Pylopaguropsis decora Komai, 2025, sp. nov.
Creators: name: Komai, Tomoyuki
Publisher: name: Zenodo
Year: 2025
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Decapoda
Paguridae
Pylopaguropsis
Pylopaguropsis decora

description: Pylopaguropsis decora sp. nov.
[New Japanese name: Suzaku-zebra-yadokari]
(Figs. 1–6)
Pylopaguropsis sp. –– Arima 2014: 177, unnumbered figs.–– Lemaitre 2017: 143 (table 1, list).
Material examined. Holotype. CBM-ZC 17880, male (sl 8.0 mm), off Ose-zaki, Numazu, Shizuoka Prefecture, 69 m deep, 14 February 2014, SCUVA diving, coll. H. Arima, DNA voucher.
Description. Thirteen pairs of biserial gills.
Shield (Fig. 1A) 1.1 times as long as broad; anterolateral margins sloping; anterior margin between rostrum and lateral projections weakly concave; posterior margin roundly truncate; dorsal surface smooth, with some tufts of short setae arranged symmetrically. Rostrum moderately broadly triangular, terminating isp. novinule, far overreaching lateral projections. Lateral projections obtusely triangular, each with small submarginal spine.
Ocular peduncles (Fig. 1A) relatively slender, 0.7 length of shield, slightly inflated proximally, with row of tufts of short setae on dorsal surface mesially; corneas not dilated, width 0.16 of peduncular length. Ocular acicles triangular, apices acute, well separated basally.
Antennular peduncle (Fig. 1A), when fully extended, overreaching distal corneal margin by about 0.3 length of ultimate peduncular article. Ultimate article almost parallel-sided in dorsal view, with subdistal tuft of short setae near dorsolateral distal angle. Penultimate article glabrous, much shorter than ultimate article. Basal article with small spine on dorsolateral margin of statocyst lobe; ventromesial distal angle terminating in subacute tooth, but not particularly produced.
Antennal peduncle (Fig. 1A), when fully extended, reaching distal corneal margin. Fifth and fourth articles with few scattered setae. Third article with small spine at ventromedial distal angle and few setae. Second article with dorsolateral distal angle strongly produced, well reaching beyond midlength of fourth article, terminating in bifid spine; dorsomesial distal angle with small spine. First article with 3 spinules on ventrodistal margin lateral to excretely pore. Acicle barely reaching base of cornea or midlength of fifth peduncular article, noticeably arcuate; terminating acutely, with row of individual or tufts of setae. Flagellum far overreaching tip of outstretched right cheliped by about 0.4 length; most articles each with several short and moderately long setae.
Third maxilliped (Fig. 1B, C) with moderately slender endopod. Carpus and merus unarmed. Ischium with well-developed crista dentata consisting of row of corneous-tipped spines increased in size proximally, and 1 strong accessory tooth with corneous tip. Basis with 3 corneous-tipped spines on mesial margin.
Right cheliped (Fig. 2A–E) massive, operculate, almost glabrous except for few sparse short setae. Dactylus very broad, dorsoventrally flattened, noticeably curved ventrally, set slightly obliquely to palm, terminating into small corneous clow; surfaces almost glabrous except for row of tufts of short setae adjacent to occlusal margin on ventral surface; dorsal surface with covering of granules; dorsomesial margin sharply delimited with row of closely-spaced small tubercles; ventral surface gently rounded transversely, with scattered granules; occlusal margin faintly sinuous, with broad obtuse tooth proximally and row of small blunt tooth theretofore. Palm broad, particularly distally (1.1 times as wide as long measured along mesial margin); dorsal surface slightly convex, glabrous, with scattered blunt granules extending onto fixed finger, but no cosp. novicuous spines or tubercles; dorsolateral margin distinctly delimited with irregular row of small tubercles or granules, extending onto fixed finger, faintly sinuous in dorsal view; dorsomesial margin rounded; mesial face generally rounded, with covering of small granules; ventral surface nearly smooth, slightly elevated into oblique ridge between base of dactylus and midpoint near proximal end; fixed finger broadly triangular, terminating in blunt tip bearing 2 closely set corneous spinules; ventral surface with row of tufts of short setae adjacent to occlusal margin; occlusal margin with 1 low, broad tooth at midlength and row of few small blunt tooth proximally. Carpus considerably broader distally (1.2 times as long as distal width); dorsodistal margin with row of small spines; dorsal surface transversely convex, with sparse granules and short transverse ridges laterally; dorsolateral margin not delimited; dorsomesial margin also not clearly delimited, but with few small spines distally; ventral surface convex, with row of small tubercles on mesial margin, smooth on lateral side. Merus triangular; dorsodistal margin unarmed; dorsal surface with short, low transverse ridges in distal half; lateral surface with sparse granules and rugosity particularly on dorsal side, ventrolateral margin with row of small tubercles or granules; mesial face generally smooth but with sparse granules near ventromesial margin, ventromesial margin somewhat produced, with row of moderately large spines and tubercles; ventral surface produced on lateral side, nearly smooth. Ischium unarmed.
