Pagurixus vicinus, Osawa & Kawai & Sakamaki, 2013

Osawa, Masayuki, Kawai, Takashi & Sakamaki, Takashi, 2013, New records of Pagurixus Melin, 1939 (Crustacea: Decapoda: Paguridae) from the Ryukyu Islands, southwestern Japan, with description of a new species, Zootaxa 3669 (3), pp. 350-366 : 358-364

Pagurixus vicinus sp. nov.

( Figs 1E, F , 4–6 )

[New Japanese name: Irowake-himehonyardokari]

Type material. Holotype. Akuseki-jima, Tokara Group: stn A 1-1, 29°26.8´N, 129°35.6´E, 7 m, 23 Jul. 2012, coll. T. Kawai, male (sl 1.4 mm), RUMF-ZC 2345 .

Paratypes. Kuchino-shima, Tokara Group: stn K 2-1, 30°00.5´N, 129°55.0´E, 7 m, 26 Jul. 2012, coll. T . Kawai, 3 males (sl 0.9–1.4 mm), 1 female (sl 0.9 mm), 2 ovig. female (sl 1.1, 1.2 mm), RUMF-ZC 2346 ; stn K 2-2, 30°00.5´N, 129°55.0´E, 7 m, 27 Jul. 2012, coll. T . Kawai, 3 females (sl 1.2–1.4 mm), RUMF-ZC 2347 . Akusekijima, Tokara Group: stn A 2-2, 29°27.3´N, 129°37.2´E, 7 m, 24 Jul. 2012, coll. T . Kawai, 1 male (sl 0.9 mm), 1 female (sl 1.1 mm), RUMF-ZC 2348 ; stn A 3-2, 29°28.4´N, 129°36.5´E, 7 m, 24 Jul. 2012, coll. T . Kawai, 1 male (sl 1.0 mm), RUMF-ZC 2349 .

Additional material. Kuchino-shima, Tokara Group: stn K 1-1, 29°59.1´N, 129°55.7´E, 7 m, 26 Jul. 2012, coll. T . Kawai, 1 female (sl 0.9 mm), RUMF-ZC 2350 ; stn K 1-2, 29°59.1´N, 129°55.7´E, 7 m, 27 July 2012, coll. T . Kawai, 1 female (sl 1.2 mm), RUMF-ZC 2351 . Akuseki-jima, Tokara Group: stn A 3-1, 29°28.4´N, 129°36.5´E, 7 m, 23 Jul. 2012, coll. T . Kawai, 1 ovig. female (sl 1.2 mm), RUMF-ZC 2352 . Takara-jima, Tokara Group: stn T 1-1 , 29°07.7´N, 129°13.3´E, 7 m, 20 Jul. 2012, coll. T . Kawai, 1 female (sl 1.3 mm), RUMF-ZC 2353 ; stn T 2- 1 , 29°09.5´N, 129°13.3´E, 7 m, 20 Jul. 2012, coll. T . Kawai, 1 female (sl 1.1 mm), RUMF-ZC 2354 .

Description. Shield ( Fig. 4A ) approximately 1.1 times longer than wide; anterior margin between rostrum and lateral projections concave; anterolateral margins sloping; posterior margin roundly truncate; dorsal surface smooth, with few tufts of short setae laterally. Rostrum triangular, reaching nearly to midlength of ocular acicles, moderately broad, terminating bluntly or acutely. Lateral projections obtuse, each with submarginal spinule.

Ocular peduncles ( Fig. 4A ) moderately stout, 0.7 length of shield, each with few tufts of short setae on dorsomesial surface; middle portion slightly inflated on mesial surface, subequal to corneal width; corneas not dilated, corneal width 0.3 of peduncular length. Ocular acicles subtriangular, each with submarginal spinule.

Antennular peduncles ( Fig. 4A ) overreaching distal corneal margins by 0.2–0.3 lengths of ultimate segments. Ultimate segment with tuft of few setae near dorsolateral distal angle, ventral surface lacking longitudinal rows of setae. Basal segment with small spine on distal margin of statocyst lobe. Ventral flagellum with few short setae on lateral and mesial margins.

