Pagurixus icelus, Komai, 2010

Komai, Tomoyuki, 2010, New species and new records of the hermit crab genus Pagurixus Melin, 1939 (Crustacea: Decapoda: Anomura: Paguridae) from the Indo-West Pacific, Journal of Natural History 44 (21 - 22), pp. 1269-1342 : 1288-1294

Pagurixus icelus sp. nov.

( Figures 8–10 )

Material examined

Holotype. RAPA, stn 25, Anatakuri Naka Bay , Rapa, Austral Islands, French Polynesia, 27°38.4′S, 144°18.9′E, 3 m, block of dead coral, 13 November 2002, male SL 1.3 mm (MNHN-Pg 8302).

Paratypes. Austral Islands. RAPA, stn 16, 5 m, 9 November 2002, 3 males SL 1.1–1.4 mm, 1 ovigerous female SL 1.0 mm (MNHN-Na 8303); stn 17, SW of Rarapai Island, 27°34.6′S, 144°22.7′W, 9 m, under rock, 10 November 2002, 1 male SL 0.9 mm, 1 juvenile SL 0.7 mm (MNHN-Na 8304); same data as holotype, 3 males SL 1.0– 1.2 mm, 2 females SL 0.9, 1.1 mm, 1 ovigerous female SL 1.1mm (MNHN-Pg 8305); stn 29, N of Aturapa Island, 27°34.3′S, 144°21.0′W, subtidal, dead coral, 15 November 2002, 1 male SL 1.0 mm (MNHN-Pg 8306); stn 31, Point Mei, Rapa , 27°38.2′S, 144°18.2′W, 6 m, 16 November 2002, 1 ovigerous female SL 1.0 mm (MNHN-Na 8307); stn 38, Anatakuri Naka Bay, Rapa , 2 m, 22 November 2002, 2 males SL 1.0, 1.0 mm, 1 ovigerous female SL 1.1 mm (MNHN-Pg 8308) .

Description

Shield ( Figure 8A ) 1.1–1.2 times as long as broad; anterior margin between rostrum and lateral projections concave; anterolateral margins sloping; dorsal surface slightly convex, almost naked. Rostrum triangular, distinctly overreaching lateral projections, terminating acutely or subacutely. Lateral projections weakly produced, with or without marginal or submarginal spinule.

Ocular peduncles ( Figure 8A ) moderately stout, 0.5–0.6 length of shield, with few tufts of stiff setae on dorsal surface mesially; cornea not dilated, corneal width 0.3–0.4 of peduncular length; middle part very slightly inflated, wider than cornea. Ocular acicles subtriangular, usually each with submarginal spinule.

Antennular peduncles ( Figure 8A ) moderately stout, overreaching distal corneal margins by 0.3–0.5 lengths of ultimate segments. Ultimate segment with moderately short single seta on dorsolateral distal portion; ventral surface naked or only with few short setae ( Figure 7B ). Basal segment with small laterodistal spine on statocyst lobe. Ventral flagellum ( Figure 8B ) with row of sparse setae on lateral and mesial margins.

Antennal peduncles ( Figure 8A ) overreaching distal corneal margins by about 0.2 lengths of fifth segments. Third segment unarmed. Second segment with or without spinule at dorsomesial distal angle; laterodistal projection short, not reaching midlength of fourth segment, terminating in simple spine. First segment unarmed; ventromesial distal margin with small projection. Antennal acicle moderately long, arcuate, overreaching base, but not reaching distal margin of cornea; mesial margin with row of stiff setae. Antennal flagellum relatively short, 4.0–5.0 times longer than shield, each article with two or three short setae distally.

Male right cheliped ( Figure 9A–C ) massive, not particularly elongate. Chela 1.5–1.7 times longer than wide. Dactylus longer than palm, directed somewhat downward, terminating in calcareous claw; convex dorsal surface granular, dorsomesial margin not delimited; mesial face sparsely granular, ventral surface nearly smooth; cutting edge with one low, obtuse calcareous teeth on proximal half. Palm widened distally, subequal in length to carpus; dorsal surface convex, finely granular; dorsolateral margin not delimited on palm; dorsomesial margin sharply delimited with crenulate edge; lateral, mesial and ventral surfaces finely granular. Fixed finger somewhat curving downward, terminating in calcareous claw; lateral margin faintly delimited by row of granules; cutting edge with one obtuse calcareous tooth proximal to midlength. Carpus subequal in length to merus, length 1.0–1.1 times distal width, finely granular on surfaces; dorsal surface with few small tubercles and spiniform setae dorsomesially; sloping lateral surface lacking longitudinal ridge; ventral surface convex, without prominent setae on distal margin. Meral–carpal articulation lacking any pronounced clockwise rotation; dorsal surface of merus smooth, dorsodistal margin with few short setae; lateral face finely granular, ventrolateral margin unarmed; mesial face smooth, convex ventromesial margin unarmed; ventral surface smooth, with few long setae. Ischium with smooth ventromesial margin; surfaces smooth.

