Catapagurus cracens Komai, 2024, sp. nov.
Creators: name: Komai, Tomoyuki
Publisher: name: Zenodo
Year: 2024
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Decapoda
Paguridae
Catapagurus
Catapagurus cracens

description: Catapagurus cracens sp. nov.
(Figs. 1–5)
Material examined. Holotype. CBM-ZC 17835, male (sl 2.4 mm), off Hamahiga Island, Okinawa Islands, 150 m deep, 20 September 2017, baited trap, coll. K. Zensho.
Description. Gills biserial, 11 pairs.
Shield (Fig. 1A) approximately as long as broad; anterior margin between rostral lobe and lateral projections shallowly concave; anterolateral margins sloping, continuing to convex lateral margin; posterior margin roundly truncate; dorsal surface polished, with longitudinal rows short setae posterior to lateral projections; carapace lateral lobes moderately narrow, well calcified. Rostral lobe rounded, not reaching lateral projections. Lateral projections triangular, each with terminal, submarginal spine. Posterior carapace (Fig. 1B) 0.6 length of shield; posterolateral plates moderately wide anteriorly, drawn out into relatively thin bands reaching to posterior margins, posterior median plate weakly calcified.
Ocular peduncles (Fig. 1A) 0.7 times as long as shield, widened distally, slightly constricted proximal to base of corneas; corneal width 0.4 of peduncular length. Ocular acicles narrow, spike-like, reaching proximal 0.3 length of ocular peduncles, terminating acutely; widely separated basally. Interocular lobe clearly visible in dorsal view.
Antennular peduncle (Fig 1A, C) overreaching distal corneal margin by full length of ultimate article and 0.2 of penultimate article. Ultimate article half-length of shield, 4.4 times as long as distal height, with 2 moderately long setae at dorsolateral distal angle; dorsal surface with few minute setae. Penultimate article almost glabrous. Basal article ventrodistal margin terminating in spinule; statocyst lobe weakly inflated in proximal half of article, unarmed.
Antennal peduncle (Fig. 1A) overreaching distal corneal margin by half-length of fifth article. Fifth and fourth articles with few stiff setae. Third article unarmed on ventromesial distal angle, with sparse setae on mesial surface. Second article 2 with produced, spiniform dorsolateral distal angle falling far short of midlength of fourth article; dorsomesial distal angle with tiny spine. First article with spinule on lateral face; ventrodistal margin with 1 spinule. Antennal acicle moderately long, falling slightly short of distal end of fourth article and slightly overreaching corneal base, terminating in spine, otherwise unarmed. Flagellum elongate.
Third maxilliped (Fig. 1D, E) with endopod moderately slender; merus with small dorsodistal spine; ischium with crista dentata consisting of 8 small, equidistantly spaced teeth; accessory tooth small, subdistal in position. Exopod slightly overreaching distal end of carpus.
Right cheliped (Fig. 2A–D) not particularly elongate, relatively slender for genus. Chela elongate subovate in dorsal view, 3.4 times as long as wide. Dactylus 0.7 length of palm, with moderately long to long setae on every surface, terminating in calcareous claw; dorsal surface slightly convex transversely, without spines or tubercles; dorsomesial margin not delimited; mesial and ventral faces also smooth; occlusal margin with 1 small, sharp tooth proximally and 1 obtuse convexity with denticulate margin in distal to midlength, tip slightly overlapped by fixed finger. Palm 0.9 length of palm, 2.0 times as long as wide, surfaces almost smooth; dorsal surface gently convex, dorsomesial and dorsolateral margins not delimited; mesial face with sparse setae; ventral surface gently convex, with sparse setae; fixed finger terminating in sharp calcareous claw, with sparse tufts or individual setae on every surface, occlusal margin with low, broadly triangular calcareous tooth proximal to midlength, entire margin minutely denticulate. Carpus slightly shorter than merus, subcylindrical, 3.2 times as long as distal width; dorsomesial and dorsolateral margins each delimited with row of minute tubercles, strongest and acuminate distally, and with few short setae; dorsal surface with few granules; lateral surface almost smooth, ventromesial distal angle with 1 tiny spine; mesial surface with also smooth, ventromesial distal angle with minute tubercle; ventral surface gently convex, with few long setae. Merus subtriangular in cross section; dorsodistal margin with conspicuous spine; dorsal surface with few subdistal transverse ridges followed by row of evenly spaced setae; lateral surface with sparse setae, ventrolateral margin with 1 minute distal spine; mesial surface weakly granular ventrally, otherwise almost smooth, ventromesial margin with 1 triangular spine at distal angle; ventral surface finely granular, with few setae. Ischium with 1 small spine ventral surface laterally. Coxa (Fig. 1G) unarmed on ventromesial angle.
