Kumepagurus noelensis, 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 : 385-390

Kumepagurus noelensis , new species

( Figs. 4–7 )

Material examined. Holotype: QM W29559, male (sl 1.5 mm), CI-D12-2011, Thunderdome Cave , Christmas Island, 10°27.906′S, 105°36.465′E, 3–16.6 m, 28 March 2011.

Paratypes: CHRISTMAS ISLAND. ZRC 2021.0630 , 3 males (sl 1.2–1.3 mm), 2 females (sl 1.0, 1.1 mm), 3 ovigerous females (sl 1.1–1.3 mm), CI-D02-2010, Thunderdome Cave , 10°27.906′S, 105°36.465′E, 25 January 2010 ; QM W29560, 1 ovigerous female (sl 1.3 mm), same data ; QM W29561, 1 ovigerous female (sl 1.1 mm), CI-D09-2011, same cave, 27 March 2011 ; ZRC 2021.0631 , 2 males (sl 1.4, 1.4 mm), same data as holotype .

Description. Shield ( Fig. 4A ) 1.0–1.1 times as long as broad; anterior margins between rostrum and lateral projections concave; anterolateral margins sloping, posterior margin roundly truncate; dorsal surface almost glabrous. Rostrum triangular, terminating in tiny spine. Lateral projections triangular, not reaching level of rostral tip; each with small submarginal spine. Posterior carapace membranous; with pair of tufts of short setae at level of midlength; posteromedian plate moderately wide, with slightly convex lateral margins; sulci cardiobranchiales parallel, extending to midlength between cervical groove and posteromedian margin of carapace.

Ocular peduncle ( Fig. 4A ) 0.6–0.7 times as long as shield, moderately stout, not tapering distally or inflated basally, almost glabrous; cornea slightly dilated, corneal width about 0.4 times peduncular length. Ocular acicle narrowly triangular, directed forward, terminating in acute point. Interocular lobe small, partially visible in dorsal view.

Antennular peduncle ( Fig. 4A ), when fully extended, overreaching ocular peduncle by full length of ultimate article. Basal article with small spine on lateral margin located slightly distal to midlength; distolateral angle produced in small lobe. Ultimate article elongate, 0.8 times as long as shield, slightly broadened distally in lateral view, with few long setae dorsally; no tuft of setae at dorsolateral distal angle. Dorsal flagellum ( Fig. 4A ) with distal portion much longer than proximal, aesthetasc-bearing portion.

Antennal peduncle ( Fig. 4A ) overreaching distal corneal margin by half-length of article 5. Article 1 unarmed on lateral face, ventromesial distal margin produced, with bifid spinule just lateral to antennal gland opening. Article 2 with dorsolateral distal angle produced, not reaching midlength of article 4, terminating in simple spine; dorsomesial distal angle with small spine. Article 3 with 1 small spine on ventrodistal margin. Articles 4 and 5 with few short individual or tufts setae mesially, article 5 slightly longer than article 4. Antennal acicle overreaching distal corneal margin by about 0.2 own length, not reaching distal end of article 5, terminating in small spine, bearing tufts of moderately long to long setae. Antennal flagellum very long, each article with few short to long setae distally.

Maxilliped 3 ( Fig. 4B ) with endopod moderately long and slender; carpus unarmed; merus with small dorsodistal spine; ischium and basis incompletely fused; crista dentata on ischium consisting of row of about 10 evenly spaced, sharply pointed corneous teeth, accessory tooth absent; basis with 1 tiny denticle on mesial margin ( Fig. 4C ).

