Oncopagurus bifidus, 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 : 217-224

Oncopagurus bifidus , new species

Figs. 2–5 , 51

Oncopagurus n. sp. 4 – McLaughlin et al., 2010: 39.

Type material. Holotype, Philippines, MUSORSTOM 3, sta CP 96, 14°00'S, 120°17'E, 190–194 m, 1 June 1985: M 3.4 mm (MNHN-IU-2013-5584, ex MNHN Pg. 7569).

Paratypes, Philippines: MUSORSTOM 2: sta CP 2, 14°01'N, 120°17'E, 184–186 m, 20 November 1980: 1 M 2.8 mm (MNHN- IU-2013-5485, ex MNHN Pg. 7571); sta CP 10, 14°00'N, 120°18'E, 188–195 m, 21 November 1980: 2 M 2.4, 2.6 mm, 2 ov F 2.4, 2.5 mm (MNHN-IU-2013-5486, ex MNHN Pg. 7572), 1 M 2.2 mm, 1 F 1.8 mm (MNHN-IU-2013-5487, ex MNHN Pg. 7572), 2 M 2.0, 3.1 mm ( MNHN Pg.), 1 M 3.1 mm (MNHN-IU-2013-5488, ex MNHN Pg. 7572); sta CP 11, 14°00'S, 120°20'E, 194–196 m, 21 November 1980: 1 F 2.0 mm (MNHN-IU-2013-5489, ex MNHN Pg. 7573); sta CP 18, 14°00'N, 120°19'E, 188–195 m, 22 November 1980: 3 M 2.3–3.6 mm, 1 ov F 2.4 mm ( USNM 1207985 , ex MNHN Pg. 7574); sta CP 64, 14°01'N, 120°19'E, 191–195 m, 29 November 1980: 6 M 2.1–2.9 mm, 1 F 2.8 mm ( USNM 1207986 , ex MNHN Pg. 7575); sta CP 71, 14°00'N, 120°18'E, 189–197 m, 30 November 1980: 1 M 2.9 mm, 1 F 2.4 mm, 1 ov F 2.4 mm (MNHN-IU-2013-5490, ex MNHN Pg. 7576); sta CP 72, 14°01'N, 120°19'E, 182–197 m, 30 November 1980: 1 M 2.4 mm, 1 ov F 1.7 mm (MNHN-IU-2013-5491, ex MNHN Pg. 7577), 1 M 2.3, 1 F 2.2 mm (MNHN-IU-2013-5492, ex MNHN Pg. 7577); sta CP 76, 13°50'N, 120°28'E, 440–485 m, 1 December 1980: 1 F 2.3 mm (MNHN-IU-2013-5493, ex MNHN Pg. 7578). — MUSORSTOM 3: sta CP 96, 14°00'S, 120°17'E, 190–194 m, 1 June 1985: 5 M 2.4–3.0 mm, 1 F 2.7 mm, 4 ov F 1.9–2.9 mm (MNHN-IU-2013-5583, ex MNHN Pg. 7569) .

Description. Gills biserial. Shield ( Fig. 2A ) about as broad as long; dorsal surface weakly calcified on usually most of surface except on small areas on each lateral side, with scattered short setae; rostrum broadly rounded, weakly produced, with short mid-dorsal ridge; anterior margins weakly concave; lateral projections bluntly subtriangular, occasionally with small terminal spine; anterolateral margins sloping; posterior margin broadly rounded; ventrolateral margins of shield usually with small slender spine. Anterodistal margin of branchiostegite rounded, unarmed, setose.

Ocular peduncles ( Fig. 2A ) more than half length of shield, increasing in width distally, weakly calcified on lateral and mesial faces; with longitudinal row of setae dorsally. Cornea moderately dilated. Ocular acicles subtriangular, each terminating in strong spine; separated basally by about half basal width of 1 acicle.

Antennular peduncle ( Fig. 2A ) exceeding distal margin of cornea by nearly full length of ultimate segment. Ultimate segment about twice as long as penultimate segment, with scattered setae dorsally. Basal segment with strong ventromesial spine; lateral face with distal subrectangular lobe unarmed or with small spine and setae, and strong spine proximally. Ventral flagellum with 5 or 6 articles.

Antennal peduncle ( Fig. 2A, B ) reaching at most to about middle portion of cornea. Fifth segment unarmed except for scattered setae and distolateral tufts of setae. Fourth segment with small dorsodistal spine. Third segment with strong ventromesial distal spine. Second segment with dorsolateral distal angle produced, terminating in simple spine; mesial margin with spine on dorsodistal angle. First segment with lateral face unarmed or with small spine; ventromesial angle produced, with 2 or 3 small blunt spines laterally. Acicle nearly straight (in dorsal view), reaching at most to about proxinal margin of cornea, terminating in strong spine; mesial margin armed with 8–10 spines, setose. Flagellum long, slightly exceeding extended right cheliped, articles with long setae 1–2 flagellar articles in length every 3 or 4 articles, and scattered short setae <1 article in length.

