Pagurixus europa, 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 : 197-202

Pagurixus europa n. sp.

( Figs 4–6 )

Pagurixus sp. nov. 2. — 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 1.3 mm), MNHN-IU-2012-762.

Paratypes: same data as holotype, 3 males (sl 1.1–1.5 mm), 4 ovigerous females (sl 1.1–1.2 mm), MNHN-IU- 2012-763.

Non-type: same data as holotype, 1 juvenile (sl 0.9 mm), MNHN-IU-2012-764.

Description. Males. Shield ( Fig. 4 A) about 1.1 times longer than wide; anterior margin between rostrum and lateral projections slightly concave; anterolateral margins sloping; dorsal surface slightly convex, with few short setae laterally. Rostrum triangular, moderately produced, terminating acutely. Lateral projections obsolete, without submarginal spinule.

Ocular peduncle ( Fig. 4 A) moderately long and stout, about 0.6–0.7 length of shield, slightly inflated at midlength, with few tufts of short stiff setae on dorsal surface mesially; cornea slightly dilated, corneal diameter about 0.3 of peduncular length; basal part not inflated, as wide as cornea. Ocular acicle subtriangular, each with submarginal spinule.

Antennular peduncle ( Fig. 4 A) moderately stout, overreaching distal corneal margin by 0.2–0.3 length of ultimate segment. Ultimate segment about 2.0 times longer than high, with 1 or 2 short setae at dorsolateral distal portion; ventral surface without setal rows. Basal segment with small laterodistal spine on statocyst lobe. Ventral flagellum without row of dense long setae directed outwards on lateral and mesial margins.

Antennal peduncles ( Fig. 4 A) overreaching distal corneal margins by 0.3 length fifth segment. Third segment with small spine at ventromesial distal angle. Second segment with spinule at dorsomesial distal angle; laterodistal projection falling short of midlength of fourth segment, terminating in acute spine. First segment with or without laterodistal spinule; ventromesial distal margin with small projection. Antennal acicle moderately long, slightly arcuate, slightly overreaching base of cornea, terminating in spinule partially obscured by tuft of stiff setae; mesial margin with sparse stiff setae. Antennal flagellum somewhat overreaching extended right cheliped; each article with 1–3 very short setae (length less than one article) distally.

Male right cheliped ( Fig. 5 A–D) moderately stout to stout, not particularly elongate. Chela suboval, 1.8–2.0 times longer than wide. Dactylus about 0.8 length of palm measured along mesial margin, terminating in calcareous claw, slightly curved ventrally; dorsomesial or mesial margin not delimited; dorsal surface with sparse rounded granules; mesial surface with scattered row granules or low tubercles and sparse very short setae; ventral surface nearly smooth; cutting edge variable, bearing faint to distinct calcareous teeth, distal half occasionally with row of minute corneous teeth. Palm not widened distally, subequal in length to carpus; dorsal surface convex, microscopically granular, smooth to having several small, low tubercles, almost glabrous; dorsolateral margin faintly to slightly delimited; dorsomesial margin not particularly delimited, but with row of short oblique ridges; lateral and mesial faces almost glabrous; ventral surface also glabrous, gently convex. Fixed finger terminating in calcareous claw; cutting edge with row of 4 or 5 small, rounded or subtriangular calcareous teeth. Carpus subequal in length to merus, widened distally, length about 1.2 of distal width; dorsal surface almost smooth, mesially with 1 subdistal spine and low protuberances or oblique ridges each bearing 1–4 short to long bristle-like setae, and laterally with short bristle-like setae in proximal half; dorsodistal margin without conspicuous spines; lateral surface without trace of division, ventral lateral margin smooth; mesial surface smooth, ventromesial distal margin faintly tuberculate; ventral surface strongly convex. 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 distal margin minutely denticulate; ventromesial margin unarmed, bearing bristle-like stiff setae distally; ventral surface convex, with few long setae. Ischium with smooth ventromesial margin; surfaces smooth.

