Diogenes matabiru, Rahayu & Pratiwi, 2022

Rahayu, Dwi Listyo & Pratiwi, Rianta, 2022, Diogenes matabiru, a new species of hermit crab from Lombok Island, Indonesia (Crustacea, Decapoda, Anomura, Diogenidae), Zootaxa 5093 (4), pp. 493-500 : 494-498

Diogenes matabiru n. sp.

Material examined. Holotype, male, 2.7 mm ( MZB Cru 5343), Jerowaru, Lombok Island , coll. R. Pratiwi, 29 September 2014 . Paratype, male, 2.5 mm ( ZRC 2021.0900 ), same locality as holotype .

Comparative material. Diogenes pallescens Whitelegge, 1897 . 1 ovigerous female, 1.8 mm ( MZB Cru 5344), Kuta, Lombok , June 2007; 1 ovigerous female, 2.5 mm ( MZB Cru 5345), Tanjung Merah , Sulawesi, 31 March 2003 ; 1 male, 2.4 mm, 1 female, 1.3 mm ( MZB Cru 5346), Medana, Lombok , 24 July 2006 ; 1 female, 2.0 mm, 1 ovigerous female, 2.7 mm ( MZB Cru 5347), Teluk Kodek, Lombok , 20 August 2021 .

Diogenes biramus Morgan, 1987 . 1 female, 2.7 mm ( MZB Cru 5348), Sekotong, Lombok , 16 May 2007 ; 1 female 4.9 mm ( MZB Cru 5349), Medana, Lombok , 12 June 2007 ; 1 female, 2.0 mm ( ZRC 2021.0901 ), Pulau Osi, Seram , Maluku, 16 June 1989 ; 1 female, 1.8 mm ( ZRC 2021.0902 ), Medana, Lombok , 2 September 2021 .

Diogenes viridis Haig & Ball, 1988 . 1 ovigerous female, 2.2 mm, Santo , Vanuatu, 4 October 2006 ( MNHN).

Description. Shield ( Figs. 1A , 2A ) about 1.2 times as long as broad; anterior margin between rostral lobe and lateral projections somewhat concave; anterolateral angle rounded, margin sloping; posterior margin truncate; dorsal surface with scattered spines, prominent spines along lateral margin, and tufts of sparse setae. Rostrum broadly rounded. Lateral projections triangular, exceeding tip of rostral lobe, each with moderately large marginal spine. Dorsal margins of branchiostegites with row of 4 or 5 small spines.

Ocular peduncle ( Figs. 1A , 2A ) slender, cylindrical, approximately as long as shield, inflated proximally, with tufts of very sparse setae dorsoproximally; cornea not dilated, diameter about 0.2 times peduncular length. Ocular acicles broad, subrectangular, basally separated by approximately 0.3 width of 1 acicle, with row of spines on terminal margin, mesialmost spine largest. Intercalary rostral process slender, simple at tip, overreaching tip of mesial spine of ocular acicle, with few long setae; no ventral spine.

Antennular peduncle ( Figs. 1A , 2A ), when fully extended, not reaching cornea. Ultimate and penultimate segments glabrous. Basal segment with 2 or 3 small spines on ventrolateral distal margin

Antennal peduncle ( Fig. 1A ) reaching 0.5 length of ocular peduncle; fifth segment with 1 long and 1 short setae distally, fourth segment with few short setae distally, third segment short, stout, also with few short setae, second segment with dorsolateral distal angle produced into prominent spine, dorsomesial distal angle unarmed, small spine on dorsodistal margin medially, mesial and lateral margins with few setae, first segments unarmed. Antennal acicle overreaching distal margin of fourth segment, terminating in strong spine; lateral margin with 1 large spine, mesial margin with 3 moderately large spines, and few setae. Antennal flagellum slightly longer than shield, consisting of 16–18 articles, each with 1 or 2 simple setae.

Third maxilliped ( Fig. 1B ) with coxa and basis unarmed; crista dentata on ischium obsolete; merus longer than carpus, both segments with long setae on mesial margin, lateral margin with fewer setae; propodus slightly longer than carpus; dactyl shorter than propodus, both with setae ventrally.