Left cheliped (Fig. 3A–C) slender, about 0.9 length of right cheliped. Chela 4.3 times as long as wide; fingers nearly straight in lateral view. Dactylus 1.2 times as long as palm, terminating in small corneous claw; surfaces smooth, with sparse tufts of setae; dorsomesial margin not delimited; occlusal margin with row of minute corneous teeth over almost entire length. Palm approximately 0.5 length of carpus, 2 times as long as wide; dorsomesial and dorsolateral margins not delimited, transversely convex dorsal surface smooth; ventral surface slightly convex, smooth; fixed finger with sparse tufts of setae, terminating in small corneous claw; occlusal margin with row of minute corneous teeth over entire length. Carpus subequal in length to merus; dorsomesial and dorsolateral margins delimited with row of granules (increasing in size and acuteness distally), dorsal surface smooth; lateral surface almost smooth except for few granules adjacent to dorsal margin, distoventral margin spineless; mesial and ventral surfaces also smooth, almost glabrous. Merus dorsodistal margin with 1 conspicuous spine; dorsal surface with 2 subdistal transverse ridges and row of setae; lateral surface smooth, faintly convex ventrolateral margin with 1 minute spine at distal angle; mesial surface almost smooth except for granulate adjacent to ventral part, faintly convex ventromesial margin with 1 small distal spine; ventral surface coarsely granulated. Ischium with 1 small subdistal spine on ventrolateral margin; ventral surface minutely granulated, with few short setae. Coxa (Fig. 1G) unarmed on ventromesial angle.
Second pereopods (Fig. 4A, B) slender, overreaching tips of outstretched chelipeds. Dactyli narrowly blade-shaped (length 11.8 of width), 1.3 times as long as propodi; in dorsal view, straight; in lateral view, slightly curved ventrally; dorsal margin with row of 19 (right) or 18 (left) moderately spaced, spiniform setae, increasing in length distally; mesial face concave, row of 17 (right) or 11 (left) minute spiniform setae adjacent to ventral margin; lateral surfaces with sparse short setae. Propodi 1.6 times as long as carpi; dorsal surfaces covered with minute granules; lateral and mesial surfaces with sparse minute granules; ventral margins without spiniform setae. Carpi short, about half-length of meri; dorsal surfaces minutely granulate, with 1 (right) or 3 (left) minute dorsodistal spines; otherwise almost smooth. Meri each with small dorsodistal spine and 2 subdistal spines (proximal spine located at distal 0.2), dorsal surface otherwise almost smooth, with row of evenly spaced moderately long setae; lateral and mesial surfaces smooth; ventral surfaces minutely granulate, glabrous, ventrolateral distal angle with tiny spine. Ischia unarmed.
Third pereopods (Fig. 4C, D) generally similar to second pereopods in general setation and armature, but somewhat longer. Dactyli narrowly blade-shaped (length 12.5 of width), 1.1 times as long as propodi; dorsal margins armed with row of 24 (left) or 26 (right) spiniform setae; mesial face concave, with row of 18 (left) or 20 (right) minute spiniform setae adjacent to ventral margin; lateral surfaces each with longitudinal row of setae along dorsal margin. Propodi tapering distally, 1.7 times as long as carpi; dorsal margins minutely granular; ventral margins each with 1 subdistal minute spiniform setae mesially. Carpi about half-length of meri; dorsal surfaces minutely granular, with trace of dorsodistal spine. Meri with small dorsodistal spine and 3 evenly spaced subdistal spines; ventrolateral distal margin with 1 tiny spine. Ischia longer than those of second pereopods, unarmed, ventral margins gently concave.
Fourth pereopods (Fig. 1G) weakly semichelate; dactyli each with well-developed preungual process extending well beyond tip of corneous claw; propodal rasp consisting of single row of corneous scales on distal 0.8 of ventral margin.
Fifth pereopods chelate. Right coxa with long sexual tube (Fig. 1I) curved dorsally over pleon and overreaching pleonal midline, terminus simple, glabrous. Left coxa (Fig. 1I) with papilla-like protrusion from gonopore partially surrounded by short setae.
Sixth thoracic sternite (Fig. 1H) anterior lobe broadly rounded, faintly bi-lobate, much shorter than large posterior lobe. Eighth sternite (fifth pereopods) (Fig. 1I) consisting of two small lobes separated by shallow median groove, each with small tubercle at posterolateral angle.
