Kumepagurus kaikata, Komai, 2020

Komai, Tomoyuki, 2020, A new species of pagurid hermit crab assigned to the genus Kumepagurus Komai & Osawa, 2012 (Decapoda: Anomura: Paguroidea) from the Kaikata Seamount Izu-Ogasawara Arc, Japan, Zootaxa 4858 (2), pp. 241-250 : 242-249

publication ID	https://doi.org/ 10.11646/zootaxa.4858.2.5
publication LSID	lsid:zoobank.org:pub:47DABA81-90D6-49FA-8F1C-89D367B04A4C
DOI	https://doi.org/10.5281/zenodo.4411770
persistent identifier	https://treatment.plazi.org/id/A7A19E3D-0BC6-45C3-9D84-EA120893D72B
taxon LSID	lsid:zoobank.org:act:A7A19E3D-0BC6-45C3-9D84-EA120893D72B
treatment provided by	Plazi
scientific name	Kumepagurus kaikata
status	sp. nov.

Treatment

Kumepagurus kaikata n. sp.

[New Japanese name: Kaikata-hirate-yadokari]

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

Material examined. Holotype: ovigerous female (sl 1.7 mm), RV “Tansei-maru”, KT09-2 cruise, stn KK 01-2(1), KM Peak, Kaikata Seamount, Izu-Ogasawara Arc, 26°40.00’N, 140°55.54’E, 172– 165 m, 16 March 2009, dredge, coll. T. Komai, CBM-ZC 16169. GoogleMaps

Paratypes: 1 male (sl 1.7 mm; damaged), 1 female (sl 1.1 mm), 2 ovigerous females (sl 1.4, 1.4 mm), same data as holotype, CBM-ZC 16170 GoogleMaps .

Description. Gill lamellae biserial; pleurobranchs absent on thoracomeres 5 and 6 (pereopods 2 and 3).

Shield ( Fig. 1A View FIGURE 1 ) 1.0–1.1 times as long as wide; anterior margins between rostrum and lateral projections gently concave; anterolateral margins sloping, posterior margin roundly truncate; dorsal surface almost glabrous but having few tufts of short setae laterally. Rostrum triangular, terminating in small spine. Lateral projections obtusely triangular, not reaching level of rostral tip; each with small submarginal spine. Posterior carapace ( Fig. 5 View FIGURE 5 ) membranous; with pair of tufts of short setae at level of midlength; posteromedian plate moderately wide, weakly calcified; sulci cardiobranchiales parallel, not reaching midlength between cervical groove and posteromedian margin of carapace.

Ocular peduncles ( Fig. 1A View FIGURE 1 ) about 0.6 times as long as shield, moderately stout, not tapering distally or inflated basally, each with few short setae dorsomesially; corneas slightly dilated, corneal width about 0.3 times peduncular length. Ocular acicles triangular, terminating in marginal spine. Interocular lobe small, exceeded by rostrum, but still visible in dorsal view.

Antennular peduncles ( Fig. 1A View FIGURE 1 ) moderately long, when fully extended, overreaching distal corneal margins by half-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 0.5–0.6 length of shield, slightly broadened distally in lateral view, with few short setae. Dorsal flagellum with distal portion much longer than proximal, aesthetasc-bearing portion.

Antennal peduncles ( Fig. 2A View FIGURE 2 ) moderately long, reaching slightly beyond distal corneal margins by article 5. Article 1 unarmed on lateral face, ventromesial distal margin produced, without spinule lateral to antennal gland opening. Article 2 with dorsolateral distal angle strongly produced, falling slightly short of distal margin of article 4, terminating in simple spine; dorsomesial distal angle with strong spine. Article 3 with 1 strong spine at ventrodistal margin. Articles 4 and 5 with few short setae mesially, article 4 shorter than article 5. Antennal acicle slightly arcuate, not reaching distal corneal margin, reaching midlength of peduncular article 5, terminating in small spine, bearing sparse setae dorsomesially. Antennal flagellum ( Fig. 5 View FIGURE 5 ) moderately long, each article with some short to long setae distally.

Maxilliped 3 ( Fig. 1B View FIGURE 1 ) with endopod moderately long and slender; carpus unarmed; merus with conspicuous dorsodistal spine; ischium and basis incompletely fused; crista dentata on ischium ( Fig. 1C View FIGURE 1 ) consisting of 1 minute tooth at distal angle and 3 prominent, acute teeth, all directed proximally, accessory tooth absent; basis with 1 minute spinule on mesial margin.