Left cheliped ( Figs. 1C , 2A ) larger than right, narrow hiatus between dactyl and fixed finger. Dactyl about 0.8 times as long as upper margin of palm, slightly arched; cutting edge with row of blunt calcareous teeth, 1 large tooth proximally, terminating in small calcareous claw, slightly overlapped by fixed finger; outer surface convex with partial covering of spines, and with long stiff setae; upper margin with 2 rows of moderately large spines decreasing in size distally; inner surface slightly convex, with covering tubercles and tufts of short setae. Fixed finger outer surface slightly convex, armed with moderately large sharp and blunt spines and long stiff setae; lower margin with row of moderately small, subacute spines, forming weak curve with lower, similarly armed margin of palm; cutting edge of fixed finger with row of calcareous teeth, large tooth subproximally, terminating in large calcareous claw; inner surface with scattered small tubercles and few tufts of short setae. Palm slightly shorter than carpus, with row of moderately large spines on upper margin, second row shorter and with smaller spines; outer surface convex, with sparse short setae, longitudinal row of sharp, large spines on midline, extending beyond midlength of palm but not reaching articulation with dactyl; additional longitudinal row of small spines between midline and upper margin merging into scattered spines adjacent to articulation with dactyl; lower half of outer surface with sparse spines forming irregular longitudinal rows; inner surface with few small tubercles and short setae. Carpus as long as merus; upper margin with row of irregularly spaced prominent spines and sparse long setae; outer surface convex with longitudinal row of large spine on midline; lower margin with large spine distally and few small spines medially; inner surface with few tubercles and sparse setae. Merus subtriangular in dorsal view; dorsodistal margin with strong spine; dorsal surface with rows of moderately small spines and tufts of long plumose setae; lateral face tuberculate, ventrolateral margin with row of large spines, distal spines strongest and accompanied by long setae; mesial face with sparse tubercles, ventromesial margin with row of moderately large spines, distal spines strongest and accompanied by plumose setae; ventral surface tuberculate. Ischium unarmed, but with sparse short setae on ventromesial margin.

Right cheliped ( Figs. 1D , 2A ) reaching proximal third of palm of left cheliped; narrow hiatus between dactyl and fixed finger. Dactyl longer than palm; upper margin with row small spines and numerous long setae; outer surface with scattered small spines and long setae; cutting edge with row of low, blunt, calcareous teeth, terminating in moderately large calcareous claw overlapped by fixed finger. Fixed finger with row of tubercles in midline partially obscured by long setae on outer surface; lower margin smooth but with sparse long setae; cutting edge with row of small calcareous teeth, terminating in moderately large calcareous claw. Palm with row of moderately large spines and tufts of long setae on upper margin; outer surface with longitudinal row of small spines in midline and with long setae. Carpus with row of large spines on upper margin; outer face with row of small spines in midline, lower half of surface with sparse tubercles, inner surface with setae distally. Merus triangular, dorsal margin with 1 large spine distally, and with numerous long, simple or plumose setae; ventrolateral margins with irregular row of small spines, ventromesial margin with few small spines. Ischium unarmed, but with few long setae.

P2 and P3 ( Fig. 2A ) slender. P2 ( Fig. 1E ) with dactyls 1.3 times as long as propodi, somewhat curved ventrally, but not twisted in dorsal view, terminating in moderately small corneous claws; dorsal and ventral margins each with mixture of short and long, plumose and simple setae; mesial surfaces each with row of setae in midline. Propodi 1.4 times as long as carpi, unarmed, each with sparse long and short setae on dorsal and ventral margins; mesial faces each with few setae. Carpi 0.7 times as long as meri; moderately large spine on dorsodistal and dorsoproximal and sparse, long setae; ventral margins unarmed. Meri each with sparse setae on dorsal and ventral margins, otherwise unarmed. Ischia unarmed, each with sparse setae. P3 ( Fig. 1F ) with dactyls and propodi same as in P2; carpi each with prominent dorsodistal spine, smaller spine on subdistal and subproximal dorsally, and sparse setae, lateral faces and ventral margins unarmed; meri and ischia also unarmed but with few setae. P4 semichelate ( Fig. 1G ); propodi with tiny dorsodistal spine, carpi with moderately large dorsodistal spine.

Telson ( Fig. 1H ) with distinct median cleft, long setae on terminal margin; left posterior lobe longer than right, left terminal margin with row of small spines, stronger spines extending onto lateral margin; right terminal margin also with row of small spines, but not extended onto lateral margin.

Colour in life. Shield cream with large dark brown spot medially, smaller dark brown patches anteriorly and laterally. Ocular peduncle generally white, greenish brown patch proximally, orangish red band on third distal, blue areas proximal to cornea, cornea light brown. Ocular acicle white with brown spot mesially. Antennular peduncles cream with dark brow ring on ultimate and penultimate segments distally. Antennal peduncles light brown, white band on fifth segment distally. Chelipeds cream, greenish brown on dactyl and fixed finger, palm with dark brown patches, spines white. P2 and P3 cream mottled with light brown, dark brown band on each propodi and carpi medially, meri with dark brown medially and subproximally ( Fig. 2A ).

Etymology: matabiru means blue eye in Bahasa Indonesia, alluding to the blue colour of ocular peduncles; use as a noun in apposition.