Left cheliped ( Fig. 5 E–G) moderately short, stout, distinctly shorter than right. Chela elongate subovate in dorsal view, about 2.7 times longer than wide, about 1.3 times longer than carpus. Dactylus longer than palm, terminating in small corneous claw, with tufts of stiff setae on dorsal and mesial surfaces; dorsal surface rounded, unarmed; cutting edge with row of small corneous teeth. Palm about half length of carpus; dorsal surface with low, tuberculate crest mesial to midline and double row of small tubercles along midline; dorsolateral and dorsomesial margins not delimited; lateral surface with sparse granules; mesial and ventral surfaces smooth; few long setae on ventral surface. Fixed finger terminating in corneous claw; cutting edge with row of small corneous teeth in distal half. Carpus somewhat compressed laterally, slightly shorter than merus; length 2.4 of distal width and 1.7 of height; dorsolateral margin with 2 small spines and few bristle-like setae, dorsomesial margin with 3 small spines and bristle-like stiff setae (proximal setae arranged in few short oblique rows); dorsodistal margin with 1 small spine flanked by spines in dorsolateral and dorsomesial rows; lateral surface nearly perpendicular, without trace of division, smooth ventrolateral margin unarmed; mesial surface nearly smooth, ventrodistal margin unarmed; ventral surface convex, with sparse long setae. Merus glabrous on dorsal surface, dorsodistal margin unarmed; lateral surface almost smooth, ventrolateral margin with 3 small spines in distal 0.2; mesial face also smooth, ventromesial margin without spines, but with several bristle-like stiff setae; ventral surface convex, smooth, with sparse setae. Ischium unarmed.

Ambulatory legs ( Fig. 4 B, D) moderately stout, similar on right and left. Dactyli ( Fig. 4 C, E) about 0.8–0.9 times as long as propodi, 5.1–5.2 times longer than wide, terminating in large corneous claws; dorsal surfaces with sparse short setae; lateral and mesial faces smooth; ventral margins each with 5–7 moderately long corneous spines increasing in size distally. Propodi not tapering distally, 4.0–4.5 times longer than wide; dorsal surfaces with sparse short setae; lateral and mesial faces smooth; ventral margins each with 2 or 3 minute corneous spinules, ventrodistal margins each with single or paired small corneous spines. Carpi each with small dorsodistal spine, dorsal surfaces otherwise unarmed, bearing few short stiff setae. Meri with few short setae on smooth dorsal and ventral margins; lateral surfaces smooth; ventrolateral distal margins each with one minute spine (second) or unarmed (third).

Fourth pereopods ( Fig. 4 F) similar from left to right. Dactylus moderately broad, straight, terminating in small corneous claw, with short setae subterminally. Propodus with tuft of setae on dorsal margin distally; 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 slightly unequal, dissimilar ( Fig. 4 H); right coxa with prominent tuft of setae reaching mesial margin of left coxa; no development of posteromesial protrusion apparent; papilla-like protrusion of vas deferens present. Left coxa with gonopore masked by tuft of short setae; no protrusion of vas deference seen.

Anterior lobe of sixth thoracic sternite ( Fig. 4 G) subsemicircular, with some short setae on anterior margin. Eighth thoracic sternite ( Fig. 4 H) composed of two unequal, contiguous rounded lobes; each lobe bearing few short setae anterolaterally.

Pleon without distinctive features. Telson ( Fig. 4 I) with terminal margins nearly horizontal to somewhat oblique, with 1–3 (left) and 3 or 4 (right) spinules; lateral plates of posterior lobes delimited.

Female. Chelipeds subequal in length. Right cheliped ( Fig. 6 A–C) relatively slender for genus. Chela subtriangular. Dactylus distinctly longer than palm, with scattered setae on surfaces; cutting edge with row of small corneous teeth. Palm with dorsal surface slightly convex, bearing longitudinal row of low, tiny tubercles mesial to midline and few low tubercles along midline; dorsolateral margin delimited by tuberculate ridge extending onto midlength of fixed finger: dorsomesial margin also delimited by interrupted, faintly tuberculate ridge; lateral and mesial faces smooth; ventral surface also smooth, gently convex. Fixed finger with row of small corneous teeth on distal half of cutting edge. Carpus slightly widened distally, 1.7–1.8 times longer than wide; dorsal surface mesially with 1 small distal spine and few low tubercles, laterally with irregular rows of short bristle-like setae; lateral surface smooth, ventrolateral margin unarmed; mesial surface with 2 oblique, low ridges each bearing some long, bristle-like setae, followed by few individual bristle-like setae; ventral surface convex, almost glabrous. Merus unarmed dorsally; ventrolateral margin with 2 small spines in distal 0.2; ventromesial margin unarmed.