Antennal peduncles ( Fig. 4A ) overreaching distal corneal margins by 0.2–0.3 lengths of fifth segments. Fifth and fourth segments with few tufts of short setae. Third segment with small spine at distomesial angle. Second segment with or without minute spine at dorsomesial distal angle; laterodistal projection not reaching midlength of fourth segment, terminating in simple or bifid spine. First segment unarmed on lateral face; ventromesial distal margin strongly produced, with small spine. Antennal acicle arcuate, terminating in small spine, overreaching base but not reaching distal margin of cornea; mesial margin with row of sparse setae.

Third maxilliped moderately stout; ischium with well developed, crista dentata composed of row of small corneous teeth and 1 accessory tooth; merus and carpus unarmed; exopod reaching distal margin of carpus.

Male right cheliped ( Figs 4B, C, E , 5A, B , 6A, B ) large, not particularly elongate. Chela subovate in dorsal view, 1.7–1.9 times as long as wide. Dactylus slightly longer than or equal in length to palm, terminating in small corneous claw; dorsomesial margin not delimited; dorsal, ventral, and mesial surfaces with scattered small granules and short setae, obsolete longitudinal ridge present proximally on mesial surface; cutting edge with 3 blunt calcareous teeth in proximal 0.7 and row of short corneous teeth in remaining margin. Palm 1.0–1.1 times length of carpus; convex dorsal surface generally covered with small granules; dorsolateral margin delimited by weak or distinct granular ridge extending onto fixed finger; dorsomesial margin also delimited by series of short granular ridges or sharp, generally uninterrupted ridge; lateral surface with scattered, coarse granules; mesial and ventral surfaces also with sparse granules. Fixed finger terminating in small calcareous or corneous claw; cutting edge with row of blunt calcareous teeth, median tooth prominent. Carpus nearly equal in length to merus, widened distally, length 1.0–1.1 times of distal width; dorsal surface with several or many, short transverse ridges distally and with sparse, short, bristle-like stiff setae and short simple setae, irregular row of small to moderately large spines present adjacent to proximal half of dorsomesial margin, dorsolateral surface rounded; dorsomesial margin delimited by row of short, somewhat elevated ridges bearing bristle-like stiff setae and with or without small spine near distal end; dorsodistal margin with row of small low tubercles; lateral surface with very short vertical ridges ventrally, ventrolateral margin with row of obsolete tubercles distally; mesial surface nearly smooth, ventromesial margin with row of low tubercles or granules distally; ventral surface convex, with sparse setae distally. Meral-carpal articulation lacking any pronounced clockwise rotation. Merus with median row of short and very short transverse ridges on dorsal surface, dorsodistal margin with few short setae; lateral face nearly smooth, ventrolateral margin distally with row of small sharp or blunt spines; mesial face also nearly smooth, convex ventromesial margin slightly protuberant but unarmed; ventral surface smooth, with short setae. Ischium with smooth ventromesial margin; surfaces unarmed, with sparse short setae.