Remarks. Within the eight species of the D. pallescens group, four species have the antennular peduncle shorter than the ocular peduncle, namely, D. pallescens , D. biramus , D. viridis , and D. patae . Among these four species, D. matabiru most closely resembles D. pallescens in having strong spines on the shield and the left cheliped, the ocular peduncle as long as the shield, and P4 with distal spine on the dorsal margin of the carpi. However, the shield of the new species is clearly longer than broad ( Fig. 1A ) (as long as broad in D. pallescens ), the intercalary rostral process is very slender, reaching well beyond the tip of the longest spine of the ocular acicle ( Fig. 1A ) (larger at base to tapering at tip, as long as or only slightly reaching beyond the tip of the ocular acicle in D. pallescens ), the left cheliped with outer surface of fixed finger slightly convex, armed with strong spines, outer surface of the palm with row of strong spines on the midline and row of smaller spines between the midline and the upper margin ( Fig. 1C ), and the ventral margin of the merus of P2 unarmed ( Fig. 1E ) (outer surface of the fixed finger somewhat flattened, the palm with scattered tubercles or spines and with longitudinal row of strong spines beginning near the midpoint of proximal margin not reaching midlength, and the ventral margin of the merus of P2 with 1 to 5 spines in D. pallescens ) ( McLaughlin 2002: 91, figs.1–4).

Diogenes biramus and D. viridis differ in having the ocular peduncles much longer than the shield, the intercalary rostral process is short, triangular, reaching only midlength of the ocular acicle, and the terminal margin of the telson lacks the medial cleft ( Morgan 1987; Haig & Ball 1988) (the ocular peduncles as long as the shield, the intercalary rostral process is long, overreaching well beyond the ocular acicle, and the medial cleft of the telson is present in D. matabiru n. sp.). Diogenes patae is different in having dense setae on the chelipeds, P2 and P3 ( Asakura & Godwin 2006: fig. 2).

The life coloration will easily separate D. matabiru n. sp. from D. pallescens , D. biramus and D. viridis . The ocular peduncle of Diogenes matabiru is white, with greenish brown large patch proximally, orangish red broad band on third distal, and a blue area near cornea, the cheliped palm is cream with dark brown patches on dorsolateral and dorsomesial surface ( Fig. 2A ). In D. pallescens the ocular peduncle is white, light and dark brown patches on proximal half, brown band on distal third, the cheliped palm is cream with dark brown patches proximally on dorsal surface ( Fig. 2B ). In D. biramus the ocular peduncle is uniformly cream, the cheliped palm is light brown with pinkish brown patches on dorsolateral surface ( Fig. 2C ), while in D. viridis the ocular peduncle is uniformly light pink, the cheliped chela, palm, and carpus white, the merus green ( Fig. 2D ). The life colouration of D. patae is unknown.

Rahayu & Forest (1995) discussed the similarity between D. biramus and D. viridis , and suggested the possibility that the latter is a junior synonym of the former. The respective type localities of each species are not distant: D. biramus was described from Coral Bay, the Northern Territory, Australia, while D. viridis was from Maluku, Indonesia. However, examination of the specimens from Indonesia and Vanuatu revealed several characters that separate these two species. The most distinctive character is the colouration of P2 and P3. In D. biramus P2 and P3 cream, dactyl with light brown band medially, propodus with dark brown band medially and proximally, carpus and merus mottled with light brown, dark brown band medially ( Fig. 2C ). In D. viridis the dactyls of P2 and P3 are white, propodi, carpi and meri green with small white spots, white band distally ( Fig. 2D ). Morphological differences of these two species are also remarkable. Diogenes biramus has the following features: shield slightly longer than broad, left cheliped dactyl much longer than palm, fixed finger slightly flattened and lower margin with row of large spines that continued to lower margin of palm, propodus of P4 without any spine, telson subrectangular, broader than long. Diogenes viridis has the following features: shield as long as broad, left cheliped with dactyl as long as palm, fixed finger flattened, deflexed, lower margin with very small spines continued to lower margin of palm, P4 with distal spine on propodus, often also on carpus, telson longer than broad. The differences mentioned above confirmed the validity of these two species.

Habitat. The species was collected from muddy sandy substrate in mangrove environment, together with D. tumidus .

Figures

FIGURE 1. Diogenes matabiru n. sp., holotype, male, 2.7 mm (MZB Cru 5343). A, shield and cephalic appendages; B, chela, carpus and merus of left cheliped, dorsolateral view; C, chela, carpus and merus of right cheliped, dorsolateral view; D, left third maxilliped, mesial view; E, right P2, lateral view; F, left P3, lateral view; G, left P4, lateral view; H, telson. Setae partially omitted. Scale = 1 mm.

FIGURE 2. A. Diogenes matabiru n. sp., holotype, male, 2.7 mm (MZB Cru 5343); B, Diogenes pallescens Whitelegge, 1897, ovigerous female, 2.7 mm (MZB Cru 5347); C. Diogenes biramus Morgan, 1987, female, mm (ZRC 2021.0902); D, Diogenes viridis Haig & Ball, 1988 (Panglao, Philippines, 2004; specimen not collected).