Right cheliped ( Fig. 2 View FIGURE 2 ) massive, operculiform in both male and female. Female chela ( Fig. 2 View FIGURE 2 A–C) subcircular in general outline, about 1.3 times as long as wide, gently curved ventrally, almost glabrous; propodal-carpal articulation rotated clockwise about 20° from perpendicular. Dactylus longer than palm, articulating obliquely; dorsal surface nearly flat, almost smooth, dorsomesial margin produced, forming sharp crest with faintly granulated margin; ventral face convex along midline, shallowly concave proximolaterally, almost smooth; cutting edge with shallow concavity distal to midlength, otherwise faintly uneven, terminating in minute corneous claw. Palm subequal in length to carpus, distinctly widened distally, approximately as wide as long; dorsal surface almost flat, but slightly upturned along dorsolateral margin, bearing few tiny tubercles proximally; dorsolateral margin sharply carinate over entire length (including fixed finger), spinulose on palm, smooth on fixed finger; mesial face nearly perpendicular, dorsodistal part visible in dorsal view, bearing scattered small tubercles, but otherwise smooth; lateral face smooth; ventral surface gently convex transversely, with some blunt tubercles medially. Fixed finger cutting edge with 3 broad, obtuse calcareous teeth (middle tooth strongest), terminating in calcareous claw. Carpus subequal in length to merus, shorter than palm, noticeably widened distally; dorsal surface elevated in midline, with row of small spines, sloping lateral and mesial sides with few short setae; lateral margin not delimited, distally with 1 small submarginal spine, mesial margin sharply delimited by row of small spines (this spine row gently concave in lateral view); ventrolateral and ventromesial surfaces smooth, almost glabrous; ventral surface with distal part somewhat produced in mesial side, with few small tubercles, proximal part strongly sloping, flat, not calcified. Merus dorsal surface smooth, without transverse ridges or setal tufts, dorsodistal margin armed with 1 small spine mesially; lateral face smooth, ventrolateral margin elevated, strongly sinuous in lateral view, with row of 3 small, slender spines in distal half; mesial face nearly flat, smooth; ventromesial margin crested, strongly convex in lateral view, with row of small spines decreasing in size and acuteness proximally; distal part of ventral surface forming distinct concavity to accommodate flexed carpus, non-calcified, whereas proximal part well calcified. Ischium unarmed. Coxa unarmed.

Male right chela ( Fig. 2E View FIGURE 2 ) generally similar to that of female, but chela slightly more elongate (about 1.7 times as long as wide). Crest of palm dorsolateral margin with row of small tubercles, rather than small spines

Left cheliped ( Fig. 3 View FIGURE 3 A–C) moderately slender, not reaching base of dactylus of right cheliped, with slight degree of counterclockwise rotation from perpendicular. Chela 2.9 times as long as wide and 1.2 times longer than carpus; dactylus and fixed finger only slightly curved ventrally, without hiatus. Dactylus subequal in length to palm, unarmed but with sparse tufts of short to moderately long setae, terminating in small corneous claw (Fig.); dorsomesial margin not delimited; cutting edge with row of closely set corneous teeth in distal 0.7. Palm 0.6 length of carpus; dorsal surface gently convex transversely, with sparse tufts of individual short to long setae and few low protuberances mesially, dorsomesial margin not delimited but with 4 spinules in proximal half, dorsolateral margin not delimited, unarmed; mesial and ventral faces generally smooth, with scattered setae. Fixed finger terminating in 2 acute corneous spines (Fig.); cutting edge with evenly spaced, minute calcareous teeth. Carpus slightly widened distally, length about 5 times of distal width; dorsal surface sloping to lateral face, having tufts of short to long setae and 1 small proximal spine, dorsomesial margin with row of small spines more widely spaced proximally, dorsolateral margin not delimited but with 2 small spines proximally; dorsodistal lateral angle with 1 moderately large spine; lateral and mesial faces smooth, with sparse short to long setae; mesial face with long stiff setae dorsally; ventral surface slightly convex, with sparse long setae. Merus dorsal surface with 2 subdistal spines and few setae proximally, dorsodistal margin unarmed; lateral surface glabrous, ventrolateral margin with row of 5 slender spines in distal half; mesial surface also glabrous, ventromesial margin with 2 widely spaced, unequal spines; ventral surface with scattered long setae. Ischium unarmed, with scattered short setae. Coxa unarmed.