Mandible ( Fig. 3A ) with 3-segmented palp; cutting edge calcified, with small corneous tooth medially; molar process with small corneous tooth medially. Maxillule ( Fig. 3B ) with external lobe of endopod slender, moderately developed, not recurved, internal lobe with long, terminal seta. Maxilla ( Fig. 3C ) with endopod exceeding distal margin of scaphognathite. First maxilliped ( Fig. 3D ) with endopod slightly exceeding exopod in distal extension. Second maxilliped ( Fig. 3E ) without distinguishing characters. Third maxilliped ( Fig. 3F, G ) with merus to dactyl each distinctly longer than broad, ischium less than twice as long as broad; crista dentata with about 10 often corneous-tipped teeth much stronger proximally than distally, and diminishing in size distally; basis with mesial spine; coxa lacking spine. Sternite of third maxillipeds with small spine on each side of midline. Epistomial spine slender, vertically bifid, with upper spine curved upward ( Fig. 2C ).

Chelipeds markedly dissimilar. Right cheliped ( Fig. 2D–F ) with chela operculate, sparsely setose except for dorsal surfaces of fingers and mesial faces of merus and carpus. Fingers curved ventromesially, terminating in small, usually blunt corneous claw; cutting edges each with 5 (dactyl) or 3 (fixed finger) large calcareous teeth, and several additional small calcareous teeth on fixed finger proximally. Dactyl shorter than mesial margin of palm in males, about same length as palm in females, set at oblique angle to longitudinal axis of palm; mesial margin broadly curved, well defined by row of small blunt or sharp spines diminishing in size distally; dorsal face unarmed except for moderately dense setae and sometimes scattered minute tubercles; ventromesial face concave, smooth. Fixed finger broad at base, dorsal and ventral faces unarmed except for moderately dense setae. Palm longer than broad in males, about as broad or slightly broader than long in females, dorsal surface smooth or at most with scattered small spines or tubercles; dorsolateral margin well delimited by row of small spines, dorsomesial margin with row of small spines or tubercles; mesial face flat or slightly concave ( Fig. 2F ), smooth or with scattered small tubercles, ventromesial margin with row of small spines or tubercles at least on proximal half; ventral surface smooth. Carpus longer than broad; dorsal surface with many small to minute spines or tubercles, dorsodistal margin with row of spines often extending to distomesial margin as larger spines; dorsolateral margin usually well defined by row of spines, often distally flared and upturned ( Fig. 2E ); dorsomesial margin rounded; ventromesial margin with row of small spines; ventral face with scattered small tubercles. Merus with scattered small spines or tubercles on dorsal surface and moderately dense setae dorsally and mesially; ventromesial and ventrolateral margins each with row of spines. Ischium with dorsal row of setae. Coxa ( Fig. 5A ) often with ventrolateral row of small tubercles, and ventromesial row of setae.

Left cheliped ( Fig. 2G ) usually weakly calcified on dorsolateral face of carpus and merus. Fingers terminating in small corneous claw, often gaping when closed; 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 subequal in length to mesial margin of palm. Palm unarmed except for 2 or 3 small dorsomedian spines distally, sparsely setose; ventral face smooth. Carpus with small distal spine on dorsal and dorsolateral margins, dorsal face setose; ventral face smooth. Merus with dorsal face setose and at most with 2 or 3 minute spines; ventromesial margin with row of 2–4 spines distally; ventral face smooth. Ischium and coxa unarmed or with small spine distally on ventrolateral margin; with ventromesial row of setae.

Ambulatory legs ( Fig. 4A–D ) slender, similar right from left except for longer, spinose meri on right, and lacking spines on left; exceeding extended right cheliped by at most about 0.2 length of dactyls. Dactyl broadly curved, about 1.8 times as long as propodus, and terminating in sharp corneous claw; with dorsal and dorsomesial distal rows of long setae, and ventromesial row of 1–8 minute or inconspicuous, corneous spinules. Propodus with row of long setae on dorsal margin, and scattered setae on ventral margin. Carpus with dorsal margin setose, unarmed or with 1–5 small spines, and small dorsodistal spine; ventral margin with scattered short setae. Merus with long setae on dorsal and ventral margins, lacking spines on dorsal margin (left second and third), or with 1 or 2 (right second) or 3–7 (right third) minute spines on dorsal margin. Ischium unarmed except for setae on dorsal and ventral margins, and small ventrodistal spine. Coxa ( Fig. 5A ) with row of spines on anteroventral margin proximally (second) or lacking spines (third), and ventromesial row of setae. Anterior lobe of sternite XII (between second ambulatory legs, Fig.5A ) subsemicircular, setose, with distinct spine.