Left cheliped (Fig. 3A–D) slender, reaching base of dactylus of outstretched right cheliped; propodal-carpal articulation twisted counterclockwise approximately 30°; dactylus and fixed finger bent downward. Chela 2.8 times as long as wide. Dactylus 1.1 length of palm, terminating in small corneous claw, with scattered tufts of setae; dorsal surface slightly rounded transversely. Palm nearly parallel-sided, 1.4 times as long as broad; dorsal surface with longitudinal rows of tiny spines or tubercles mesially, remaining dorsal surface to lateral surface with minute, scattered single or bifid granules; mesial face smooth, with sparse tufts of setae; ventral surface also smooth, weakly convex transversely; fixed finger with sparse tufts of setae; occlusal margin with row of minute, sharp denticles, terminating in 2 paired corneous claw. Carpus broadened distally in dorsal view, 2.6 times as long as distal breadth; dorsomesial margin with row of moderately strong spines; dorsal surface with longitudinal row of smaller spines mesial to midline, dorsolateral surface sloping to lateral surface without delineation of margin, with scattered, coarse granules or tiny tubercles, and also with sparse setae (setae numerous along dorsomesial margin); dorsodistal margin with few small spines laterally; mesial face nearly flat, with few tiny tubercles dorsally and low, setae-bearing low protuberances ventrally; ventral surface slightly convex. Merus lateral surface with scattered coarse granules, ventrolateral margin with row of strong spines on distal half, followed by irregular rows of tiny, spinulose tubercles; mesial face glabrous, ventromesial margin with row of small spines or tubercles on proximal half. Ischium with row of minute denticles on ventromesial margin distally, otherwise unarmed.
Second and left third pereopods generally similar, right third pereopod approximately 1.2 times longer than left. Second pereopods (Fig. 4A–C) with dactyli 1.2 length of propodi, 6.7 times as long as broad, gently curved ventrally in lateral view, almost straight in dorsal view; dorsal margins each with row of tufts of stiff setae, ventral margins with 10 (right) or 12 (left) corneous spines, terminating in large corneous claw; mesial surfaces each with row of 11 corneous spinules adjacent to dorsal margin and 1 (right) or 2 (left) additional corneous spinule adjacent to ventral margin; lateral surfaces each with shallow median sulcus extending from base to beyond midlength; mesial surfaces each with faint median sulcus limited to proximal part. Propodi slightly arcuate, with row of tufts of setae on dorsal margins; lateral and mesial faces almost glabrous; ventral margins with sparse short setae and corneous spinule on distal margin. Carpi each with small dorsodistal spine and 6 additional dorsal spinules, and sparse tufts of setae on dorsal margin. Meri each with row of tufts of setae on dorsal and ventral margins, ventrolateral distal margin with 1 tiny subdistal spine; lateral and mesial faces glabrous. Ischia unarmed, tufts of setae on dorsal and ventral margins.
Left third pereopod (Fig. 4D–F) with dactylus 1.5 length of propodus, 6.5 times as long as broad, slightly twisted in dorsal view, slightly curved in lateral view, terminating in large corneous claw; dorsal margin with row of tufts of setae; ventral margin with row of 14 corneous spines increasing in size distally; lateral face with shallow median sulcus in proximal half, mesial face with row of corneous spinules adjacent to dorsal margin and row of single or paired corneous spinules along midline. Propodus with 1 corneous spinule on ventrodistal margin, followed by 2 corneous spinules on ventral margin; dorsal margin with row of tufts of setae; lateral and mesial faces glabrous. Carpus with small dorsodistal spine and sparse setae on dorsal margin. Merus unarmed, with row of tufts of setae on dorsal and ventral margins; lateral and mesial faces glabrous. Ischium unarmed; sinuous dorsal margin with row of setae.
Right third pereopod (Figs. 4G, H, 5A, B) not appreciably broader than left in distal two articles. Dactylus 1.5 length of propodus, 6.8 times as long as broad, slightly twisted in dorsal view, slightly curved in lateral view; dorsolateral margin forming distinct carina bearing row of about 40 minute spinules, dorsal face with row of tufts of long setae; lateral face with 2 shallow longitudinal sulci, lower sulcus with row of tufts of short setae; mesial face transversely convex, with row of 11 corneous spinules adjacent to dorsal margin, and scattered corneous spinules below dorsal row; ventral margins with row of 17 corneous spines. Propodus slightly arcuate, with sharply carinate dorsolateral margin over entire length, bearing row of minute spinules; dorsal surface flat, with row of tufts of stiff setae; lateral surface with shallow sulcus on dorsal half; mesial surface transversely convex, almost glabrous; ventral margin with row of 8 corneous spinules, ventrodistal margin with 2 corneous spinules. Carpus with small dorsodistal spine, but dorsal surface otherwise unarmed, but with row of tufts of stiff setae; lateral surface with row of tufts of short setae along midline, mesial surface with few short setae. Merus unarmed, with tufts of setae on dorsal and ventral margins. Ischium unarmed.
