Eutrichopagurus granulimanus, Komai & Rahayu & Fujita, 2021

Komai, Tomoyuki, Rahayu, Dwi Listyo & Fujita, Yoshihisa, 2021, Hermit crabs of the family Paguridae (Crustacea: Decapoda: Anomura) from Christmas and Cocos (Keeling) Islands, Indian Ocean Territory of Australia, with descriptions of three new species and reappraisal of the genus Kumepagurus Komai & Osawa, 2012, Raffles Bulletin of Zoology 69, pp. 378-402 : 379-384

Eutrichopagurus granulimanus , new species

( Figs. 1–3 )

Material examined. Holotype: QM W29558, male (sl 1.5 mm), CI-D17-2011, Thunderdome Cave , Christmas Island, 10°27.906′S, 105°36.465′E, 3–16.6 m, 30 March 2011.

Description. Eleven pairs of deeply quadriserial gills.

Shield ( Fig. 1A ) subtriangular in general outline, approximately as long as wide; anterior margin between rostrum and lateral projections gently concave; anterolateral margins sloping; posterior margin roundly truncate; dorsal surface slightly convex transversely, with 1 median and 3 lateral pairs of tufts of short setae. Rostrum triangular, terminating in acute tip, distinctly overreaching lateral projections. Lateral projections obtusely triangular, each with stout marginal spine. Posterior carapace ( Fig. 1B ) with lateral lobes very narrow. Cardiac sulci not discernible. Sulci cardiobranchiales extending to posterior carapace margin, converging posteriorly. Posteromedian and posterolateral plates poorly calcified; branchiostegites membranous, almost glabrous.

Ocular peduncle (including cornea) ( Fig. 1A ) stout, about half-length of shield, widest at about midlength; no setae on surfaces; cornea well developed, but not inflated, slightly narrower than peduncle. Ocular acicle subtriangular, not elongate, terminating acutely, reaching proximal 0.2 of ocular peduncle; dorsal surface flat. Interocular lobe separated from ocular acicles, overhung by rostrum, but partially visible in dorsal view; anterior surface slightly convex.

Antennular peduncle ( Fig. 1A, C ) rather stout, when fully extended, overreaching distal corneal margin by approximately full length of article 3. Article 3 2.8 times as long as high, 1.7 times as long as article 2, slightly widened distally, with prominent tuft of long setae (length subequal to that of ultimate segment) arising on dorsodistal margin, partially masking flagella in dorsal view. Article 1 with distolateral margin not markedly produced; statocyst lobe slightly inflated, with small spine on lateral face. Dorsal flagellum ( Fig. 1C ) longer than peduncular article 3, consisting of very short aesthetasc-bearing portion (7 articles) and long distal portion (7 articles, more than twice of aesthetasc-bearing portion); ventral flagellum ( Fig. 1C ) less than half of dorsal flagellum in length, peduncular segment, consisting of 6 articles.

Antennal peduncle ( Fig. 1A ) overreaching distal corneal margin by full length of article 5. Article 5 slightly flattened. Article 4 with few setae mesially. Article 3 unarmed on ventromesial distal margin. Article 2 dorsolateral distal angle produced, reaching midlength of fourth segment, terminating in simple spine; dorsomesial distal angle with small spine; mesial surface with few short setae. Article 1 unarmed on lateral face; ventromesial distal margin somewhat produced anteriorly, but without armature. Antennal acicle overreaching distal corneal margin by half-length and reaching midlength of peduncular article 5, terminating in small spine; dorsomesial margin with row of sparse setae. Antennal flagellum about 2.5 times of shield length, overreaching extended right cheliped; each article with few short setae on distal margin.

Mouthparts not dissected. Maxilliped 3 ( Fig. 1D ) moderately stout; carpus unarmed on dorsodistal margin; merus with small dorsodistal spine and ventral spine arising at midlength; ischium with crista dentata composed of minute, closely set corneous teeth and 1 accessory tooth ( Fig. 1E ); basisischium fusion incomplete; basis with few minute denticles on ventromesial margin; exopod reaching slightly beyond distal margin of merus.

