Pagurus inflatus, Komai, 2025

Komai, Tomoyuki, 2025, A new species of hermit crab provisionally assigned to the genus Pagurus Fabricius, 1775 (Crustacea: Anomura: Paguridae) from the Ryukyu Islands, Japan, Zootaxa 5647 (1), pp. 51-68 : 55-63

publication ID	https://doi.org/10.11646/zootaxa.5647.1.3
publication LSID	lsid:zoobank.org:pub:C3B278EA-B98F-4C94-8B00-78EDDB993886
persistent identifier	https://treatment.plazi.org/id/E87087B6-5B4F-A854-FF4E-FF15988C3FDE
treatment provided by	Plazi
scientific name	Pagurus inflatus
status	sp. nov.

Treatment

Pagurus inflatus sp. nov.

[New Japanese name: Udenaga-chigo-hon-yadokari]

( Figs. 1–5 View FIGURE 1 View FIGURE 2 View FIGURE 3 View FIGURE 4 View FIGURE 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. GoogleMaps

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 GoogleMaps .

Description. Eleven pairs of biserial gills. Shield ( Fig. 1A View FIGURE 1 ) 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 View FIGURE 1 ) 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 View FIGURE 1 ) 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 View FIGURE 1 ) 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 View FIGURE 1 ) 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 View FIGURE 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 View FIGURE 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 View FIGURE 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 View FIGURE 1 ) 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 View FIGURE 1 ) each with gonopore, but without even papilla-like protrusion.

Sixth thoracic sternite ( Fig. 1F View FIGURE 1 ) with anterior lobe subtrapezoidal, with row of setae on anterior margin. Eighth thoracic ( Fig. 1G View FIGURE 1 ) sternite with 2 rounded, non-setose lobes.

Pleon ( Fig. 5 View FIGURE 5 ) dextrally twisted, with unpaired third to fifth pleopods.

Telson ( Fig. 1H, I View FIGURE 1 ) 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 View FIGURE 1 ), 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 View FIGURE 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 View FIGURE 2 ). 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 Pagurus is a heterogeneous assemblage that contains several species without group assignment (e.g., McLaughlin & Konishi 1994; Komai 1999; Lima & Lemaitre 2016; Lemaitre et al. 2017). The present new species and P. lophochela represent small-sized species in the genus (cf. Lemaitre et al. 2017), not exceeding 2.0 mm in sl. Pagurus inflatus sp. nov. is readily distinguished from P. lophochela by the absence of a dorsomesial crest on the left cheliped palm ( Fig. 3A, C View FIGURE 3 ), which is diagnostic for P. lophochela (cf. Komai 1999: fig. 25A–C). Other differentiating characters are: the antennal peduncle reaches the distal corneal margin in P. inflatus sp. nov., rather than falling short of it in P. lophochela ( Fig. 1A View FIGURE 1 versus Komai 1999: fig. 23A); the right cheliped is more elongate with more dorsoventrally compressed chela in P. inflatus sp. nov. than in P. lophochela ( Fig. 2A, B View FIGURE 2 versus Komai 1999: fig. 24C, D); the dorsolateral margin of the right chela is coarsely denticulated in P. inflatus sp. nov. ( Fig. 2B, C, D View FIGURE 2 ), rather than finely spinulose in P. lophochela (cf. Komai 1999: fig. 24A, C, D); the carpus of the right cheliped is armed with a dorsomesial row of small spines in P. inflatus sp. nov. ( Fig. 2A, C, D View FIGURE 2 ), whereas the dorsomesial margin is sharply delimited by a spinulose ridge in P. lophochela (cf. Komai 1999: fig. 24B, C); the left palm is strikingly shortened in P. lophochela (cf. Komai 1999: fig. 25A, C), while normally developed in P. inflatus sp. nov. ( Fig. 3A, C View FIGURE 3 ); the meri of the second pereopods are spineless on the ventral margins in P. inflatus sp. nov. ( Fig. 4A View FIGURE 4 ), whereas armed with a few small spines in P. lophochela (cf. Komai 1999: fig. 26A).

In the general shape and structure of the right cheliped, this new species resembles superficially to species of Goreopagurus McLaughlin, 1988 , currently represented by four species, G. pearcei ( Wass, 1963) , G. garthi McLaughlin & Haig, 1995 , G. poorei Lemaitre & McLaughlin, 2003 and G. lemaitrei Nucci & Melo, 2007 , and Spathapagurus Lemaitre & Felder, 2011 , represented by three Americasp. novecies, S. collinae Lemaitre & Felder, 2011 , S. gladius ( Benedict, 1892) and S. longimanus ( Wass, 1963) . However, the male right cheliped of this new species does not show any notable expansion of the mesial and/or lateral surfaces, which is present in all four species of Goreopagurus , although to varying degrees ( McLaughlin 1988; McLaughlin & Haig 1995; Lemaitre & McLaughlin 2003; Nucci & Melo 2007). Furthermore, Goreopagurus is diagnosed by the presence of a paired first pleopods in females, but the female characteristics for P. inflatus sp. nov. remain to be clarified.

Spathapagurus View in CoL includes two species that had been assigned to Pagurus View in CoL ( Lemaitre & Felder 2011; Ayón-Parente et al. 2022). Diagnostic characters of Spathapagurus View in CoL include the presence of paired, short sexual tubes slightly protruding from gonopores and masked by long, forwardly directed setae ( Lemaitre & Felder 2011; Ayón-Parente et al. 2022), and this sets the new species apart from Spathapagurus View in CoL . Furthermore, the three species of Spathapagurus View in CoL are different from the present new species in the following particulars: shield broader than long (versus longer than broad); ocular peduncles stout with dilated corneas (versus slender with non-dilated corneas); propodus and carpus of second and third pereopods spinose on dorsal margins (versus unarmed except for dorsodistal spine on carpus); terminal margins of telson strongly armed (versus weakly armed) ( Lemaitre & Felder 2011; Ayón-Parente et al. 2022). It seems unlikely that P. inflatus sp. nov. is congeneric with the three species assigned to Spathapagurus View in CoL .

A BLAST search showed that the 16S rRNA gene sequence of this new species had a 91% identity with the sequence of Propagurus gaudichaudi (H. Milne Edwards, 1836) ( JX238502 View Materials ) with the highest similarity, and was not identical to any of the species of Paguridae View in CoL registered in GenBank.

The phylogenetic analysis based on the 16S rRNA gene data ( Fig. 6 View FIGURE 6 ) clearly indicates that the currently diagnosed Pagurus is not monophyletic. The newly described species, Pagurus inflatus sp. nov., was found to group with two species of Catapagurus , although this relationship lacks strong statistical support due to a low bootstrap value (60.6%). Notably, there are no shared diagnostic features between Pagurus inflatus sp. nov. and Catapagurus according to the current generic diagnosis ( McLaughlin 2004; Poore & Ahyong 2023). Additionally, the phylogenetic results do not support a close relationship between P. inflatus sp. nov. and Goreopagurus pearcei , the type species of the genus.