Male right cheliped ( Figs. 5A, B , 6A–C ) massive. Chela suboperculiform, subrectangular in general outline in dorsal view, about 1.8 times longer than wide; propodal-carpal articulation rotated clockwise about 20° from perpendicular. Dactylus subequal in length to palm, articulating obliquely, noticeably curved ventrally; dorsal surface nearly flat, with scattered short setae, dorsomesial margin sharply carinate, faintly granulate; ventral face slightly elevated along midline, almost glabrous; occlusal margin strongly sinuous, with obtuse tooth subdistally, terminating in minute corneous claw. Palm longer than carpus, widest at about midlength, 1.1 times as long as wide; dorsal surface slightly convex longitudinally and transversely in general, with few granules and few short setae; dorsolateral margin delimited by carina extending onto fixed finger, becoming obsolescent proximally on palm; dorsomesial margin slightly upturned, delimited proximally by distinct, faintly granulate carina; mesial surface sparsely granular, with some short setae adjacent to dorsal margin; ventral surfaces (including fixed finger) evenly convex, almost glabrous with sparse minute granules. Fixed finger slightly deflexed, broad at base, tapering to rounded tip bearing 2 minute, subterminal corneous claws; ventral surface sloping to occlusal margin; oblique occlusal margin with 1 prominent, rounded tooth accommodated into concavity on occlusal margin of dactylus, distal part further with few much smaller blunt calcareous teeth. Carpus longer than merus, noticeably widened distally; dorsal surface elevated and carinate in midline, with row of small spines, sloping lateral and mesial sides each with scattered granules (granules more numerous and fine on lateral side) and some setae adjacent to midline; lateral margin not delimited, mesial margin sharply delimited by spinulose carina; ventrolateral face smooth; ventromesial face almost glabrous, slightly concave, ventromesial margin weakly denticulated; ventral surface elevated transversely at middle, anterior half shallowly concave transversely, posterior part weakly calcified. Merus with slightly granulate dorsal margin, dorsodistal margin unarmed; lateral surface with minute granules, almost glabrous, ventrolateral margin with row of setae and with minute denticle at rounded distal angle; mesial surface almost glabrous except for few short stiff setae near dorsal margin, ventromesial margin strongly convex, with 2 small, subdistal spines and with stiff setae; ventral surface deeply excavated to accommodate ventral surface of carpus. Ischium unarmed, almost glabrous except for few short stiff setae. Coxa unarmed.

Female right cheliped generally similar to male right cheliped. Chela ( Fig. 6A ) 1.6 times as long as wide; granules on dorsomesial margin of dactylus and palm of right cheliped more pronounced than in males.

Left cheliped ( Figs. 5C, D , 6D, G ) moderately slender, reaching level of base of dactylus of right cheliped when stretched, without noticeable rotation from perpendicular between chela and carpus. Chela about 4.1 times longer than wide and 1.4 times longer than carpus. Fingers slightly curved ventrally, without hiatus between them; fixed finger with sparse setae on surfaces and 2 tiny corneous claws at tip ( Fig. 6E ), cutting edge with row of minute corneous teeth; dactylus 1.2–1.4 times longer than palm (distal part damaged in holotype), with sparse tufts of short to moderately long setae on surfaces, terminating in tiny corneous claw; dorsomesial margin not delimited; occlusal margin with row of closely set, minute corneous teeth at least in distal half. Palm 1.5 length of carpus; dorsal surface gently convex, with sparse granules laterally and sparse tufts of short to moderately long setae, without delineation of dorsolateral and dorsomesial margins; lateral, mesial, and ventral faces generally smooth, with scattered setae. Carpus widened distally, length about 3 times of distal width; dorsal surface sloping to lateral and mesial faces, with 2 tiny spines distomesially (1 spine near dorsodistal mesial angle) and tufts of short to long stiff setae; lateral face with sparse granules and few short setae; mesial face with short to long stiff setae dorsally; ventral surface slightly convex, with sparse short to long setae. Merus with row of widely spaced, short setae on dorsal surface, dorsodistal margin unarmed; lateral face with sparse granules, ventrolateral margin with 2–4 small spines in distal 0.4; mesial face smooth, with stiff setae ventrally, ventromesial margin with 1 distal spine, otherwise unarmed; ventral surface with sparse tufts of long setae. Ischium unarmed, with sparse short setae. Coxa unarmed.

Ambulatory legs ( Fig. 7A–D ) relatively slender, slightly overreaching tip of outstretched right cheliped. Dactyli 1.3–1.5 (second) or 1.6–1.7 (third) length of propodi, about 10.3–12.7 times longer than wide, slightly curved ventrally in lateral view, nearly straight in dorsal view, terminating in long, slender corneous claws; dorsal margins each with row of short setae; lateral faces smooth; mesial faces each with row of 7–9 corneous spinules and row of short setae adjacent to dorsal margin; ventral margins each with 7–12 slender corneous spines increasing in size distally. Propodi slightly curved ventrally, those of second longer than those of third; dorsal margins each with row of setae, lateral and mesial faces almost glabrous; ventral margins with few short setae, ventrodistal margins each armed with 1 slender corneous spine. Carpi with or without spinule at dorsodistal angle and with few setae on dorsal surface; lateral and mesial faces smooth. Meri unarmed, with sparse setae on dorsal and ventral surfaces; ventrolateral distal margins shallowly concave in distal 0.2. Ischia unarmed. Distinct concavity on ventral margin around articulation between merus and ischium in pereopods 2.