Unpaired left gonopore present.

Coloration. In preservative. Color fairly faded away, but trace of 2 brown transverse bands, occasionally interrupted medially, on propodi of the ambulatory legs. Similar pattern of the coloration of the ambulatory legs is also seen in P. anceps , P. dissimilis Osawa & Komai, 2007 , P. nanus Komai & Takada, 2006 , and P. patiae Komai, 2006 (Komai 2006; Komai & Takada 2006; Osawa & Komai 2007).

Distribution. So far known only from Europa Island; intertidal.

Remarks. Pagurixus europa n. sp. is referred to the P. anceps species group by the lack of setal rows on the ventral surface of the ultimate segment of antennular peduncle. It appears closest to P. haigae , now recorded from Europa Island. Shared characters include: ocular peduncle moderately stout, exceeded by antennular and antennal peduncles; carpi of second pereopods only with dorsodistal spine, otherwise unarmed on dorsal surfaces; fourth pereopods subequal, left without prominent tuft of setae on dactylus; dactylus and palm of right chela without dorsomesial or mesial ridges; carpus of right cheliped at least with dorsodistal spine; and dactyli of ambulatory legs each with six or seven corneous spines on ventral margin. Nevertheless, this new species can be morphologically distinguished from P. h a i g a e by the following characters. The ocular peduncle is slightly inflated mesially at the midlength in P. e u rop a n. sp., but such an inflation is not seen in P. haigae . The carpi of the chelipeds bear several bristle-like setae arising from short oblique ridges or low protuberances on the dorsomesial surfaces in P. e u ro p a, whereas there are only a few stiff setae on the dorsomesial surface in P. haigae . Furthermore, there is only a dorsomesial distal spine on the carpus of the right cheliped in P. europa n. sp., but there are several dorsomesial spines on the carpus of the right cheliped in P. haigae . In females, the chelipeds are subequal in P. europa n. sp., rather than clearly unequal with the right larger in P. h ai g ae. The left palm bears low but distinct tubercles arranged in longitudinal rows on the dorsal surface in P. eu ro pa n. sp., but the dorsal surface of the left palm is only slightly granular in P. haigae . The color pattern of the ambulatory legs is also different between the two species. In P. haigae , there is a brown or dark brown longitudinal stripe on the midline of the lateral surface of each propodus, whereas no median stripe is seen on the segments in P. europa n. sp.

In the possession of long bristle-like setae on the dorsomesial surfaces of carpi of the chelipeds, Pagurixus nanus also resembles P. e u ro p a n. sp., but the possession of two small proximal spines on carpi of the second pereopods distinguishes P. nanus from the new species.

Etymology. Named after the type locality, Europa Island. Used as a noun in apposition.

Figures

FIGURE 4. Pagurixus europa n. sp., holotype, male (sl 1.3 mm), BIORECIE, stn 10, MNHN-IU- 2012 - 762. A, shield and cephalic appendages, dorsal view; B, right second pereopod, lateral view, showing color pattern; C, same, dactylus, mesial view; D, left third pereopod, lateralview; E, same, dactylus, mesial view; F, left fourth pereopod, lateral view; G, sixth thoracic sternite, ventral view; H, coxae of fifth pereopods and eighth thoracic sternite, ventral view; I, telson, dorsal view. Scale bars: 0.5 mm.

FIGURE 5. Pagurixus europa n. sp., holotype, male (sl 1.3 mm), BIORECIE, stn 10, MNHN-IU- 2012 - 762. A, right cheliped, mesial view; B, same, lateral view; C, same, chela, dorsal view; D, same, carpus, dorsal view; E, left cheliped, mesial view; E, same, lateral view; F, same, chela and carpus, dorsal view. Scale bar: 0.5 mm.

FIGURE 6. Pagurixus europa n. sp., paratype, ovigerous female (sl 1.1 mm), BIORECIE, stn 10, MNHN-IU- 2012 - 763. A, right cheliped, lateral view; B, same, mesial view; C, same, chela and carpus, dorsal view. Scale bar: 0.5 mm.