Female right cheliped ( Figure 10A–C ) appreciably larger than left. Chela about 1.4 times longer than broad, with markedly arched lateral margin in dorsal view. Dactylus longer than palm, terminating in small corneous claw; dorsal surface rounded, with scattered short setae; dorsomesial margin not clearly delimited, but with short ridges; mesial and ventral surfaces apparently smooth; cutting edge with row of small corneous teeth on distal 0.7–0.8. Palm distinctly shorter than carpus; slightly convex dorsal surface covered with sparse small granules; dorsolateral margin delimited by sharp, granular ridge extending to tip of fixed finger; dorsomesial margin also delimited by sharp, faintly granular ridge; lateral, mesial, and ventral surfaces all smooth; ventral surface with few short setae. Fixed finger terminating in small corneous claw; cutting edge with row of small corneous teeth in distal half. Carpus 1.2–1.3 times longer than broad and slightly longer than merus; dorsal surface with scattered small granules, dorsomesial part with some spinulose tubercles and spiniform setae, dorsodistal margin unarmed; lateral surface smooth, strongly convex ventrolateral margin granulate in distal half; mesial surface also smooth, ventrolateral margin unarmed; ventral surface strongly convex. Merus smooth on dorsal surface, unarmed on dorsodistal margin; lateral face apparently smooth, ventrolateral margin with row of small spines or spinulose tubercles; mesial face smooth, convex ventromesial margin unarmed or produced; ventral surface also smooth, only with few setae.

Left cheliped ( Figure 9D–F ) similar between male and female, moderately short and stout. Chela 2.4–2.7 times longer than wide, about 1.2 times longer than carpus. Dactylus longer than palm, terminating in small corneous claw, with sparse tufts of setae on surfaces; dorsal surface smooth; cutting edge with row of small corneous teeth. Palm about half length of carpus; dorsal surface convex, with two or three irregular longitudinal rows of small spinulose tubercles or granules medially; dorsolateral and dorsomesial margins not delimited; surfaces smooth or finely granular, with scattered short to long setae on ventral surface. Fixed finger terminating in small corneous claw, cutting edge with row of small corneous teeth. Carpus moderately slen- der, somewhat compressed laterally, subequal in length to merus; length 2.0–2.3 times distal width and 2.0–2.2 times height; dorsolateral margin unarmed or with few small spines and stiff setae, dorsomesial margin with row of three to five small spines in distal half and some spiniform setae; dorsodistal margin with some small spines; lateral face nearly perpendicular, smooth, ventrolateral margin granular; mesial face also nearly smooth, with long setae dorsally and distally; ventral surface convex, with few long setae. Merus smooth on dorsal surface, dorsodistal margin unarmed; lateral surface smooth, ventrolateral margin with row of tiny spines; mesial face also smooth, ventromesial margin unarmed; ventral surface weakly convex, smooth, with few long setae. Ischium unarmed.

Ambulatory legs ( Figures 8C, F ) moderately stout, similar on right and left. Dactyli 0.9–1.0 times as long as propodi, 5.5–6.0 times longer than wide, terminating in large corneous claws; dorsal surfaces with sparse short setae; lateral and mesial faces smooth ( Figure 8D, G ); ventral margins each with seven or eight moderately long corneous spines increasing in size distally. Propodi not tapering distally, 3.6–4.5 times longer than wide (males) or about 3.0 times (females); dorsal surfaces with sparse moderately short setae; lateral faces smooth; ventral margins each with row of seven to nine corneous spinules increasing in size distally, ventrodistal margins each with paired corneous spines. Carpi each with small dorsodistal spine, dorsal surfaces otherwise unarmed ( Figure 8E ); ventrodistal margin of third noticeably produced and bearing tuft of setae only in females. Meri with smooth dorsal and ventral margins each bearing sparse moderately long setae; lateral surfaces nearly smooth; ventrolateral distal margins unarmed.

Fourth pereopods ( Figure 8H, I ) subequal and similar in both male and female. Dactyli moderately broad, straight, each terminating in small corneous claw, with tuft of short setae distally. Propodi with few setae on dorsal margins; mesial faces nearly flat or slightly convex, with few short setae; propodal rasp of single row of corneous scales. Carpi without prominent tufts of setae on mesial face.

Coxae of fifth pereopods slightly unequal in male ( Figure 8K ); right coxa with prominent tuft of setae reaching to left coxa; no development of posteromesial protrusion; papilla-like protrusion of vas deferens absent. Left coxa with gonopore; no development of sexual tube or protrusion of vas deference seen. Female with unpaired left gonopore.