Female right cheliped ( Figs 4D, F , 5C, D , 6C ) relatively slender for genus, stouter but only slightly longer than or equal in length to left. Chela elongate subovate in dorsal view, 1.7–2.1 times longer than wide, with arched lateral margin. Dactylus longer than palm, terminating in small corneous claw; surfaces bearing sparse short setae; dorsal surface with few short ridges proximally, dorsomesial margin weakly or distinctly delimited by blunt ridge of low tubercles; ventral surface nearly smooth; cutting edge with row of small corneous teeth. Palm distinctly shorter than carpus; dorsal surface weakly convex, with slightly elevated row of small tubercles adjacent to dorsomesial margin and irregular double row of tubercles lateral to midline, some low tubercles also present on proximal and distal parts, tubercles occasionally bearing short setae; dorsolateral margin delimited by distinct tuberculate ridge extending onto midlength of fixed finger; dorsomesial margin also delimited by distinct, generally uninterrupted tuberculate ridge; lateral surface with scattered, short ridges; mesial surface with some oblique ridges dorsally; ventral surface slightly protuberant, with sparse short setae. Fixed finger terminating in small corneous claw; cutting edge with row of tiny calcareous teeth and interspersed with short corneous teeth. Carpus subequal in length to merus, widened distally, length 1.7–1.9 times of distal width; dorsal surface laterally with row of short low ridges, mesially with 3 distal spines followed by slightly elevated, short ridges, each spine and ridge occasionally with bristle-like stiff seta or short simple setae, dorsodistal margin with small low tubercles; mesial surface dorsally with longitudinal row of slightly elevated, short ridges each bearing bristle-like stiff seta or simple setae; lateral surface with scattered, short vertical ridges, ventrolateral margin with 2 or 3 small spines distally; mesial surface with few short ridges dorsally and ventrally, ventromesial margin unarmed; ventral surface convex, with few short setae. Meral-carpal articulation lacking any pronounced clockwise rotation. Merus with median row of short transverse ridges on dorsal surface, dorsodistal margin with few short setae; lateral face with scattered, very short vertical ridges, ventrolateral margin with 2 or 3 small spines on distal half; mesial face nearly smooth, ventromesial margin unarmed; ventral surface slightly convex, with few short setae. Ischium nearly smooth, with sparse setae.

Left cheliped ( Figs 4G, H , 5E, F ) similar in both males and females, moderately short and stout. Chela elongate subovate in dorsal view, 2.2–2.6 times longer than wide. Dactylus distinctly longer than palm, terminating in small corneous claw; surfaces with scattered tufts of setae, ventral setae long; dorsal, ventral, and mesial surfaces rounded; mesial surface also with few short ridges proximally; cutting edge with row of sharp corneous teeth. Palm 0.5–0.6 length of carpus; dorsal surface convex, with lateral and mesial rows of small spines or tubercles, mesial row somewhat elevated, dorsolateral surface with some small tubercles; dorsolateral and dorsomesial margins not delimited; lateral and mesial surfaces with short, oblique ridges bearing short to moderately long setae; ventral surface weakly convex, with sparse tufts of setae distally. Fixed finger terminating in small corneous claw, cutting edge with row of small corneous teeth. Carpus somewhat compressed laterally, shorter than merus; length 1.9–2.4 times of width and 1.6–1.8 times of height; dorsal surface flattish, dorsolateral and dorsomesial margins each with 2 or 3 small distal spines followed by short ridges each bearing 1 or 2 bristle-like stiff setae, dorsodistal margin with 1 or 2 small spines flanked by spines in dorsolateral and dorsomesial rows; lateral face nearly perpendicular, dorsally with few short ridges each bearing bristle-like stiff seta and ventrally with scattered, very short ridges, ventrolateral margin with 1–3 small spines distally; mesial face also dorsally with short ridges each bearing bristlelike stiff seta and few simple setae, ventromesial distal margin slightly protuberant; ventral surface convex, with sparse short setae, ventrodistal margin with row of moderately long setae. Merus with median row of short obsolete ridges on dorsal surface, dorsodistal margin unarmed but bearing few short setae; lateral surface with many, very short vertical ridges, ventrolateral margin with row of small spines and moderately long setae in distal half; mesial surface nearly smooth, bearing few short setae, ventromesial margin unarmed but with row of moderately long setae; ventral surface weakly convex, smooth. Ischium unarmed, with sparse short setae.

