Pagurus inflatus Komai, 2025, sp. nov.

Pagurus inflatus sp. nov. [New Japanese name: Udenaga-chigo-hon-yadokari] (Figs. 1–5) Material examined. Holotype: CBM-ZC 17882, male (sl 1.9 mm), TRV Toyoshio-maru, 2013-04 cruise, stn 10, Ohshima-shin-sone Bank, Amami Islands, Ryukyu Islands, Japan, 28°52.19'N, 129°32.70'E, 169–174 m, coral rock and sand with various sponges, 29 May 2013, dredge, coll. T. Komai, DNA voucher. Paratype: CBM-ZC 15876, 1 male (sl 1.8 mm), TRV Toyoshio-maru, 2017-03 cruise, stn 11, Ohshima-shin-sone Bank, Amami Islands, Ryukyu Islands, 28°52.98'N, 129°32.83'E, 165– 159 m, coral rock and sand with various sponges, 21 May 2017, dredge, coll. T. Komai. Description. Eleven pairs of biserial gills. Shield (Fig. 1A) 1.1 times longer than broad; dorsal surface smooth, gently convex, with few tufts of short setae, posterior to bases of ocular peduncles. Anterolateral margins sloping. Anterior margins between rostrum and lateral projections weakly concave. Posterior margin truncate. Rostrum obtusely subtriangular, terminating in blunt apex lacking spine. Lateral projections obtuse, with small submarginal spine. Posterior carapace generally membranous, posteromedian plate weekly sclerotised; branchiostegite almost glabrous on lateral surface. Ocular peduncle (Fig. 1A) moderately stout, about 0.7 length of shield (including cornea), slightly inflated basally, with row of tufts of setae, increasing in length distally, on dorsomesial face; corneas slightly dilated. Ocular acicles narrowly subtriangular, widely separated, with small sub-marginal spine. Antennular peduncle (Fig. 1A, B) overreaching distal corneal margin by 0.8 length of ultimate article s when fully extended. Ultimate article with 2 long setae at distolateral angle, and row of some short setae e on dorsal surface; penultimate and basal articles glabrous. Basal article with small process on dorsolateral distal margin and small spine on distal margin of statocyst lobe. Antennal peduncle (Fig. 1A) just reaching distal corneal margins. Fifth article with tuft of setae on lateral face distally. Fourth article almost glabrous. Third article also almost glabrous, unarmed on ventromesial distal angle. Second article with dorsolateral distal angle produced into acute projection not reaching midlength of fourth article, terminating in simple spine; dorsomesial distal angle with small spine. First article unarmed on lateral face or ventrodistal margin. Antennal acicle reaching to about midlength of fifth article, gently curved outward, terminating in acute spine with tufts of setae; mesial margin with row of setae. Flagellum broken off. Mouthparts not dissected. Third maxilliped (Fig. 1C, D) moderately slender. Ischium with well-developed crista dentata consisting of row of small subequal corneous teeth, and small accessory tooth. Merus and carpus unarmed. Right cheliped (Fig. 2) elongate; palm, fixed finger and dactylus slender, somewhat dorsoventrally compressed. Chela elongate oval, 2.4 times as long as broad, 1.3 times as long as carpus. Dactylus 0.7 length of palm; dorsomesial margin delimited with sharp, minutely denticulated ridge, dorsal surface slightly convex transversely, with few low, tiny tubercles; cutting edge with 4 blunt calcareous teeth over entire length, terminating in small corneous claw. Palm 1.4 times as long as broad, 0.8 length of carpus; dorsal surface slightly convex, unarmed, but with sparse long setae; dorsolateral margin delimited with toothed ridge (teeth larger around midlength of chela), dorsomesial margin also delimited with faintly crenulate ridge; occlusal margin of fixed finger with 2 blunt calcareous teeth in proximal half, row of small, low calcareous teeth in distal half, terminating in corneous claw; ventral surface gently convex, with scattered setae. Carpus longer than merus, slightly narrowing proximally in dorsal view, 2.3 times as long as distal breadth, strongly inflated and produced proximoventrally; dorsomesial margin not particularly delimited, armed with row of 1 minute + 3 small spines, dorsal surface sloping to lateral surface with scattered long setae, and laterally with 1 tiny spine; lateral surface almost glabrous with few setae, ventrolateral distal angle with 1 small spine; mesial surface with sparse setae, unarmed on ventromesial margin; ventral surface flat in anterior part, with sparse setae. Merus subtriangular; dorsal surface with sparse setae (distal setae bristle-like); lateral surface almost glabrous, ventrolateral margin with row of small spines in distal half; mesial surface almost glabrous except fir few subdistal bristles, ventromesial margin unarmed. Ischium unarmed on ventromesial margin; few short setae on dorsal and ventral surfaces. Left cheliped (Fig. 3) slender, not reaching much beyond proximal margin of palm of right cheliped. Chela 3.8 times as long as broad, 1.5 times as long as carpus. Dactylus and fixed finger nearly straight. Dactylus 1.1 length of palm, with sparse setae on