Pereopods 4 ( Fig. 4D ) simple. Dactyli each with row of minute corneous teeth on ventral margin; dorsal margin with few long setae. Propodi each with tuft of setae distally on dorsal margin; rasp consisting of single row of corneous scales increasing in size distally; carpus with tufts of setae in distal half of dorsal margin.

Coxae of male pereopods 5 ( Fig. 4E ) slightly dissimilar in shape, almost glabrous. Right sexual tube medium in length, oriented toward exterior then recurved over anterior part of pleon, extending beyond midline ( Fig. 4F ); distal part tapering distally; basal portion without covering of short setae. Left sexual tube short (about twice length of coxal length), directed posterolaterally, distinctly extending beyond posterior margin of coxa, somewhat flattened, tapering distally to subacute tip; some short setae present on dorsal side.

Anterior lobe of thoracic sternite 6 ( Fig. 4G ) subsemicircular, with row of setae on anterior margin, setae longest in medial portion. Thoracic sternite 8 ( Fig. 4E ) with 2 compressed lobes, each lobe bearing marginal setae.

Pleon dextrally twisted. Male with relatively long, unequally biramous pleopods 3–5; pleopod 4 longest, with elongate exopod. Female with pleopods 2–5, without paired pleopods 1.

Telson ( Fig. 4H ) with slightly asymmetrical posterior lobes separated by very small median cleft; terminal margins oblique, microscopically denticulate; transverse indentations weakly delimited, each with tuft of short setae.

Colouration in life. Not known.

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

Remarks. Kumepagurus noelensis , new species, is generally similar to the sole congeneric species, K. cavernicolus , but differentiating characters are seen in the relative length of the antennal acicle and the shape and ornamentation of the right chela. In K. noelensis , new species, the antennal acicle is subequal in length to the ocular peduncle ( Fig. 4A ), but it is elongate, being distinctly longer than the ocular peduncle in K. cavernicolus (cf. Komai & Osawa, 2012: fig. 1A). The right chela is less operculiform with a nearly straight to distally convex lateral margin in K. noelensis , new species ( Fig. 6A ), rather than distinctly sinuous in K. cavernicolus (cf. Komai & Osawa, 2012: fig. 3A, D); the dorsomesial margin of the palm is regularly carinate in K. noelensis , new species ( Figs. 5A , 6A ), whereas that margin is furnished with a short, distinct crest proximally in K. cavernicolus (cf. Komai & Osawa, 2012: fig. 3B); the ventral surface of the palm is smooth to slightly granular in K. noelensis , new species ( Fig. 6B ), while there are several blister-like tubercles on the ventral surface in K. cavernicolus (cf. Komai & Osawa, 2012: fig. 3D).

All specimens came from Thunderdome Cave, suggesting that the new species is restricted to cave environments.

Etymology. The name refers to Christmas Island, the type locality of the new species. ‘Noël’ is a French word meaning Christmas.

Figures

Fig. 4. Kumepagurus noelensis, new species, holotype, male (sl 1.5 mm), QM W29559. A, shield and cephalic appendages, dorsal view; B, right maxilliped 3, lateral view; C, same, ischium and basis, ventral view; D, left pereopod 4, lateral view; E, coxae of pereopods 5 and thoracic sternite 8, ventral view; F, dorsal extension of right sexual tube, anterior part of pleon and right pereopod 5 also shown; G, thoracic sternite 6, ventral view; H, telson, dorsal view.

Fig. 5. Kumepagurus noelensis, new species, holotype, male (sl 1.5 mm), QM W29559. A, right cheliped, mesial view; B, same, lateral view; C, left cheliped, mesial view; D, same, lateral view.

Fig. 6. Kumepagurus noelensis, new species. A–E, holotype, male (sl 1.5 mm), QM W29559; F, G, paratype, ovigerous female (sl 1.1 mm), ZRC 2021.0630. A, F, chela of right cheliped, dorsal view; B, same, ventral view; C, carpus of right cheliped, dorsal view; D, chela and carpus of left cheliped, dorsal view (setae omitted; distal part of dactylus damaged); E, distal part of fixed finger, ventral view, showing the presence of 2 corneous claws; G, left chela, dorsal view.

Fig. 7. Kumepagurus noelensis, new species, holotype, male (sl 1.5 mm), QM W29559. A, right pereopod 2, lateral view; B, same, dactylus, mesial view; C, left pereopod 3, lateral view; D, same, dactylus, mesial view.