Oncopagurus pollicis, Lemaitre, 2014

Lemaitre, Rafael, 2014, A worldwide taxonomic and distributional synthesis of the genus Oncopagurus Lemaitre, 1996 (Crustacea: Decapoda: Anomura: Parapaguridae), with descriptions of nine new species, Raffles Bulletin of Zoology 62, pp. 210-301 : 273-277

Oncopagurus pollicis , new species

Figs. 35–37 , 51

Type material. Holotype, New Caledonia, CHALCAL 2, sta DW 72, 24°54.50'S, 168°22.30'E, 527 m, 28 October 1986: 1 M 3.2 mm (MNHN-IU-5496).

Description of holotype. Gills biserial. Shield ( Fig. 35A ) slightly longer than broad; dorsal surface weakly calcified medially, with scattered short setae; rostrum broadly rounded, weakly produced, with short mid-dorsal ridge; anterior margins weakly concave; lateral projections bluntly subtriangular; anterolateral margins sloping; posterior margin broadly rounded; ventrolateral margins of shield with slender spine on left side. Anterodistal margin of branchiostegite rounded, unarmed, setose.

Ocular peduncles ( Fig. 35A ) more than half length of shield; with longitudinal row of long setae dorsally; lateral and ventral faces weakly calcified. Cornea weakly dilated. Ocular acicles subtriangular, each terminating in strong spine; separated basally by about basal width of 1 acicle.

Antennular peduncle ( Fig. 35A ) exceeding distal margin of cornea by 0.7 to nearly full length or ultimate segment. Ultimate segment slightly less than twice as long as penultimate segment, naked or with scattered setae dorsally. Basal segment with strong ventromesial spine; lateral face with distal subrectangular lobe armed with small spine, and strong spine proximally. Ventral flagellum with 6 articles.

Antennal peduncle ( Fig. 35A, B ) not exceeding distal margin of cornea, reaching at most to about distal 0.7 length of cornea. Fifth segment unarmed except for scattered setae and laterodistal tuft of setae. Fourth segment armed with strong dorsodistal spine. Third segment with strong ventromesial distal spine. Second segment with dorsolateral distal angle produced, terminating in strong, simple spine often with 1 or 2 small dorsal subterminal spines; mesial margin with spine on dorsodistal angle. First segment with lateral face usually armed with small spine; ventromesial angle produced, with 2 or 3 small spines laterally. Acicle relatively short, reaching to about midportion of cornea, nearly straight (in dorsal view), terminating in strong spine; mesial margin armed with 9 spines, sparsely setose. Flagellum slightly exceeding extended right cheliped, articles with setae 1 or 2 flagellar articles in length.

Mouthparts not dissected. Mandible with 3-segmented palp; cutting edge calcified, with small calcareous tooth medially; molar process with small calcareous tooth medially. Maxillule with external lobe of endopod obsolete, internal lobe with long, terminal seta. Maxilla with endopod not exceeding distal margin of scaphognathite. First maxilliped with endopod not exceeding exopod in distal extension. Second maxilliped without distinguishing characters. Third maxilliped with merus to dactyl each distinctly longer than broad, ischium about twice as long as broad; crista dentata with about 12 sharp teeth diminishing in strength distally, proximal 3 teeth distinctly larger than others; basis with 1 small mesial spine; coxa lacking spine. Sternite of third maxillipeds with small spine on each side of midline.

Chelipeds markedly dissimilar. Right cheliped ( Fig. 36A–C ) massive, chela operculate; dorsal surfaces of merus, carpus and chela with dense, finely plumose setae, setae more dense on fingers. Fingers curved ventromesially, each terminating in small, usually blunt corneous claw; cutting edges with 2 or 3 large calcareous teeth and several irregularly sized smaller sharp or blunt calcareous teeth, with closely set minute corneous teeth distally (corneous teeth interspersed with small calcareous teeth on fixed finger). Dactyl about as long as mesial margin of palm, set at strongly oblique angle to longitudinal axis of palm; mesial margin broadly curved, well delimited by row of strong, corneous-tipped spines diminishing in size distally; dorsal face with moderately dense small spines or tubercles decreasing in density distally; ventromesial face concave proximally. Fixed finger broad at base, dorsal face smooth and without spines or tubercles, lateral margin well delimited by row of corneous-tipped spines; ventrolateral face elevated along midline. Palm with distomesial angle mesially expanded, thumb-like ( Fig. 36A–C ), about as broad as long (if including expanded distomesial angle) or longer than broad (if excluding expanded distomesial angle); dorsal surface with scattered small spines or tubercles; dorsolateral margin nearly straight, well delimited by row of strong, mostly corneous-tipped calcareous spines, dorsomesial margin weakly delimited by row of small spines or tubercles; mesial face rounded, with numerous small spines or tubercles; ventral surface smooth or with scattered small tubercles. Carpus 1.7 times as long as broad, dorsal surfaces covered with small spines or tubercles, dorsodistal margin with row of small spines; dorsolateral face rounded and with 3 calcareous spines distally, dorsomesial face rounded; ventral face slightly concave, with scattered small tubercles or spines. Merus with small spines or tubercles on dorsal surfaces; scattered setae dorsally, and moderately dense setae ventrodistally; ventromesial margin with row of blunt to sharp spines. Ischium with ventromesial row of small, blunt spines. Coxa with ventromesial row of setae and 2 small spines on lateral angle of ventrodistal margin.