Fourth pereopod ( Fig. 4E ) semichelate. Dactyl broadly curved, 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. 5A ) with row of long setae.

Fifth pereopod ( Fig. 4F ) semichelate. Propodal rasp extending to mid-length of segment. Coxa with dense row of long setae on anteroventral and distoventral margins. Anterior lobe of sternite XIV (between fifth pereopods; Fig. 5A ) with row of long setae.

Uropods and telson strongly asymmetrical; left uropod ( Fig. 5B ) with narrow rasp consisting of 2 or 3 rows of corneous scales. Telson ( Fig. 5C–E ) lacking transverse suture; dorsal surface with scattered setae, lateral margins with long setae; posterior lobes separated by inconspicuous or shallow U-shaped cleft, left lobe considerably longer than right; terminal margins of lobes armed with slender, corneous spines stronger and more numerous in females than in males, and extending nearly to midportion of left lateral margin; left lobe with about 16–20 long and short spines, 2 or 3 of which are strongest and strongly curved or bent at nearly right angle; right lobe with about 5 short spines.

Male lacking first gonopods; with paired, asymmetrical second gonopod ( Fig. 2H ), left short, 1-segmented, right vestigial (occasionally absent). Female without vestigial second right pleopod.

Colouration. Unknown.

Habitat. Gastropod shells.

Distribution. Western tropical Pacific, so far known only from the Philippines. Depth: 182– 485 m.

Remarks. This new species is unique in having a vertically bifid epistomial spine, with the upper spine curved upward. Other characters that set this new species apart from other congeners are: the ocular peduncles which are slightly constricted medially; the length of the antennal acicles that reach at most to about the proximal margin of the corneas; the noticeably slender ambulatory legs and long dactyls, relative to other congeners; the narrow rasp of the left uropod; the armature of the telson, with a left posterior lobe much longer than the right, and in females the left lobe is armed with often strikingly slender, short to long corneous spines arranged in several uneven rows.

Etymology. The specific name is derived from the Latin, bi, two, and –fid, divided into many parts, and makes reference to the bifid shape of the epistomial spine, a unique character among species of Oncopagurus .

Figures

Fig. 2. Oncopagurus bifidus, new species, Philippines: A–F, holotype, male 3.4 mm, MUSORSTOM 3, sta CP 96 (MNHN-IU-2013-5584, ex MNHN Pg 7569); G, paratype, ov female 2.8 mm, same sta (MNHN-IU-2013-5583, ex MNHN Pg 7569); H, paratype, male 2.4 mm, sta CP 72 (MNHN-IU-2013-5491, ex MNHN Pg 7577). A, shield and cephalic appendages, dorsal; B, right antennal peduncle, lateral; C, epistome, laterodorsal; D, right cheliped of male, dorsal; E, right cheliped of female, dorsal; F, chela of same, mesial; G, left cheliped, dorsal; H, left second gonopod, lateral. Scale bars = 1 mm (A, D–G); 0.5 mm (B); 0.25 mm (C).

Fig. 3. Oncopagurus bifidus, new species, Philippines: paratype, male 2.8 mm, MUSORSTOM 3, sta CP 96 (MNHN-IU-2013-5583, ex MNHN Pg 7569). Left mouthparts, internal: A, mandible; B, maxillule; C, maxilla; D, first maxilliped; E, second maxilliped; F, third maxilliped; G, ischium and crista dentata of same. Scale bars = 0.25 mm (A–D, G); 0.5 mm (E, F).

Fig. 4. Oncopagurus bifidus, new species, Philippines, holotype, male 3.4 mm, MUSORSTOM 3, sta CP 96 (MNHN-IU-2013-5584, ex MNHN Pg 7569). 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 right fourth pereopod, lateral; F, propodus and dactyl of right fifth pereopod, lateral. Scale bars = 1 mm (A–D); 0.25 mm (E, F).

Fig. 5. Oncopagurus bifidus, new species, Philippines: A–C, holotype, male 3.4 mm, MUSORSTOM 3, sta CP 96 (MNHN-IU-2013-5584, ex MNHN Pg 7569); D, E, paratype, ov female 2.8 mm, same sta (MNHN-IU-2013-5583, ex MNHN Pg 7569). A, sternum and coxae of first to fifth pereopods, ventral; B, exopod of left uropod, dorsal; C, telson of male, dorsal; D, E, telson of female, dorsal (D) and posterior (E). Scale bars = 1 mm (A); 0.5 (D, E); 0.5 mm (B, C).

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