Anterior lobe of sixth thoracic sternite ( Figure 8J ) subrectangular, with row of short setae on anterior margin. Eighth thoracic sternite ( Figure 8K ) composed of two slightly unequal, closely set, rounded lobes; ventral surface of each lobe flattened.

Telson ( Figure 8L ) with terminal margins nearly horizontal, each bearing three or four spinules.

Colouration

In preservative. No markings seen on shield and cephalic appendages. Right cheliped generally cream, palm with reddish brown spot at proximomesial angle; tubercles on mesial part of carpus reddish-brown; merus with thin transverse band subdistally. Propodi of ambulatory legs white in distal 0.2, each with three brownish longitudinal stripes on lateral surface not extending to distal white part; carpi also with one brownish longitudinal stripe on lateral surface.

Size

Largest male SL 1.4 mm, largest female SL 1.1 mm, ovigerous females SL 1.0– 1.1 mm.

Distribution

Known only from the Austral Islands, French Polynesia, at depths of 2–9 m. Etymology

From the Greek ikelos meaning like or resembling, in reference to the similarities shared with other species of the Pagurixus anceps group, such as P. handrecki and P. fasciatus .

Remarks

Pagurixus icelus sp. nov. closely resembles P. handrecki Gunn and Morgan, 1992 and P. fasciatus in having a sharply delimited dorsomesial margin of the palm of the male right cheliped. In addition, these three species can have five or more small corneous spines on the ventral surface of each ambulatory propodus, although the number of spines is fairly variable. This new species is readily distinguished from P. handrecki by the ornamentation and armament of the right cheliped. The carpus of the right cheliped bears only a few tiny dorsomesial spines and spiniform setae in P. icelus , rather than having several moderately strong dorsomesial spines and dorsolateral spinulose tubercles (male) or moderately strong dorsolateral spines (female) in P. handrecki ; the female right chela has smooth or granular dorsolateral and dorsomesial margins in P. icelus , whereas those margins are substantially spinose in P. handrecki (cf. Gunn and Morgan 1992, figure 3c–e); the ventrolateral and ventromesial margins of the merus are unarmed in P. icelus , while armed with a row of spines in P. handrecki . Furthermore, the carpus of the left cheliped lacks dorsolateral spines in the new species, whereas such spines are present in P. handrecki . From P. fasciatus , the new species differs in the more stout ocular peduncles and the absence of dorsolateral spines on the carpus of the left cheliped. Furthermore, the coxa of the right fifth pereopod is devoid of a posteromesial protrusion in P. icelus , which is developed in P. fasciatus .

With regard to general colouration, P. icelus and P. handrecki are similar in having longitudinal stripes on the propodi of the ambulatory legs. Differences in colouration in life between the new species and P. handrecki could not be assessed because no information on living specimens was available for P. icelus . Pagurixus fasciatus differs from the two relatives in the distal three segments generally dark brown with white rings at the distal parts of the propodi and at the articulations between the propodi and carpi.

Figures

Figure 7. Pagurixus aurantiaca sp. nov. paratype, female (shield length 1.40 mm; CBM-ZC 9645). (A) Right chela and carpus, dorsal view; (B) right cheliped, mesial view; (C) right cheliped, lateral view; (D) left third pereopod, lateral view. Note: Scale bar, 0.5 mm.

Figure 8. Pagurixus icelus sp. nov. holotype, male (shield length 1.27 mm; MNHN-Pg 8302). (A) Shield and cephalic appendages, dorsal view; (B) ultimate segment and ventral flagellum of left antennule, ventromesial view; (C) right second pereopod, lateral view; (D) right second pereopod, dactylus, mesial view; (E) right second pereopod, carpus, mesial view; (F) left third pereopod, lateral view; (G) left third pereopod, dactylus, mesial view; (H) left fourth pereopod, lateral view; (I) right fourth pereopod, lateral view; (J) sixth thoracic sternite, ventral view; (K) coxae of fifth pereopods and eighth thoracic sternite, ventral view; (L) telson, dorsal view. Notes: Scale bars, (A, C, D, G) 0.5 mm; (B, H–L) 0.25 mm.

Figure 9. Pagurixus icelus sp. nov. holotype, male (shield length 1.27 mm; MNHN-Pg 8302). (A) Right chela and carpus, dorsal view; (B) right cheliped, mesial view; (C) right cheliped, lateral view; (D) left chela and carpus, dorsal view; (E) left cheliped, mesial view; (F) left cheliped, lateral view. Note: Scale bar, 0.5 mm.

Figure 10. Pagurixus icelus sp. nov. holotype, ovigerous female (shield length 1.05 mm; MNHN-Pg 8308). (A) Right chela and carpus, dorsal view; (B) right cheliped, mesial view; (C) right cheliped, lateral view; (D) left third pereopod, lateral view. Note: Scale bar, 0.5 mm.