Ambulatory legs ( Fig. 6D–K ) similar on right and left (right slightly longer than left) and between males and females, moderately slender. Dactyli 0.7–0.9 length of propodi, 4.6–5.2 (second pereopods) or 5.1–6.4 (third pereopods) times longer than wide, terminating in large corneous claws; dorsal surfaces with few short setae; lateral and mesial faces also with sparse tufts of short setae adjacent to dorsal and ventral margins; ventral margins each with 5–7 slender corneous spines increasing in size distally. Propodi not tapering distally, 3.7–4.3 (second pereopods) and 3.9–5.1 (third pereopods) times longer than wide; dorsal surfaces nearly smooth, with row of sparse short setae; lateral and mesial faces also with few short setae dorsally and ventrally; ventral margins weakly curved, each with 1–4 (usually 1 or 2, right second pereopod), 0–2 (usually 1 or 2, left second), 1–7 (usually 1 or 2, right third), and 1 or 2 (left third) corneous spinules; ventrodistal margin with 1 or 2 corneous spines larger than spines on ventral margin. Carpi each with small dorsodistal spine; dorsal surfaces unarmed but slight protuberant, bearing sparse short setae; lateral and mesial faces also with few short setae; ventrodistal margins rounded, not produced. Meri each with row of short low ridges bearing sparse short setae on dorsal margin; lateral and mesial surfaces nearly smooth; ventral margins somewhat inflated on distal third, ventrolateral margins each with small subdistal spine (second pereopods) or unarmed (third pereopods).

Fourth pereopods ( Fig. 4I ) subequal in size on right and left and between males and females; in males, setation similar on right and left, but in females, setae somewhat longer on left. Dactyli moderately broad, not curved, terminating in small corneous claws; dorsal margins with sparse setae. Propodi each with tuft of few setae on dorsal margin; mesial faces nearly flat; propodal rasp composed of single row of corneous scales. Carpi with sparse setae on margins.

Coxae of fifth pereopods in males ( Fig. 4K ) unequal and dissimilar. Right coxa with short but distinct, collarlike posteromesial protrusion; prominent tuft of long stiff setae arising from ventrodistal margin of protrusion, reaching to left coxa; papilla-like vas deferens present at top of posteromesial protrusion. Left coxa with gonopore encircled by short setae, no protrusion of vas deference seen. Female with unpaired left gonopore.

Anterior lobe of sixth thoracic sternite ( Fig. 4J ) subrectangular, with row of short to long setae anteriorly; anterolateral angles rounded. Eighth thoracic sternite ( Fig. 4K ) composed of 2 subequal, closely-set rounded lobes; ventral surface of each lobe flattened, with sparse short setae anteriorly.

Pleon without distinctive features. Telson ( Fig. 4L ) with terminal margins oblique or nearly horizontal and each bearing 2–4 small spines; dorsal surface adjacent to terminal margins slightly elevated, well calcified.

Coloration in life. Carapace translucent; shield with pair of small brown spots posterior to base of ocular peduncles and brown marking on posterior part; posterior carapace without distinct color markings. Ocular peduncles translucent, with brown tinge proximally and irregular brown markings on lateral and mesial surfaces; ocular acicles whitish. Antennular peduncles with submedian brown band on penultimate segment; ultimate segment with 2 brown rings on proximal and distal portions, median portion and proximal and distal marginal portions colorless; flagella pale orange. Antennal peduncle generally translucent; second, third, and fourth segments each with submedian brown marking; fifth segment marginally brown; flagellum translucent, light brown on margins. Right cheliped generally white; palm and carpus with some brown spots or blotches on dorsal and mesial surfaces; merus dorsally with narrow, subdistal brown ring and subproximal brown blotch. Left cheliped white; dactylus and fixed finger with tingle of pale brown; palm and carpus with some brown spots on dorsal and mesial surfaces; merus dorsally with narrow, subdistal brown ring and subproximal brown blotch. Ambulatory legs banded with white and dark brown; dactyli dark brown in proximal 0.4–0.5 (in holotype, small white blotch present on dorsal margin), remaining portion white; propodi each with broad, dark brown band occupying about proximal 0.7, band sometimes bearing white blotch dorsally; carpi with brown blotches on proximal 0.7; meri each with 2 complete or incomplete bands distally and proximally; ischia each with brown blotches. See Fig. 1E, F .

Distribution. Presently known only from Akuseki-jima, Kuchino-shima, and Takara-jima, Tokara Group in the northern Ryukyus; 7 m.

Habitat. Coral reef slopes.

Etymology. The specific name is derived from the Latin, vicinus (= near), referring to the similarity in both morphology and coloration between the new species and P. fasciatus .