Chelipeds unequal in length, dissimilar with right much more robust than left. Right cheliped ( Figs. 2A, B , 3A, B ) moderately stout, fairly large compared to body. Chela elongate suboval in dorsal view, 2.3 times as long as wide (greatest width at midlength of palm). Dactylus 0.4 length of palm, noticeably curved in dorsal view, weakly curved in mesial view, with scattered short setae on surfaces; dorsal surface with coarse granules laterally, smooth otherwise, dorsomesial margin not delimited; mesial face with few granules medially; occlusal margin with 2 obtuse calcareous teeth, terminating in small corneous claw. Palm elongate subovate in dorsal view, 1.6 times as long as wide, slightly longer than carpus, with very few short setae on surfaces; dorsomesial and dorsolateral margins not delimited, surfaces with covering of coarse granules, except for nearly smooth fixed finger; dorsal and ventral surfaces gently convex. Fixed finger with broad obtuse calcareous tooth in proximal half of occlusal margin, terminating on blunt calcareous claw. Carpus slightly widened distally in dorsal view, subequal in length to merus; dorsomesial and dorsolateral margins not delimited, dorsal surface with 2 small spines mesial to midline, and few minute tubercles or granules; lateral and mesial faces with covering of coarse granules and latter also with sparse setae; ventral surface nearly smooth, gently convex, with few long setae, ventrolateral and ventromesial margins spineless. Merus with very low, short transverse ridges and some short stiff setae on dorsal surface, dorsodistal margin unarmed; lateral surface with scattered granules in distal half, otherwise nearly smooth, ventrolateral margin with row of 4 small spines in distal half; mesial surface smooth, with several stiff setae ventrally, ventromesial margin with row of 4 small spines in distal half; ventral surface slightly convex, with few granules. Ischium with set of 3 spiniform setae on lateral surface; ventromesial margin unarmed. Coxa unarmed.

Left cheliped ( Figs. 2C, D , 3C, D ) moderately slender. Chela about 3.8 times longer than wide (greatest width at base of dactylus). Dactylus 1.5 times longer than palm, without conspicuous armature on surfaces, terminating in small corneous claw; dorsomesial margin not delimited; surfaces with sparse short setae; occlusal margin with row of minute corneous teeth (teeth in proximal 0.6 narrowly spaced, those in distal 0.4 contiguous). Palm about 1.6 times as long as carpus; dorsal surface gently convex, nearly smooth, with sparse short setae; no delineation of dorsolateral or dorsomesial margins; lateral and mesial faces with few inconspicuous granules; ventral surface gently convex, with few long setae. Fixed finger nearly straight, with scattered short setae on surfaces; occlusal margin bordered with thin corneous plate. Carpus about 0.85 length of merus, slightly widened distally in dorsal view, 2.9 times as long as distal width; dorsolateral and dorsomesial margins not delimited, dorsal surface devoid of conspicuous spines, but with few short to long, bristle-like setae laterally and mesially; lateral and mesial faces smooth, ventrodistal angles spineless; ventral surface slightly convex, with few long setae. Merus with double row of short, bristle-like setae on dorsal surface, dorsodistal margin unarmed, but also with short bristle-like setae; lateral surface with row of short, bristle-like setae adjacent to ventral margin, ventrolateral margin with row of 3 widely spaced small spines in distal half; mesial surface with longitudinal row of short bristle-like setae along midline and much longer bristle-like setae adjacent to ventral margin, ventromesial margin with 4 small, widely spaced spines; ventral surface also with short to long bristle-like setae. Ischium unarmed, with few setae; lateral face with 1 short spiniform seta at ventrolateral distal angle. Coxa unarmed.

Ambulatory legs ( Fig. 3E–H ) moderately long and slender. Dactyli 1.1 times as long as propodi, in dorsal view straight, in lateral slightly curved; dorsal margins each with double row of short setae; lateral and mesial faces almost glabrous; ventral margins each with 8 or 9 moderately long, slender corneous spines. Propodi distinctly longer than carpi, slightly narrowing distally; dorsal surfaces each with sparse setae; lateral and mesial faces glabrous; ventral margins each with 1 slender corneous spine at distal margin, followed by 2 or 3 widely separated, corneous spines becoming shorter proximally. Carpi unarmed on dorsal margins, almost glabrous; ventrodistal angle with conspicuous corneous spine. Meri each with widely spaced small corneous spines or spiniform setae on dorsal surface; lateral surfaces with few minute spiniform setae (second) or almost glabrous (third); ventral margin slightly sinuous, spineless, with few setae. Ischia unarmed, with sparse setae on dorsal and ventral margins.

Pereopod 4 ( Fig. 1F ) semichelate. Dactylus slightly curved. Propodus with rasp consisting of single row of corneous scales. Carpus with prominent tuft of setae at dorsodistal angle.

Pereopods 5 chelate. Coxae ( Fig. 1G ) asymmetrical; right coxa with long, filamentous sexual tube (about 4 times of coxal length) directed posterolaterally and with prominent tuft of setae at base of sexual tube; left coxa with very short sexual tube, directed mesially and tapering distally.

Thoracic sternite 6 anterior lobe ( Fig. 1H ) poorly defined, with transverse row of short setae. Thoracic sternite 8 ( Fig. 1G ) consisting of two contiguous lobes.

Pleon dextrally twisted. Male with 3 unpaired, unequally biramous left pleopods (third to fifth).

Uropods markedly asymmetrical; protopods unarmed.

Telson ( Fig. 1I ) with faint lateral indentations at anterior one-third; posterior lobes obtuse, terminal margins slightly oblique, left with 3 minute spines, right with few minute spines, posterolateral margins each with fringe of long setae.