Ambulatory legs ( Fig. 4A, C View FIGURE 4 ) moderately slender, right pereopod 2 not reaching tip of outstretched right cheliped. Dactyli ( Fig. 4B, D View FIGURE 4 ) about 1.1 (second) or 1.3 (third) length of propodi, 9–10 times longer than wide, slightly curved ventrally in lateral view, nearly straight in dorsal view, terminating in moderately long corneous claws; dorsal margins each with row of moderately long setae; lateral faces nearly flat or proximally with faint longitudinal sulcus; mesial faces each with row of 1–4 corneous spinules adjacent to dorsal margin in distal 0.4; ventral margins each with 8–10 slender corneous spines increasing in size distally (Fig.). Propodi slightly curved ventrally, those of second longer than those of third; dorsal surfaces each with sparse short and long setae; lateral and mesial faces smooth; ventral surfaces with sparse short setae, ventrodistal margins each armed with 1 slender corneous spine mesially. Carpi with or without spinule at dorsodistal angle and with few setae on dorsal surface; lateral and mesial faces smooth. Meri unarmed or armed with 2 small spines (third) on dorsal surfaces, with sparse setae on dorsal and ventral surfaces; ventrolateral distal margins with 1 small subdistal spine (second) or unarmed (third), ventral margins otherwise unarmed. Ischia unarmed. Distinct concavity on ventral margin around articulation between merus and ischium in pereopods 2.

Pereopods 4 ( Fig. 1D View FIGURE 1 ) simple. Dactyli distinctly shorter than propodi, with row of corneous teeth on ventral margin, terminating in small corneous claw; dorsal margin with prominent tuft of stiff setae. Propodi each with tuft of setae on dorsal margin; rasp consisting of single row of corneous scales increasing in size distally; carpus and merus with numerous long setae on dorsal margin.

Pereopods 5 semichelate.

Anterior lobe of thoracic sternite 6 ( Fig. 1E View FIGURE 1 ) subovate (wider than long), with row of setae on anterior margin, setae longest in medial portion.

Male right sexual tube ( Fig. 1F View FIGURE 1 ) of medium length, coiled, oriented posterolaterally, tapering distally; tip roundly truncate; basal portion with few setae. Left sexual tube ( Fig. 1F View FIGURE 1 ) short, but distinctly extending beyond posterior margin of coxa, somewhat flattened, directed posterolaterally, tapering distally to acute tip; few short setae present on dorsal side. Coxae of pereopods 5 ( Fig. 1I View FIGURE 1 ) subequal in size, left with sparse, long setae on anterior margin. Thoracic sternite 8 ( Fig. 1F View FIGURE 1 ) with 2 rounded, contiguous lobes, each lobe bearing short setae anteriorly.

Pleon dextrally twisted ( Fig. 5 View FIGURE 5 ), with unequally biramous pleopods 3–5 in male, pleopod 4 longest, with elongate exopod. Female with unequally biramous pleopods 2–5, no paired pleopod 1.

Telson ( Fig. 1G View FIGURE 1 ) with slightly asymmetrical posterior lobes separated by very small median cleft; terminal margins oblique, microscopically denticulate; transverse indentations shallow; posterolateral margin of anterior lobe each with prominent tuft of setae.

Colouration in life. Shield generally orange, with broad whitish longitudinal stripe on either side of midline; posterior carapace medially pale orange, laterally whitish; ocular peduncle with broad white transverse band medially, orange distally and proximally, cornea gray; antennular peduncle orange-red; antennal peduncle generally orange, with distal white band on article 2, flagellum semitranslucent; right cheliped generally orange, dorsomesial part of dactylus whitish, carpus with white tint dorsomesially; left cheliped also generally orange, tips of fingers whitish; dactyli, propodi and carpi of pereopods 2 and 3 orange along dorsal and ventral margins and whitish medially, meri each with white patches distally and proximally on orange background; pleon entirely semitranslucent ( Fig. 5 View FIGURE 5 ).

Size. Ovigerous females sl 1.4–1.7 mm.

Distribution. Known only from the type locality on Kaikata Seamount, at depths of 165– 172 m.

Housing. Gastropod shells: Cryptogemma sp. ( Turridae ; CBM-ZM 180028) and Clivipollia sp. ( Buccinidae ; CBM-ZM 180030).

Remarks. In spite of the difference in the gill formula noted above, the new species, Kumepagurus kaikata , agrees well with the type species of the genus, K. cavernicolus , in other generic features, summarised in the above generic diagnosis. In particular, the consistency in the lack of an accessory tooth on the maxilliped 3 ischium, the operculiform right chela, the presence of two distal corneous claws on the left chela fixed finger, the simple pereopods 4 and the development and structure of the sexual tubes are remarkable. Consequently, I am reluctant to establish a new genus based only on the difference in pleurobranch development. Although uniformity in gill formula is usual in most pagurid genera, Kumepagurus is now the only genus in which the presence or absence of pleurobranch gills on the thoracomere 5 and 6 (pereopods 2 and 3) is variable. With regard to arthrobranch development, on the other hand, intrageneric variation in the presence of absence of those gills on maxilliped 3 has been reported for Pagurus Fabricius, 1775 ( Komai & Osawa 2001; Siddiqui & Komai 2008) and Turleania McLaughlin, 1997 ( Osawa & Fujita 2008; Komai 2020).

