Pagurixus annulus, Komai, Tomoyuki & Poupin, Joseph, 2013

Komai, Tomoyuki & Poupin, Joseph, 2013, Records of the hermit crab genus Pagurixus Melin, 1939 (Crustacea: Decapoda: Anomura: Paguridae) from Europa Island, western Indian Ocean, with descriptions of two new species, Zootaxa 3608 (3), pp. 191-203 : 192-197

Pagurixus annulus n. sp.

( Figs 1 B, 2, 3)

Pagurixus sp. nov. 1.—Poupin et al. in press b.

Material examined. Holotype: BIORECIE, stn 10, Europa Island, 22°33.644’S, 40°38.37’E, intertidal, reef flat and lagoon channel, 10 November 2011, coll. J. Poupin, N. Gravier-Bonnet & M. Zubia, male (sl 1.5 mm), MNHN-IU-2012-604.

Description. Shield ( Fig. 2 A) about 1.2 times longer than wide; anterior margin between rostrum and lateral projections slightly concave; anterolateral margins sloping; dorsal surface slightly convex, with few tufts of short setae laterally. Rostrum triangular, moderately produced, terminating acutely. Lateral projections obsolete, each with submarginal spinule.

Ocular peduncle ( Fig. 2 A) moderately long and stout, about 0.7 length of shield, with few tufts of short stiff setae on dorsal surface mesially; cornea not dilated, corneal diameter about 0.4 of peduncular length; basal part not inflated, as wide as cornea. Ocular acicle subtriangular, each with submarginal spinule.

Antennular peduncle ( Fig. 2 A) stout, reaching distal corneal margin by tip of ultimate segment. Ultimate segment ( Fig. 2 B) 2.0 times longer than high, with prominent tuft of long setae on dorsolateral distal portion; ventral surface with 2 rows of soft, comparatively long setae directed outward. Basal segment with small laterodistal spine on statocyst lobe. Ventral flagellum with row of dense long setae directed outwards on lateral and mesial margins ( Fig. 2 B).

Antennal peduncles ( Fig. 2 A) reaching distal corneal margins by tip of fifth segment. Third segment with small spine at ventromesial distal angle. Second segment with spinule at dorsomesial distal angle; laterodistal projection far falling short of midlength of fourth segment, terminating in subacute spine. First segment with laterodistal spinule; ventromesial distal margin with small projection. Antennal acicle moderately long, slightly arcuate, slightly falling short of base of cornea, terminating in spinule obscured by tuft of stiff setae; mesial and lateral margin with sparse stiff setae. Antennal flagellum not reaching extended right cheliped; each article with few short setae on distal margin.

Male right cheliped ( Fig. 3 A–C) moderately stout, not particularly elongate. Chela suboval, about 1.9 times longer than wide. Dactylus subequal in length to palm measured along mesial margin, terminating in small corneous claw; dorsomesial or mesial margin not delimited; slightly rounded dorsal surface without conspicuous spines or tubercles, mesial surface slightly granular, ventral surface nearly smooth; cutting edge with 2 obtuse calcareous tooth in proximal 0.4 and row of minute, corneous teeth in distal 0.6. Palm not widened distally, distinctly shorter than carpus; dorsal surface convex, slightly granular, no conspicuous spines, with scattered sparse very short setae; dorsolateral margin faintly delimited; dorsomesial margin not delimited; lateral and mesial faces almost glabrous; ventral surface also smooth, gently convex, with few short setae. Fixed finger terminating in corneous claw; cutting edge with row of 4 small, rounded or subtriangular teeth in proximal 0.8 and row of minute corneous teeth in distal 0.2. Carpus subequal in length to merus, widened distally, length about 1.6 of distal width; dorsal surface with sparse coarse granules and mesial row of long bristle-like setae, but without conspicuous spines; dorsodistal margin without conspicuous spines; lateral surface without trace of division; ventral surface convex, ventrolateral and ventromesial margins faintly granulate. Meral-carpal articulation lacking any pronounced clockwise rotation. Merus unarmed on dorsodistal margin, dorsal surface also unarmed and glabrous; lateral and mesial faces also smooth, glabrous; ventrolateral margin armed with row of 3 small spines in distal 0.3; ventromesial margin slightly tuberculate in distal 0.4; ventral surface slightly convex, with sparse long setae. Ischium with smooth ventromesial margin; surfaces smooth.

