattered spinules; lower margin with row of spines continued onto fixed finger; fixed finger with row of minute blunt calcareous teeth on cutting edge, terminating in small corneous claw, crossing claw of dactylus. Carpus widened distally, with scattered tufts of long setae; upper margin with row of spines increasing in size distally; outer surface with scattered spines, distal margin with row of small spines. Merus somewhat compressed laterally; dorsal margin with row of small spines and short setae; lateral surface with transverse rows of flattened tubercles, ventrolateral margin with low protuberance; mesial surface glabrous, ventromesial margin with row of small tubercles; ventral surface narrow, with transverse rows of flattened tubercles and scattered long setae. Ischium unarmed, with sparse setae.

Pereopods 2 and 3 ( Fig. 6 ) generally similar, relatively slender. Dactyli 1.4 times as long as propodi, slightly curved ventrally, but not twisted, each terminating in small corneous claw; dorsal margins each with row of sparse, moderately long setae; lateral and mesial faces with few short setae, median sulcus along lateral face; 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 faces with tufts of long setae adjacent to dorsal margins; mesial surfaces with sparse long setae; ventral surfaces each with row of widely spaced, moderately long setae. Carpi each dorsally with row of moderately long setae, and with row of moderately large spines (pereopods 2) and tiny spines on distal half (pereopods 3); lateral and mesial faces almost glabrous; ventral margins with few moderately short setae. Meri each with row of sparse, moderately long setae on dorsal and ventral margins; dorsal margins each with row of small spines on half distal (pereopods 2) and unarmed (pereopods 3); lateral and mesial faces almost glabrous; ventral margins unarmed. Ischia each with row of setae on dorsal and ventral margins. Female with paired gonopores on coxae of pereopods 3.

Pereopods 4 semichelate ( Fig. 5I ). Dactylus with long, dense setae dorsodistally. Propodi unarmed; propodal rasp occupying lateral face of fixed finger and extending onto distal third of palm, consisting of numerous rows of small oval corneous scales. Carpi each with small spine at dorsodistal angle.

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

Telson ( Fig. 5J ) with indistinct median cleft and row of small spines on terminal margin; left lobe larger and 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. 4 . Shield dark or light brown, speckled with bluish white. Ocular peduncles cream, triangular brown area on dorsal surface starting from mesial base of cornea to proximal part of peduncle; lateral and mesial surfaces each with dark brown spot medially; dark brown band on base of cornea; ocular scale brown, with some white spots. intercalary rostral process dark brown. Antennular peduncles cream, with dark brown mark on distal margin of each article. Antennal peduncles cream or white speckled with dark brown, antennal acicle brown, spines white; antennal flagella alternately dark brown and cream. Left cheliped dark brown, partially speckled with white or orange, spines white or light brown; cutting edge of fixed finger white. Right cheliped white on dactylus and fixed finger; palm whitish cream, speckled with dark brown; carpus whitish cream distally, dark brown proximally; merus light brown. Pereopods 2 and 3 generally cream; dactyli greenish cream or light brown, with faint dark brown band proximally; propodi cream or whitish cream, with large dark brown band medially and narrower light brown bands distally and proximally; carpi and meri light brown, each with dark brown band medially and lighter brown bands distally and proximally, surface between bands speckled with light brown ( Fig. 4A ). In some paratypes, left cheliped orangish brown, cutting edges white ( Fig. 4B ) or white speckled with light brown ( Fig. 4C ); right cheliped light brown, dactylus and fixed finger white, with tinge of orange or pink, spines white. Pereopods 2 and 3 orangish cream; dactyli and propodi cream or orangish cream, propodi each with large dark brown band medially and narrower light brown bands distally and proximally; carpi and meri light brown, each with dark brown band medially and lighter brown bands distally and proximally, surface between bands speckled with light brown ( Fig. 4B, C ).

Etymology. The new species is named after the type locality, Teluk [= Bay] Kombal, in the northern coast of Lombok Island.