Remarks. Male specimens of the new species appear to have variations in the degree of the marginal delimitation on the right chela and the shape of the anterior lobe of the sixth thoracic sternite. The dorsolateral margin of the right chela is delimited by a weak granular ridge in the holotype, whereas the ridge is distinct in other males. The dorsomesial margin of the right palm in the holotype has a series of short granular ridges, instead of a sharp, generally uninterrupted ridge observed in the others. The anterior lobe of the sixth thoracic sternite is broader in the holotype compared to the other males. However, all males of the type series are undoubtedly conspecific because of the same color pattern.

McLaughlin & Haig (1984) divided the genus Pagurixus into two informal species groups based on the presence or absence of distinct row(s) of setae on the ventral surface of the ultimate segment of the antennular peduncle. Later, Komai & Osawa (2006) named them “ P. boninensis ” and “ P. anceps ” species groups. Pagurixus vicinus sp. nov. is referred to the P. anceps species group, which is characterized by the absence of longitudinal rows or series of setae on the ventral surface of the antennular ultimate segment. In this species group, P. vicinus sp. nov. closely resembles P. fasciatus . Shared characters are: ocular peduncles relatively short and exceeded by antennular and antennal peduncles; right cheliped with distinct dorsomesial spines but unarmed dorsolaterally on carpus in males and females; male right cheliped massive, without distinctly delimited dorsomesial margin on dactylus but bearing delimited granular ridge on dorsomesial margin of palm; left cheliped with dorsolateral and ventrolateral spines on carpus and ventrolateral row of spines on merus; third and fourth pereopods generally similar on right and left; coxa of right fifth pereopod in males with short but distinct, collar-like posteromesial protrusion; and female with unpaired left gonopore. In addition to these morphological features, the color patterns of the new species and P. fasciatus are also very similar, particularly in the possession of a broad dark brown band occupying about proximal 0.7 of the propodus of each ambulatory leg. However, P. vicinus sp. nov. is distinguishable from P. fasciatus by the armature on the left cheliped and right second pereopod based on the comparisons of the present specimens of the two species and with the illustrations of the type specimens of P. fasciatus by Komai & Myorin (2005). The carpus of the left cheliped is armed with fewer spines on the ventrolateral margin in the new species than in P. fasciatus (one to three versus four to six spines). The ventral margins of the dactylus and propodus of the right second pereopod also have fewer spines in P. vicinus sp. nov. than in P. fasciatus , i.e., five or six versus seven to nine spines on the dactylus and one to four (usually one or two) versus five to ten spines on the propodus, respectively. Additionally, in females, the dorsal margin of the carpus of each second pereopod is slightly protuberant but is always unarmed (exclusive of a dorsodistal spine) in the new species, whereas it bears a small submedian spine in P. fasciatus . In fresh condition, the two species are readily discriminated by the color patterns of the antennular peduncles and the dactyli of the ambulatory legs ( Fig. 1C–F ). The ultimate segment of the antennular peduncle has two brown rings on the proximal and distal portions in P. vicinus sp. nov., instead of being entirely brown in P. fasciatus . The dactyli of the ambulatory legs are dark brown on the proximal two-fifths to half and white on the remaining portion in the new species, whereas they are mostly dark brown and pale-colored on the midline in P. fasciatus . The shield of P. vicinus sp. nov. also lacks a posterolateral pair of brown spots, which are present in P. fasciatus .