Left cheliped ( Fig. 3 D–F) moderately short, stout, distinctly shorter than right. Chela elongate subovate in shape, about 2.5 times longer than wide, about 1.2 times longer than carpus. Dactylus slightly longer than palm, terminating in small corneous claw, with tufts of stiff setae on mesial surface; dorsal surface rounded, smooth; cutting edge with row of small corneous teeth. Palm about half length of carpus; dorsal surface with sparse granules; dorsolateral and dorsomesial margins not delimited; lateral surface with sparse granules; mesial and ventral surfaces smooth; scattered long setae on ventral surface (including fixed finger). Fixed finger terminating in small corneous claw, cutting edge with row of small calcareous teeth and distal row of small corneous teeth distal to midlength. Carpus somewhat compressed laterally, slightly shorter than merus; length 2.3 of distal width and 2.0 of height; dorsolateral margin without conspicuous spines, dorsomesial margin with row of tiny tubercles and bristle-like stiff setae; dorsodistal margin without conspicuous spines; lateral surface nearly perpendicular, without trace of division, bearing sparse granules, ventrolateral margin minutely denticulate; mesial surface nearly smooth, ventrodistal margin unarmed; ventral surface convex, with sparse long setae. Merus glabrous on dorsal surface, dorsodistal margin unarmed; lateral almost smooth, ventrolateral margin with row of 3 small spines in distal 0.3; mesial face also smooth, ventromesial margin with row of minute tubercles; ventral surface slightly convex, smooth, with sparse setae. Ischium unarmed.

Ambulatory legs ( Fig. 2 C, E) relatively stout, similar on right and left. Dactyli ( Fig. 2 D, F) about 0.8 times as long as propodi, 4.2–4.4 times longer than wide, terminating in large corneous claws; dorsal surfaces with sparse short setae; lateral and mesial faces smooth; ventral margins each with 5 moderately long corneous spines increasing in size distally. Propodi not tapering distally, 3.2–3.4 times longer than wide; dorsal surfaces with sparse tufts of moderately long setae; lateral and mesial faces smooth; ventral margins each with 3–5 minute corneous spinules, ventrodistal margins each with single or paired small corneous spines. Carpi each with small dorsodistal spine, dorsal surfaces smooth, bearing tufts of stiff setae. Meri with sparse setae on smooth dorsal and ventral margins; lateral surfaces nearly smooth; ventrolateral distal margins each with one small spine (second) or unarmed (third).

Only left fourth pereopod preserved ( Fig. 2 G, H). Dactylus moderately broad, straight, terminating in small corneous claw, with tuft of short setae subterminally. Propodus with few setae on dorsal margin; mesial faces nearly flat or slightly convex, with few short setae, but without prominent tuft of setae; propodal rasp of single row of corneous scales. Carpus without prominent tuft of setae on mesial face.

Coxae of male fifth pereopods unequal ( Fig. 2 J); right coxa with prominent tuft of setae not reaching mesial margin of left coxa; no development of posteromesial protrusion apparent; papilla-like protrusion of vas deferens present. Left coxa with gonopore posteriorly encircled by short setae; no protrusion of vas deference seen.

Anterior lobe of sixth thoracic sternite ( Fig. 2 I) roundly subrectangular, with row of sparse short setae on anterior margin. Eighth thoracic sternite ( Fig. 2 J) composed of two subequal narrowly separated, rounded lobes; each lobe bearing few short setae laterally to anteriorly.

Pleon without distinctive features. Telson ( Fig. 2 K) with terminal margins nearly horizontal, with 2 (left) and 5 (right) spinules.

Coloration. In preservative. Shield white. Ocular peduncle white, without conspicuous markings; cornea darkly pigmented. Antennular peduncle generally white, ultimate segment with orange distal ring. Antennal peduncle generally white, only first segment orange. Chelipeds and ambulatory legs banded with white and orange. Right chela orange in palm, white in fingers; carpus white in distal half, orange in proximal half; merus with orange transverse band distal to midlength. Left cheliped showing similar pattern of markings to right cheliped. Ambulatory legs with dactyli bearing orange ring occupying proximal 0.3; propodi each with orange ring at about midlength (third); carpi each with orange ring crossing at midlength; meri each with orange ring distal to midlength. (See Figs 1 B, 2C).

Distribution. So far known only from Europa Island, Mozambique Strait, western Indian Ocean; intertidal.