Remarks. In having stout ocular peduncles that reach only half the length of the ultimate article of the antennular peduncles and half the length of the fifth article of the antennal peduncles, and the presence of a median crest on the outer surface of the left cheliped palm, D. kombalensis , new species, closely resembles D. chhapgari Trivedi, Osawa & Vachhrajani, 2016 , D. foresti Rahayu & Hortle, 2002 , and D. singaporensis Rahayu, 2015 . Diogenes chhapgari differs from D. kombalensis , new species in the armament of the left cheliped palm. In D. chhapgari , the median longitudinal crest on the outer face of the left cheliped palm is strongly elevated, becomes stronger and wider distally, and reaches beyond half the length; and the inner surface has two longitudinal ridges of large tubercles ( Trivedi et al., 2016: fig. 2A, B). In D. kombalensis , new species, the longitudinal median crest is broad, consists of several rows of spines, and reaches only to the midline of the palm; and the inner face of the palm is covered with low flattened tubercles, larger tubercles on lower margin, but lacks longitudinal ridges of tubercles ( Fig. 5D, H ). The colour in life is also different between the two species. The dactyli and carpi of the ambulatory pereopods of D. chhapgari are generally cream, each with a light orange band ( Trivedi et al., 2016: 195); while those of D. kombalensis , new species, are generally light or dark brown, each with a dark brown band ( Fig. 4 ).

Diogenes foresti differs from the new species in the following characters: ocular peduncles stout, dilated proximally and on corneas; left cheliped palm with median longitudinal rows of tubercles and a proximal strong crest consisting of small tubercles on the outer surface; pereopod 2 and 3 slender, with dactyli 1.6 times as long as propodi and carpi unarmed on dorsal surfaces ( Rahayu & Hortle, 2002: fig. 1). In D. kombalensis , new species, the ocular peduncles are slightly dilated on the cornea, but not dilated proximally; the left cheliped palm lacks a proximal strong crest of small tubercles; and the pereopod 2 and 3 have dactyli 1.4 times as long as propodi and carpi each with a row of spines on the dorsal margin ( Figs. 5A, D , 6 ).

Diogenes singaporensis is distinguished from the new species by having strong spines on the article 4 of the antennal peduncle and longitudinal rows of spines on the inner surface of palm (such rows are absent in D. kombalensis , new species); and the antennal and antennular peduncles being somewhat longer. They overreach the distal margin of the corneas by the whole length of the distal articles of the antennular and antennal peduncles ( Rahayu, 2015: 3 A, F; Fig. 5A, H ), instead of reaching beyond it only by the half length of the latter ones in D. kombalensis , new species ( Fig. 5A ).

Distribution. At this moment, found only in Teluk Kombal, on the northern coast of Lombok Island, Indonesia.

Figures

Fig. 4. Diogenes kombalensis, new species. A, holotype, male 3.3 mm (MZB Cru 5757); B, paratype, ovigerous female, 2.8 mm (MZB Cru 5759); C, paratype, male, 3.6 mm (ZRC 2023.0673).

Fig. 5. Diogenes kombalensis, new species, holotype, male, 3.5 mm (MZB Cru 5757). A, shield and cephalic appendages; B, right maxilliped 3, lateral view; C, right maxilliped 3, ischium and basis, lateral view; D, left cheliped, chela and carpus, outer view; E, same, merus, lateral view; F, same, chela, mesial view; G, same, inner view; H, right cheliped, chela and carpus, outer view; I, left pereopod 4, lateral view; J, telson, dorsal view. Scales, A, B, D‒J = 1 mm; C = 0.5 mm. Setae partially omitted.

Fig. 6. Diogenes kombalensis, new species, holotype, male, 3.5 mm (MZB Cru 5757). A, left pereopod 2, lateral view; B, left pereopod 3, lateral view. Scales = 1 mm. Setae partially omitted.