surfaces; dorsal surface unarmed; occlusal margin with row of minute corneous teeth in distal half, terminating in small corneous claw. Palm 0.7 length of carpus; dorsal surface gently convex, unarmed, but with sparse short to moderately long setae; dorsomesial and dorsolateral margins not delimited; ventral surface gently convex, with scattered long setae; occlusal margin of fixed finger with row of very small calcareous teeth, terminating in small corneous claw. Carpus slightly longer than merus, slightly broadened distally, 3.0 times as long as distal breadth; dorsolateral margin with 3 small spines (including 1 spine on distal margin) in distal half, dorsomesial margin not delimited, unarmed; dorsodistal margin with 1 mesial spine; lateral surface with few setae, ventrolateral margin with 1 small distal spine; mesial surface also with few long setae, ventromesial margin unarmed; ventral surface gently convex, with scattered long setae. Merus subtriangular; dorsal surface with row of sparse setae; lateral surface almost glabrous with few setae, ventrolateral margin armed with 3 small spines and low, obtuse protuberances and sparse setae; mesial surface almost glabrous with few short setae dorsally, ventromesial margin unarmed; ventral surface with sparse tufts of long setae. Ischium unarmed, but with sparse setae on ventral surface. Ambulatory legs (Fig. 4) (left third pereopod missing in holotype), generally similar from left to right. Dactyli of second pereopods shorter than third, but both 1.0–1.1 times as long as propodi, 9.5–10.5 times as long as broad; dorsal margins each with sparse row of stiff setae, ventral margins each with row of 9–11 corneous spines, lateral faces unarmed, mesial faces each with row of corneous spinules dorsally, more numerous on third. Propodi about twice length of carpi; dorsal surfaces each with row of tufts of long setae; lateral and mesial surfaces glabrous; ventral margins each with 1 long corneous spine on distal margin and 1 smaller corneous spine somewhat distant from distal spine, and with row of short to long setae over entire length. Carpi each with trace of spine at dorsodistal margin (second) or no spine (third), row of long setae on dorsal surface. Meri dorsal and ventral margins with sparse long setae, ventrolateral distal margin with 1 small distal spine (second) or unarmed (third). Ischia unarmed but with short to long setae on ventral margins. Fourth pereopods (Fig. 1E) semichelate, sparsely setose, with prominent tuft of setae on dorsodistal margins of meri. Dactyli nearly straight, with preungual process. Propodal rasp consisting of a single row of corneous scales over 0.75 length of ventral margin. Fifth pereopods chelate. Coxae (Fig. 1G) each with gonopore, but without even papilla-like protrusion. Sixth thoracic sternite (Fig. 1F) with anterior lobe subtrapezoidal, with row of setae on anterior margin. Eighth thoracic (Fig. 1G) sternite with 2 rounded, non-setose lobes. Pleon (Fig. 5) dextrally twisted, with unpaired third to fifth pleopods. Telson (Fig. 1H, I) with faint transverse indentations; median cleft of posterior margin shallow; terminal margins slightly oblique, with some minute spinules, outermost spine directed outward [(in holotype (Fig. 1H), left posterior lobe seems to be once damaged]. Colouration in life. Carapace translucent, with scattered pale reddish brown dots; ocular peduncles, antennular peduncles and antennal peduncles generally translucent, also with scattered reddish brown dots, cornea yellowbrown; antennal flagella banded with brown and translucent; right cheliped generally whitish with scattered brown dots, dorsolateral margin of chela with brow spots, spines on carpus brown; left cheliped generally translucent with tinge of pale brow spines on carpus brown; second and third pereopods generally translucent, dactyli, propodi and carpi with interrupted brown stripe on dorsal margins, meri with scattered brown dots; pleon translucent (Fig. 5). Distribution. Known only from Ohshima-shin-sone Bank, off Amami-ohshima Island, at depths of 159– 174 m. Housing. Gastropod shells. No association with other invertebrates was seen. Etymology. The name refers to the noticeably inflated proximoventral face of the right cheliped carpus of the new species. Remarks. As mentioned above, based on the characters of the two available specimens, the present new taxon is assigned to the catch-all genus Pagurus. Pagurus inflatus sp. nov. is clearly distinguishable from all other species of Pagurus from the Indo-West Pacific region, except for P. lophochela Komai, 1999, by the elongate right cheliped with a flattened chela and a markedly inflated proximoventral surface of the carpus (Fig. 2A, B). I refrain from attempting to assign P. inflatus sp. nov. to any of the informal groups of Pagurus (cf. Forest & de Saint Laurent 1968; McLaughlin 1974) as it does not appear to match any of the currently diagnosed groups, and furthermore, it is widely acknowledged by colleagues that