Remarks. This new species is assigned to the subgroup B of the Pagurixus boninensis species group (cf. Komai & Osawa 2006) by having two setal rows on the ventral surface of the ultimate segment of the antennular peduncle and the lack of lateral ridge on the lateral surface of the carpus of either cheliped, and is very similar to P. pseliophorus Komai & Osawa, 2006 , known only from southwestern Japan, in both morphology and color pattern. Shared diagnostic characters include: antennular peduncle relatively short, not overreaching distal corneal margin; setae on ventral surface of ultimate segment of antennular peduncle arranged in single row, not clustered in tufts or short transverse rows; carpus of right cheliped without conspicuous dorsomesial spines; carpus of left cheliped without dorsolateral spines; dactyli of ambulatory legs short and stout, about 0.8 times as long as propodi and less than 4.5 times longer than wide; and ambulatory legs having distinct transverse bands. Pagurixus annulus n. sp. is distinguished from P. pseliophorus by the absence of conspicuous dorsomesial spines (except for one spine located at the dorsomesial distal angle) on the carpus of the left cheliped and the lack of a ventromesial protrusion of the right coxa of the male fifth pereopod. In P. pseliophorus , the carpus of the left cheliped bears a dorsomesial row of conspicuous spines; the coxa of the male fifth pereopod is provided with a distinct, collar-like ventromesial protrusion. Furthermore, the ocular peduncle seems to be stouter in P. annulus n. sp. than in P. pseliophorus (the corneal width is about 0.4 times in the new species versus 0.3 or less in P. pseliophorus ) (Komai & Osawa 2006).

Pagurixus brachydactylus Komai & Osawa, 2006 , known only from the Ogasawara (Bonin) Islands, Japan, is also similar to P. annulus n. sp. Nevertheless, the new species is distinguished from P. brachydactylus by the different pattern of the setation of the ventral surface of the ultimate segment of the antennular peduncle, the presence of bristle-like setae on the dorsomesial surface of the right cheliped carpus, and the lack of prominent setal tufts on the mesial face of the propodus and carpus of the left fourth pereopod. In P. brachydactylus , the setal row on the ventral surface of the ultimate segment of the antennular peduncle consists of mixture of longer setae clustered in tufts and interspersing shorter setae; the carpus of the right cheliped is devoid of bristle-like setae on the dorsomesial surface; the propodus and carpus of the fourth pereopod bear prominent tuft setae respectively (Komai & Osawa 2006). In addition, the shield may be proportionally narrower in P. annulus n. sp. than in P. brachydactylus (1.2 times longer than wide versus 1.0–1.1 times as wide as long). The color pattern of the ambulatory legs is also similar between these two species, but the dactyli have a proximal ring in P. a n nu lu s, whereas they have short proximal longitudinal stripes in P. brachydactylus (cf. Komai & Osawa 2006: fig. 45C).

Etymology. From the Latin annulus , meaning ring, in reference to the color pattern of the ambulatory legs. Used as a noun in apposition.

Figures

FIGURE 2. Pagurixus annulus n. sp., holotype, male (sl 1.5 mm), BIORECIE, stn 10, MNHN-IU- 2012 - 604. A, shield and cephalic appendages, dorsal view; B, ultimate segment and flagella of right antennular peduncle, lateral view; C, right second pereopod, lateral view, showing color pattern; D, same, dactylus, mesial view; E, left third pereopod, lateral view; F, same, dactylus, mesial view; G, left fourth pereopod, lateral view; H, same, distal three segments, mesial view; I, sixth thoracic sternite, ventral view; J, coxae of fifth pereopods and eighth thoracic sternite, ventral view; K, telson, dorsal view. Scale bars: 0.5 mm.

FIGURE 3. Pagurixus annulus n. sp., holotype, male (sl 1.5 mm), BIORECIE, stn 10, MNHN-IU- 2012 - 604. A, right cheliped, mesial view; B, same, lateral view; C, same, chela and carpus, dorsal view; D, left cheliped, mesial view; E, same, lateral view; F, same, chela and carpus, dorsal view. Scale bar: 0.5 mm.

FIGURE 1. A, Pagurixus haigae Komai & Osawa, 2006, 1 male (sl 1.6 mm), 2 ovigerous females (sl 1.5, 1.6 mm), BIORECIE, stn 1, MNHN-IU- 2012 - 603; B, Pagurixus annulus n. sp., holotype, male (sl 1.5 mm), BIORECIE, stn 10, MNHN- IU- 2012 - 604, showing color pattern in preservative.