Left cheliped ( Fig. 36D, E ) evenly calcified, with moderately dense, long setae on merus, carpus and chela. Fingers each terminating in small corneous claw; dorsal and ventral surfaces unarmed except for scattered tufts of setae; cutting edge of dactyl with row of minute, fused corneous teeth; cutting edge of fixed finger with row of well-spaced small calcareous teeth. Dactyl about as long as length of mesial margin of palm. Palm unarmed except for dorsomesial row of small sharp or blunt spines; ventral face smooth. Carpus with strong dorsodistal spine; ventral face smooth. Merus unarmed dorsally except for setae; ventral face with 3 small spines distally. Ischium and coxa unarmed, but with ventromesial row of setae.

Ambulatory legs ( Fig. 37A–D ) similar right from left except for longer segments on right, extending to about tip of dactyls of right cheliped or slightly exceeding them; meri, carpi and propodi with setae on dorsal and ventral margins, dactyl also with distal row of dorsomesial setae. Dactyls ( Fig. 37B, D ) broadly curved, about 1.5 times as long as propodi, and terminating in sharp corneous claws; with 7–10 small spinules on ventromesial margin. Propodi unarmed except for setae. Carpi unarmed except for setae and small dorsodistal spine. Meri unarmed except for setae. Ischia with setae dorsally and ventrally, and small distal spine on ventral margin. Coxae with ventromesial row of setae. Anterior lobe of sternite XII (between second ambulatory legs, Fig. 35C ), setose, with subdistal spine.

Fourth pereopod ( Fig. 37E ) semichelate. Dactyl terminating in sharp corneous claw; with ventrolateral row of small corneous spinules. Propodus longer than broad, rasp with 1 row of rounded scales at least distally. Carpus with long setae on dorsal margin. Merus with rows of long setae on dorsal and ventral margins. Coxa with anteroventral row of setae. Anterior lobe of sternite XIII (between fourth pereopods, Fig. 35C ) with row of setae.

Fifth pereopod ( Fig. 37F ) semichelate. Propodal rasp extending beyond mid-length of segment. Coxa with row of long setae on anteroventral and ventrodistal margins. Anterior lobe of sternite XIII (between fourth pereopods, Fig. 35C ) with row of setae.

Telson and uropods markedly asymmetrical; left exopod ( Fig. 35D ) about 2.6 times as long as broad, rasp consisting of 3 or 4 rows of small scales. Telson ( Fig. 35E ) without or at most obsolete transverse suture; dorsal surface with scattered setae; lateral margins with long setae medially; posterior lobes separated by shallow unarmed, U-shaped cleft; terminal margin of left lobe armed with 13 corneous spines, some slightly curved and distal 2 or 3 strong, terminal margin of right lobe armed with 4 small spines.

Male with paired first and second gonopods ( Fig. 35C ); first gonopod with distal portion subovate, with setae distally; second with distal segment flat and with long setae distally, proximal segment with long setae distomesially. Female unknown.

Colouration. Unknown.

Habitat. The only specimen known was found in a gastropod shell.

Distribution. So far known only from the Norfolk Ridge, in the New Caledonia region. Depth: 527 m.

Remarks. Despite the existence of only one specimen, the

distinctive morphology of the right cheliped, especially the chela, is sufficient to propose a new species. The dorsolateral margin of the palm and fixed finger are nearly straight, and the distal angle of the mesial face is strongly produced mesially, appearing thumb-like and covered with small spines or tubercles. The cutting edges of the fingers are also different from other Oncopagurus species , in that the large teeth are sharp and serrated, whereas in other species the large teeth are blunt and rounded.

Etymology. The specific name is derived form the Latin, pollex, thumb, and is given in reference to the thumb-like projection on the distomesial angle of the right chela.

Figures

Fig. 35. Oncopagurus pollicis, new species, holotype, male 3.2 mm, New Caledonia, CHALCAL 2, sta DW 72 (MNHN-IU-5496): A, shield and cephalic appendages, dorsal; B, right antennal peduncle, lateral; C, sternum and coxae of first to fifth pereopods, and anterior portion of pleon with first and second gonopods, ventral; D, exopod of left uropod, dorsal; E, telson, dorsal. Scale bars = 0.5 mm (A, C), 0.25 mm (B), 1 mm (D, E).

Fig. 36. Oncopagurus pollicis, new species, holotype, male 3.2 mm, New Caledonia, CHALCAL 2, sta DW 72 (MNHN-IU-5496):A, right cheliped, dorsal; B, chela of same, ventral; C, dactyl, fixed finger, and distal portion of palm of right cheliped, ventral; D, left cheliped, dorsal; E, same lateral. Scale bars = 1 mm (A, B, D, E); 0.5 mm (C).

Fig. 37. Oncopagurus pollicis, new species, holotype, male 3.2 mm, New Caledonia, CHALCAL 2, sta DW 72 (MNHN-IU-5496): A, right first ambulatory leg, lateral; B, dactyl of same, mesial; C, right second ambulatory leg, lateral; D, dactyl of same, mesial; E, propodus and dactyl of left fourth pereopod, lateral; F, propodus and dactyl of left fifth pereopod, lateral. Scale bars = 1 mm (A–D); 0.25 mm (E, F).

Fig. 51. Bathymetric distribution of Oncopagurus species from the world, with maximum and minimum depths (meters) indicated for each.