Pleon (Fig. 5) short, with small, uniramous unpaired left third and fourth pleopods, no fifth pleopod.
Uropodal protopods not protruding posteriorly.
Telson (Fig. 1J) with distinct lateral indentations; posterior lobes separated by moderately deep V-shaped median cleft, each terminating in subacute tip; lateral margins rounded, converging posteriorly; oblique terminal margins unarmed except for very short setae.
Colouration in life. Shield pale brown generally. Corneas light brown, ocular peduncles pale brown.Antennular peduncle ultimate article with 2 pale brown bands flanking whitish middle part; penultimate article with pale brown distal band and pink proximal blotch; basal article with short longitudinal stripes of brown laterally and mesially. Antennal peduncle generally translucent, with tinge of brown basally; fifth article with brown spots on lateral and mesial face subdistally; antennal acicle with subdistal brown ring; flagellum alternated with long brown band and short translucent ring. Chelipeds generally translucent with tinge of brown; no distinct longitudinal stripes. Ambulatory legs also generally translucent; carpi each with light brown spots on dorsal surface medially; meri with pale brown transverse band medially; no distinct longitudinal stripes on every article. Pleon translucent. See Fig. 5.
Genetic data. COI gene (LC822384), 16S rRNA gene (LC822236).
Distribution. Presently known only from off Hamahiga Island, Okinawa Islands, Ryukyu Islands, at a depth of 150 m.
Etymology. From the Latin word “ cracens ” (= slender), in reference to the relatively slender right cheliped of the new species.
Remarks. Catapagurus cracens sp. nov. appears closest to C. tenuilamina in having the weakly dilated cornea, the spike-like ocular acicle reaching the proximal one-third of the ocular peduncle, the moderately developed antennal acicle and narrow but blade-shaped dactyli of the second and third pereopods. Potential differentiating characters between the two species are: the ultimate article of the antennular peduncle is relatively stouter in C. cracens sp. nov. than in C. tenuilamina (4.4 times as long as the distal height versus 5.0 times as long; Fig. 1 versus Komai et al. 2022: fig. 1B); the chelipeds are slenderer and less granular in C. cracens sp. nov. than in C. tenuilamina (Figs. 2, 3 versus Komai et al. 2022: figs. 2, 3); coxae of the chelipeds are unarmed in C. cracens sp. nov., rather than being armed each with a small ventromesial distal spine in C. tenuilamina (Fig. 1F versus Komai et al. 2022: fig. 1E); propodi of the second and third pereopods are devoid of spiniform setae on the dorsal margin in C. cracens sp. nov. (Fig. 4A, C), whereas one to three spiniform setae are present in C. tenuilamina (cf. Komai et al. 2022: fig. 4A–D); the median cleft of the telson is V-shaped with oblique terminal margins in C. cracens (Fig. 1J), rather than U-shaped with longitudinal terminal margins in C. tenuilamina (Komai et al. 2022: fig. 1J). The living colouration is also substantially different between C. cracens sp. nov. and C. tenuilamina (cf. Fig. 5 and Komai et al. 2022: fig. 12A). In particular, in C. cracens sp. nov., there are no distinct markings on the second and third pereopods, whereas, in C. tenuilamina, the dactyli has a distinct reddish brown median stripes and small spots, and the propodi have three reddish brown longitudinal stripes on the lateral faces.
Of the 27 known species of Catapagurus, DNA sequence data is available only for C. tenuilamina (16S rRNA gene; LC664762), the morphologically closest relative to the present new species. The genetic divergence between the two taxa is 11.7%, well supporting distinctness of the new taxon from C. tenuilamina (e.g., Cabezas et al. 2009; Matzen da Silva et al. 2011; Lavery et al. 2014).
Fortunately, the status of the new species described in this study as distinct from the closely related species could be corroborated using genetic data. As suggested by McLaughlin et al. (2010), reassessment of diagnostic characters for species discrimination in Catapagurus would be necessary in the current situation. Due to insufficient genetic data, it is still difficult to improve the current situation. Accumulation of genetic data and reevaluation of diagnostic characters are much awaited for the genus.
description: Published as part of Komai, Tomoyuki, 2024, A new species of the hermit crab genus Catapagurus A. Milne-Edwards, 1880 (Decapoda: Anomura: Paguridae) from the Ryukyu Islands, Japan, pp. 573-583 in Zootaxa 5523 (5) on pages 574-581, DOI: 10.11646/zootaxa.5523.5.7, http://zenodo.org/record/13949992