Pagurixus cavicarpus, 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 : 1294-1300

Pagurixus cavicarpus sp. nov.

( Figures 11–13 )

Material examined

Holotype. Point Faaupo , Moorea, Society Islands, French Polynesia, 0–2 m, under rocks, 21 October 2001, coll. G. Paulay, 1 ovigerous female SL 2.3 mm ( FMNH 1710 ).

Paratype. New Caledonia, coll. Y. Plessis, 1 female SL 1.9 mm (MNHN-Pg 1928) .

Description

Shield ( Figure 11A ) about 1.1 times as long as broad; anterior margin between rostrum and lateral projections weakly concave; anterolateral margins sloping; dorsal surface slightly convex, with few tufts of setae laterally; lateral margins moderately convex. Rostrum triangular, well produced, far overreaching lateral projections, terminating acutely. Lateral projections obsolete, each with minute submarginal spinule.

Ocular peduncles ( Figure 11A ) stout, about 0.7 length of shield, each with row of tufts of stiff setae on dorsal surface (setae at base of cornea not extending beyond distal corneal margin); corneas slightly dilated, corneal width about 0.5 of peduncular length; basal part very slightly inflated, but narrower than corneal width. Ocular acicles subtriangular, each with minute submarginal spinule concealed by distal projection.

Antennular peduncles ( Figure 11A ) overreaching distal corneal margins by about 0.3 length of ultimate segment. Ultimate segment with tufts of long setae on dorsolateral distal portion; ventral surface with two longitudinal rows of dense short setae (setae directed outward) ( Figure 11B ). Basal segment with minute laterodistal spinule on statocyst lobe. Ventral flagellum ( Figure 11B ) with dense long setae on lateral and mesial margins.

Antennal peduncles ( Figure 11A ) overreaching distal corneal margins by about 0.2 length of fifth segment. Third segment with small spine at ventromesial distal angle, practically obscured by tuft of stiff setae. Second segment unarmed at dorsomesial distal angle; laterodistal projection not reaching midlength of fourth segment, terminating in simple spine. First segment unarmed; ventromesial distal margin produced in rounded lobe. Antennal acicle moderately long, arcuate, overreaching base of cornea, but not reaching distal corneal margin, rather abruptly terminating in spinule; mesial margin with row of tufts of stiff setae. Flagellum moderately long, exceeding 4.0 length of shield; each article with short setae distally.

Right cheliped ( Figure 12A–E ) not particularly elongate, appreciably larger than left cheliped. Chela subovate in dorsal view, naked, 1.5 times longer than broad, with arcuate lateral and slightly convex mesial margins. Dactylus straight, distinctly shorter than palm, terminating in calcareous claw; dorsomesial margin weakly delimited; surfaces coarsely granular; cutting edge faintly dentate. Palm subequal in length to carpus; slightly convex dorsal surface coarsely granular, without conspicuous spines; dorsolateral margin delimited with granular ridge extending onto tip of fixed finger, dorsomesial margin not delimited; lateral, mesial and ventral surfaces also granular, ventral surface gently convex. Fixed finger straight, terminating in calcareous claw; cutting edge faintly dentate. Carpus longer than merus; very strongly produced ventrally, ventrolateral and ventromesial margins markedly expanded, thus width of carpus much greater than that of palm; dorsal surface convex, sloping to lateral and mesial faces, with scattered coarse granules often forming transverse rows and with short spiniform setae; lateral face coarsely granular; mesial face also granular along ventrodistal margin, shallowly depressed proximally; ventral surface forming deep concavity, margins upturned, sharply crested, accommodating flexed palm; proximal face nearly perpendicular, also forming concavity accommodating ventrodistal portion of merus when flexed. Merus with one low transverse ridge subdistally and few tufts of setae proximally on dorsal surface, dorsodistal margin with short stiff setae; lateral face almost smooth, ventrolateral margin unarmed; mesial face also smooth, with one distal spine on ventromesial margin; ventral surface shallow concave, with few short setae. Ischium unarmed.

Left cheliped ( Figure 13A–C ) moderately stout. Chela about 2.5 times longer than broad. Dactylus distinctly longer than palm, slightly curved ventrally, with sparse tufts of short setae on surfaces; cutting edge with row of small corneous teeth, terminating in small corneous claw. Palm about half length of carpus; dorsal surface weakly convex, sparsely granular, dorsolateral margin not delimited, dorsomesial margin delimited by weak, interrupted ridge; lateral face with sparse granules and short oblique ridges; mesial face smooth; ventral surface slightly convex, with sparse short setae. Fixed finger slightly curved ventrally, terminating in small corneous claw; cutting edge with row of small, corneous teeth over entire length. Carpus slightly shorter than chela or merus, becoming noticeably higher distally; length about 2.2 of distal width and about 1.7 of greatest height; dorsolateral margin with row of tiny tubercles and long spiniform setae, dorsomesial margin with row of some tiny tubercles distally, dorsodistal margin with one tiny tubercle; lateral face steeply sloping, coarsely granular, ventrolateral margin unarmed; mesial face coarsely granular dorsally, otherwise nearly smooth, ventromesial distal margin unarmed. Merus nearly smooth on dorsal surface, dorsodistal margin only with stiff setae; lateral face ornamented by minute, vertical granules, ventrolateral margin unarmed; mesial surface nearly smooth, with few short stiff setae ventrally, ventromesial margin unarmed; ventral surface weakly convex, with few long setae. Ischium unarmed.