Fourth pereopods (Fig. 1D) with no preungual process on dactylus apparent. Propodal rasp of 2 rows of corneous scales extending almost over entire length of ventral margin. Carpus without dorsodistal spine.
Fifth pereopods chelate. Coxae each with gonopore partially masked by short setae (Fig. 1F).
Third thoracic sternite unarmed. Sixth thoracic sternite (Fig. 1E) with poorly defined, obsolescent lobe bearing several setae arranged in transverse rows. Eighth thoracic sternite (Fig. 1F) vertically compressed, divided in 2 blunt lobes.
Pleon (Fig. 6) dextrally twisted, with unpaired third to fifth pleopods. Uropods markedly asymmetrical.
Telson (Fig. 1G) with deep transverse indentation; posterior lobes distinctly wider than anterior lobes, subtriangular, separated by shallow median cleft; terminal margins oblique, left with row of several spinules not extending to lateral angle (tip of left posterolateral angle strongly folded), right with row of some spinules extending to lateral angle; lateral margins unarmed.
Colouration in life. Carapace and pleon generally white, anterolateral margins of shield lined by crimson; anterior part of branchiostegite also crimson, with thin, white median stripe. Ocular peduncles and acicles crimson, former with white stripes on dorsal midline and mesial face. Antennular peduncle basal article crimson; penultimate and ultimate articles yellow; flagella yellowish translucent. Antennal peduncles generally crimson, fifth article with broad white stripe on dorsal surface; antennal acicle white; antennal flagellum crimson, whitish proximally. Right chela dactylus and fixed finger whitish, palm with tinge of pink dorsomesially; carpus pinkish; merus crimson with thin white stripe on dorsal surface. Left chela orange-red, with irregular median white stripe on palm dorsal surface; carpus and merus crimson, with white stripes on dorsal surface along dorsolateral margin and mesial surface. Ambulatory legs generally crimson; dactylus with white median stripe on each lateral and mesial faces; propodi, carpi and meri each with 2 white stripes on lateral and mesial faces. Fourth and fifth pereopods pale orange, meri of fourth pereopods darker. See Fig.
Genetic data. COI (LC833902), 16S rRNA (LC834108).
Distribution. Known only from the type locality (Ose-zaki) in Suruga Bay, central Japan, at a depth of 69 m.
Remarks. Pylopaguropsis decora sp. nov. is referred to the P. magnimanus species group by its markedly dissimilar third pereopods with distinctly sculptured dactylus and propodus, but appears unique in the group in having a row of spinules on the dorsolateral carinae of the dactylus and propodus of the right third pereopod (Figs. 4G, 5A, B). A similar condition is not known thus far for any other congeneric species in the P. magnimanus group (cf. McLaughlin & Haig 1989; Asakura 2000; Asakura & Paulay 2003; Rahayu & Komai 2013). In the presence of spines on the dorsal surface of the left cheliped palm (including dorsomesial spines) and of additional spines on the dorsal surface of the carpi of the second pereopods, P. decora sp. nov. is similar to P. magnimanus and P. atlantica. Differentiating characters between P. decora sp. nov. and P. magnimanus include the following: (1) the palm of the right cheliped is only granulated on the dorsomesial part in P. decora sp. nov. (Fig. 2A–C), rather thasp. novinose in P. magnimanus (cf. McLaughlin & Haig 1989: fig. 9a); (2) the carpus of the right cheliped is devoid of cosp. novicuous spines on the dorsolateral surface in P. decora sp. nov. (Fig. 2E), but in contrast, this surface is armed with cosp. novicuous spines in P. magnimanus (cf. McLaughlin & Haig 1989: fig. 7a); (3) dorsolateral and dorsomesial spines on the left cheliped carpus are more numerous in the new species than in P. magnimanus (Fig. 3A versus McLaughlin & Haig 1989: fig. 11a); (4) the propodus of the right third pereopod has a distinctly carinate dorsolateral margin and a shallow longitudinal sulcus just below the dorsolateral carina, in P. decora sp. nov. (Fig. 4G), whereas there is no such dorsolateral carina or lateral sulcus on that article in P. magnimanus (cf. McLaughlin & Haig 1989: fig. 3a). Pylopaguropsis atlantica is unique in the genus in having a prominently elevated dorsolateral margin of the carpus of the right cheliped (McLaughlin & Haig 1989: fig. 7).
The living colouration of P. decora sp. nov. (Fig. 6) is unique among the known congeneric species (cf. McLaughlin & Haig 1989; Asakura 2000, 2010; Komai & Osawa 2004; Osawa & Okuno 2007; Rahayu & Komai 2013; Arima 2014).
Etymology. From the Latin “ decorus ” (= beautiful), in reference to the beautiful living colour of this new species.
description: Published as part of Komai, Tomoyuki, 2025, Two new species of the pagurid hermit crab genus Pylopaguropsis Alcock, 1905 (Decapoda: Anomura) from Japan, pp. 315-334 in Zootaxa 5620 (2) on pages 316-323, DOI: 10.11646/zootaxa.5620.2.6, http://zenodo.org/record/15219627