Colouration in life. Not known.

Distribution. Presently known only from Christmas Island; found in marine cave, connected to anchialine environments; collected at depth between 3 and 16.6 m.

Remarks. Determination of the generic assignment of this new species is not easy, because only the male holotype is available for study. Among the genera characterised by the possession of 11 pairs of deeply quadriserial gills, the ischium of the maxilliped 3 having at least one accessory tooth and a well-developed crista dentata, and the possession of prominent right and short left sexual tubes, the new species appears close to Cestopagurus Bouvier, 1897 , for which both male and female characters have been well documented (cf. de Saint Laurent, 1968; Komai & Takeda, 2005; Komai & Poupin, 2012; Komai et al., 2014). However, the structure of the right sexual tube is considerably different between the new species and species of Cestopagurus . In the new species, the right sexual tube is directed posterolaterally and filamentous in shape. In contrast, in species of Cestopagurus , the right sexual tube is moderately slender and oriented toward the left across the ventral body surface, although the length is quite variable according to species. Consequently, the new species cannot be assigned to Cestopagurus satisfactorily. The other genus characterised by the possession of 11 pairs of quadriserial gills and the well-developed crista dentata and accessory tooth on the maxilliped 3 ischium is Eutrichopagurus Komai, 2015 , represented only by its type species, E. shirakawai Komai, 2015 . Unfortunately, no information on the male of E. shirakawai is available so far. Similarities between the new species and E. shirakawai are also seen in the triangle-shaped shield and the presence of a prominent tuft of setae on the article 3 of the antennular peduncle; those features are not seen in species of Cestopagurus . Thus, the new species is assigned to Eutrichopagurus , although only provisionally. Collection of a male specimen of E. shirakawai and a female specimen of the new species will fully clarify the problem of the generic assignment of the present new species.

Eutrichopagurus granulimanus , new species, differs markedly from E. shirakawai in many respects, outlined as follows: the eyes are less reduced in E. granulimanus , new species, than in E. shirakawai ( Fig. 1A versus Komai, 2015: fig. 1B); the ocular acicles are short, oval in shape in E. granulimanus , new species ( Fig. 1A ), while they are elongate, spike-like in E. shirakawai (cf. Komai, 2015: fig. 1B); the article 3 of the antennular peduncle has a prominent tuft of setae arising from the entire dorsodistal margin in E. granulimanus , new species ( Fig. 1A, C ), whereas there is a tuft of long setae at the distolateral angle of the article in E. shirakawai (cf. Komai, 2015: fig. 1B, D); the chela and carpus of the right cheliped is covered with coarse granules in E. granulimanus , new species ( Figs. 2A, B , 3A ), rather than being only sparsely granulate in E. shirakawai (cf. Komai, 2015: fig. 2); the carpus of the left cheliped is unarmed on the dorsolateral and dorsomesial margins in E. granulimanus , new species ( Figs. 2C, D , 3D ), rather than armed with some spines on the respective margins in E. shirakawai (cf. Komai, 2015: fig. 3A–C); surfaces of the dactyli and propodi are smooth in E. granulimanus , new species ( Fig. 3E, G ), while microscopically granulate in E. shirakawai (cf. Komai, 2015: fig. 4A, C); carpi of the pereopods 2 and 3 are each armed with one long spiniform seta at the ventrodistal angle in E. granulimanus , new species ( Fig. 3E, G ), whereas such a spiniform seta is absent in each carpus of those pereopods in E. shirakawai (cf. Komai, 2015: fig. 4A, C).

Etymology. The specific epithet refers to the coarsely granulated right palm, a combination of the Latin granulis (= granular) and manus (= palm). Used as a noun in apposition.

Figures

Fig. 1. Eutrichopagurus granulimanus, new species, holotype, male (sl 1.5 mm), QM W29558. A, shield and cephalic appendages, dorsal view; B, carapace, dorsal view (setae omitted); C, left antennule, ultimate peduncular article and flagella, lateral view; D, left maxilliped 3, lateral view (flagellum of exopod concealed); E, same, ischium and basis, ventral view; F, left pereopod 4, lateral view; G, coxae of pereopods 5 and thoracic sternite 8, ventral view; H, thoracic sternite 6, ventral view; I, telson, dorsal view.

Fig. 2. Eutrichopagurus granulimanus, new species, holotype, male (sl 1.5 mm), QM W29558. A, right cheliped, mesial view; B, same, lateral view; C, left cheliped, mesial view; D, same, lateral view.

Fig. 3. Eutrichopagurus granulimanus, new species, holotype, male (sl 1.5 mm), QM W29558. A, chela of right cheliped, dorsal view; B, carpus of right cheliped, dorsal view; C, chela of left cheliped, dorsal view; D, carpus of left cheliped, dorsal view; E, right pereopod 2, lateral view; F, same, dactylus, mesial view; G, left pereopod 3, lateral view; H, same, dactylus, mesial view.