Ambulatory legs ( Figure 13D, F ) moderately long and stout, generally similar from right to left. Dactyli ( Figure 13E, G ) 0.8–0.9 length of propodi, 4.1–4.3 times longer than wide, terminating in large corneous claws; dorsal surfaces with sparse short setae; lateral and mesial faces each with few tufts of short setae, mesial faces unarmed; ventral margins each with five relatively long corneous spines notably increasing in size distally. Propodi slightly tapering distally, about 3.2 times longer than wide; dorsal surfaces with sparse tufts of short to moderately long setae; lateral faces nearly smooth, naked (second) or with scattered tufts of very short setae (third); ventral margins each with row of three minute corneous spinules, ventrodistal margins each with paired corneous spinules. Carpi each with small dorsodistal spine; dorsal surface otherwise unarmed, with sparse setae; lateral faces smooth. Meri broad, strongly compressed laterally, each with sparse short setae on dorsal surface; lateral faces granular (second) or smooth (third); ventral margins each with row of minute granules and short setae, ventrolateral distal margins slightly concave, each with small subdistal spine (second) or unarmed (third).

Fourth pereopods ( Figure 11C ) subequal and similar. Dactyli nearly straight, terminating in very small corneous claws, each with tuft of short setae on dorsal margin distally. Propodi each with tuft of setae distally on dorsal margin; mesial faces flat; propodal rasp consisting of single row of large corneous scales. Carpi devoid of mesial tufts of setae.

Anterior lobe of sixth thoracic sternite ( Figure 11D ) roundly subrectangular, anterior margin with row of stiff setae. Eighth thoracic sternite composed of two subequal, narrowly separated, rounded lobes.

Female with paired gonopores.

Telson ( Figure 11E ) with terminal margins slightly oblique, each bearing several small spines; dorsal surface adjacent to terminal margins slightly elevated, well calcified.

Colouration

In life (based on colour slide taken by G. Paulay). Shield generally white, with broad, pale brown longitudinal stripe on either side of midline; posterior carapace also whitish. Ocular peduncles generally white; corneas gray. Antennular peduncles banded with white and pale brown. Antennal peduncles whitish; flagellum generally brown, with narrow white rings. Right cheliped generally white; carpus with light brown blotches on dorsal surface. Ambulatory legs generally white, with brown longitudinal stripes on propodi to meri; dactyli with two brown rings (one middle and one proximal); propodi each with two stripes visible in lateral view (one dorsal and one median); carpi each with one dorsal and one lateral median stripe.

Size

Largest and ovigerous female SL 2.3 mm.

Distribution

Known only from Moorea, French Polynesia, and New Caledonia; 0–2 m.

Etymology

Named after the deeply excavated ventral surface of the right cheliped.

Remarks

Although only two female specimens were available for study, the presence of two setal rows on the ventral surface of the ultimate segment of the antennular peduncle and the lateral and mesial fringes of setae on the ventral antennular flagellum clearly suggest that this new species is referred to Pagurixus , and to the Pagurixus boninensis group. The lack of a division of the lateral face of the left cheliped places P. cavicarpus in the subgroup A of the P. boninensis group (cf. Komai and Osawa 2006). However, the new species is quite distinctive in the unique structure of the right cheliped, which superficially resembles that of species of Elassochirus Benedict, 1892 , E. cavimanus (Miers, 1879) and E. gilli (Benedict, 1892) . In particular, the strongly expanded carpus with a deeply excavated distoventral surface, which permits strong flexion of the entire cheliped, is characteristic. Furthermore, the ventral spines of each dactylus of the ambulatory legs are fewer compared with those of other species of the P. boninensis group (five versus more than five).

Figures

Figure 11. Pagurixus cavicarpus sp. nov. holotype, ovigerous female (shield length 2.3 mm; FMNH 1710). (A) Shield and cephalic appendages, dorsal view; (B) ultimate segment and ventral flagellum of left antennule, ventral view; (C) left fourth pereopod, lateral view; (D) sixth thoracic sternite, ventral view; (E) telson, dorsal view. Notes: Scale bars, (A) 1 mm; (B–E) 0.5 mm.

Figure 12. Pagurixus cavicarpus sp. nov. holotype, ovigerous female (shield length 2.3 mm; FMNH 1710). (A) Right chela, dorsal view; (B) right cheliped, mesial view; (C) right cheliped, lateral view; (D) carpus of right cheliped, dorsal view; (E) carpus of right cheliped, ventral view. Note: Scale bar, 1 mm.

Figure 13. Pagurixus cavicarpus sp. nov. holotype, ovigerous female (shield length 2.3 mm; FMNH 1710). (A) Left chela and carpus, dorsal view; (B) left cheliped, mesial view; (C) left cheliped, lateral view; (D) right second pereopod, lateral view; (E) right second pereopod, dactylus, mesial view; (F) left third pereopod, lateral view; (G) left third pereopod, dactylus, mesial view. Notes: Scale bars, (A–C, E, G) 1 mm; (D, F) 0.5 mm.