In addition to the difference in the gill formula, Kumepagurus kaikata n. sp. is different from K. cavernicolus in many ways, as outlined below: (1) the antennular peduncle ultimate article is proportionately much shorter in K. kaikata n. sp. than in K. cavernicolus (0.5–0.6 times as long as shield versus 0.9 times as long; cf. Fig. 1A View FIGURE 1 versus Komai & Osawa 2012: fig. 1A); (2) the antennal peduncle and acicle is also proportionately shorter in K. kaikata n. sp. (the antennal peduncle only slightly overreaches the distal corneal margin and the antennal acicle does not reach it; Fig. 1A View FIGURE 1 ) than in K. cavernicolus (both antennal peduncle and acicle far overreach the distal corneal margin; Komai & Osawa 2012: fig. 1A); (3) the crista dentata of the maxilliped 3 consists of 3 prominent, proximally oriented teeth in K. kaikata n. sp. ( Fig. 1C View FIGURE 1 ), rather than a row of about 10 much smaller, mesially directed teeth in K. cavernicolus (cf. Komai & Osawa 2012: fig. 1F); (4) the dorsolateral margin of the right chela palm is drawn into a sharp, tuberculate or spinose keel in K. kaikata n. sp. ( Fig. 2A, C, E View FIGURE 2 ), whereas only faintly delimited in K. cavernicolus (cf. Komai & Osawa 2012: fig. 3C); (5) the dorsomesial margin of the cheliped palm is spinose or tuberculate in K. kaikata n. sp. ( Figs. 2A, B, E View FIGURE 2 ), whereas generally rounded with a short crest at the proximal angle in K. cavernicolus (cf. Komai & Osawa 2012: fig. 3B); (6) the ventral surface of the right chela is almost smooth except for some obtuse tubercles on the median part in K. kaikata n. sp. ( Fig. 2D View FIGURE 2 ), but there is a covering of granules or rounded tubercles on the distal and mesial parts of the ventral surface in K. cavernicolus (cf. Komai & Osawa 2012: fig. 3D); (7) the left cheliped carpus is armed with a row of conspicuous spines on dorsomesial margin, a strong dorsolateral distal spine, a few proximal spines on the dorsolateral margin and one mid-proximal spine in K. kaikata n. sp. ( Fig. 3 View FIGURE 3 A–C), but there are only a few spinules on the dorsomesial margin and one small dorsolateral distal spine in K. cavernicolus (cf. Komai & Osawa 2012: fig. 4A–C); (8) the left cheliped merus is armed with two subdistal spines on the dorsal margin in K. kaikata n. sp. ( Fig. 1B, C View FIGURE 1 ), rather than unarmed in K. cavernicolus (cf. Komai & Osawa 2012: fig. 4A–C); (9) the terminal margins of the telson are less oblique in K. kaikata n. sp. than in K. cavernicolus (cf. Fig. 1G View FIGURE 1 versus Komai & Osawa 2012: fig. 1K).

Differences are seen also in the living colouration between the two species. In K. kaikata n. sp., the shield is generally orange with a pattern of longitudinal stripes; the ocular peduncle has red distal and proximal bands and white median band; the pereopods 2 and 3 dactyli and propodi have longitudinal orange stripe on the dorsal and ventral margins, but lacking transverse patterns; the pleon is entirely colourless ( Fig. 5 View FIGURE 5 ). In contrast, in K. cavernicolus , the shield is generally white with a reddish median part; the ocular peduncle has a thin red lateral stripe but lacking transverse bands; the pereopods 2 and 3 dactyli are whitish distally and reddish proximally, and propodi are white distally and red proximally; the pleon is red ( Komai & Osawa 2012: fig. 6). Habitat is also very different between the two species. Specimens of K. kaikata n. sp. were dredged on rocky substrates at the sublittoral depths of 165–172 m on the top of a seamount, while the holotype of K. cavernicolus , only representative of the species, was collected from inside of marine cave at a depth of 38 m.

Etymology. Named after the Kaikata Seamount, where the new species was discovered. Used as a noun in apposition.