General morphology and coloration also link P. vicinus sp. nov. to P. acanthocarpus . However, the new species differs from P. acanthocarpus in having apparently weaker, granulation and sculpture on the dorsal surface and margins of the right chela and armature on the dorsal surface of the carpus of the right cheliped (cf. Komai & Okuno 2009: figs 6A, 7A). Additionally, there are no marked sexual differences on the left chela and third pereopods in the new species, unlike in P. acanthocarpus . The palm of the left cheliped of P. acanthocarpus has a much more strongly arched and ridged lateral margin and a more prominently elevated dorsal surface in females than in males. The right and left third pereopods of P. acanthocarpus are generally similar in males, but in females, the left propodus is much stouter than the right and the left carpus bears a distinct row of setae on the laterodistal margin, which is absent on the right carpus. In males, the dorsal margin of the carpus of each second pereopod is unarmed (exclusive of a dorsodistal spine) in P. vicinus sp. nov., but it has at least one additional spine in P. acanthocarpus . Some details of the color pattern are also different between the two species ( Fig. 1A, B, E, F ). For instance, the posterolateral pair of brown spots on the shield as seen in P. acanthocarpus is absent in the new species. The dark brown band on the propodus of each ambulatory leg is broad and occupies about proximal 0.7 portion of the segment in P. vicinus sp. nov., whereas it is narrow and present only on about proximal 0.3 portion in P. acanthocarpus .

Figures

FIGURE 1. Entire animal, dorsal view. A, Pagurixus acanthocarpus Komai & Okuno, 2009, male (sl 1.8 mm), stn Sumiyoshi 2, Tanega-shima, RUMF-ZC 2324; B, Pagurixus acanthocarpus Komai & Okuno, 2009, ovig. female (sl 1.6 mm), stn Sumiyoshi 2, Tanega-shima, RUMF-ZC 2324 (pleon missing); C, Pagurixus fasciatus Komai & Myorin, 2005, male (sl 1.7 mm), stn Sumiyoshi 2, Tanega-shima, RUMF-ZC 2331; D, Pagurixus fasciatus Komai & Myorin, 2005, female (sl 1.4 mm), stn Sumiyoshi 2, Tanega-shima, RUMF-ZC 2331 (right third pereopod and pleon missing); E, Pagurixus vicinus sp. nov., paratype, male (sl 1.4 mm), stn K 2-1, Kuchino-shima, RUMF-ZC 2346; F, Pagurixus vicinus sp. nov., paratype, ovig. female (sl 1.2 mm), stn K 2-1, Kuchino-shima, RUMF-ZC 2346.

FIGURE 4. Pagurixus vicinus sp. nov., holotype, male (sl 1.4 mm), stn A 1-1, Akuseki-jima, RUMF-ZC 2345 (A, B, E, G, H, J–L); paratype, male (sl 1.4 mm), stn K 2-1, Kuchino-shima, RUMF-ZC 2346 (C, I), paratype, female (sl 1.1 mm), stn A 2-2, Akuseki-jima, RUMF-ZC 2348 (D, F). A, shield and cephalic appendages, dorsal view (setae omitted from right side); B, C, D, right chela, dorsal view; E, F, right cheliped, carpus, dorsal view; G, left chela, dorsal view; H, left cheliped, carpus, dorsal view; I, left 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. Scales: 0.5 mm.

FIGURE 5. Pagurixus vicinus sp. nov., holotype, male (sl 1.4 mm), stn A 1-1, Akuseki-jima, RUMF-ZC 2345 (A, B, E, F); paratype, female (sl 1.1 mm), stn A 2-2, Akuseki-jima, RUMF-ZC 2348 (C, D). A, C, right cheliped, lateral view; B, D, same, mesial view; E, left cheliped, lateral view; F, same, mesial view. Scales: 0.5 mm.

FIGURE 6. Pagurixus vicinus sp. nov., paratype, male (sl 1.4 mm), stn K 2-1, Kuchino-shima, RUMF-ZC 2346 (A, B); paratype female (sl 1.4 mm), stn K 2-2, Kuchino-shima, RUMF-ZC 2347 (C); holotype, male (sl 1.4 mm), stn A 1-1, Akusekijima, RUMF-ZC 2345 (D–K). A, right chela, mesial view; B, same, lateral view; C, right chela, mesial view; D, left second pereopod, lateral view; E, same, carpus, mesial view; F, same, dactylus, mesial view; G, right second pereopod, dactylus and propodus, lateral view (setae omitted); H, same, carpus, mesial view (setae omitted); I, left third pereopod, lateral view; J, same, dactylus, mesial view (setae omitted); K, right third pereopod, dactylus and propodus, lateral view (setae omitted). Scales: 0.5 mm.