Pagurixus fasciatus, Komai, Tomoyuki & Myorin, Eiji, 2005

Komai, Tomoyuki & Myorin, Eiji, 2005, A new species of Pagurixus (Crustacea: Decapoda: Anomura: Paguridae) from Southern Japan, Zootaxa 876, pp. 1-12: 2-10

publication ID 10.5281/zenodo.170889

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scientific name

Pagurixus fasciatus

n. sp.

Pagurixus fasciatus   n. sp. ( Figs. 1–4 View FIGURE 1 View FIGURE 2 View FIGURE 3 View FIGURE 4 )

[new Japanese name: Kashiwajima­hime­hon­yadokari]

Type material. HOLOTYPE: CBM­ZC 7980, male (SL 1.6 mm), Kashiwa­jima Islet, Ohtsuki, located at southwestern part of Shikoku, southern Japan, 10–15 m, 3 July 2004, SCUBA diving, coll. E. Myorin. PARATYPES: CBM­ZC 7981, 2 males (SL 1.3, 1.3 mm), 1 female (SL 1.0 mm), same data as holotype; CMNH­ZC 929, 1 female (SL 1.4 mm), Kyokucho­hama, Hachijo Island, Izu Islands, 31 m, 4 July 2002, SCUBA diving, coll. K. Tanaka; CMNH­ZC 1780, 1 female (SL 1.5 mm), same data; CMNH­ZC 1732, 1 male (SL 1.4 mm), Akinohama, Izu­Oshima Island, Izu Islands, 12 m, 24 February 2004, SCUBA diving, coll. H. Arima.

Description. Eleven pairs of biserial phyllobranchiae.

Shield ( Fig. 2 View FIGURE 2 A) about 1.1 times as long as broad; anterior margin between rostrum and lateral projections moderately concave; anterolateral margins sloping; posterior margin truncate; dorsal surface polished, with few tufts of short setae laterally. Rostrum triangular, reaching midlength of ocular acicles, moderately slender, terminating in acute spine. Lateral projections obtusely triangular, with or without small submarginal spinule.

Ocular peduncles ( Fig. 2 View FIGURE 2 A) relatively slender and moderately long, 0.6–0.7 length of shield, each with row of sparse tufts of short setae on dorsal surface mesially; corneas not dilated, corneal width about 0.3 of peduncular length; basal part slightly inflated, slightly broader than corneal width. Ocular acicles subovate or subtriangular, with small submarginal spine, moderately separated basally.

Antennular peduncles ( Fig. 2 View FIGURE 2 A) overreaching distal margins of corneas by 0.2–0.3 length of ultimate segment. Ultimate segment ( Fig. 2 View FIGURE 2 B) with 1 or 2 short setae at dorsolateral angle; ventral surface with row of sparse, very short setae, but lacking 2 rows of setal tufts or longitudinal setal bands. Basal segment unarmed.

Antennal peduncles ( Fig. 2 View FIGURE 2 A) just reaching or slightly overreaching distal margins of corneas. Fifth and fourth segments with few, short, stiff setae. Third segment with small spine at ventromesial distal angle. Second segment with small spine at dorsomesial distal angle; laterodistal projection short, not reaching midlength of fourth segment, terminating in simple or bifid spine. First segment with small laterodistal spine; ventromesial distal margin produced, unarmed or with 1 spinule just lateral to antennal gland opening. Antennal acicle short, arcuate, slightly overreaching base of cornea; mesial margin with few very short 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 overreaching distal margin of carpus.

Right cheliped of males ( Fig. 3 View FIGURE 3 A –D) stout. Chela subovate in dorsal view, about 1.7 times longer than broad. Dactylus subequal in length to palm; dorsomesial margin not delimited; surfaces covered with minute granules; cutting edge with 2 small calcareous teeth in proximal half and row of small corneous teeth in distal half, terminating in small calcareous claw. Palm longer than carpus; strongly convex dorsal surface covered with minute granules, dorsolateral margin delimited by faint ridge; mesial margin somewhat expanded, with sharp, granulate ridge over entire length; lateral, ventromesial, and ventral surfaces microscopically granular, almost naked; ventral surface weakly inflated, but mesial part nearly flat. Cutting edge of fixed finger with row of small calcareous teeth, interspersed by short rows of small corneous teeth, terminating in small calcareous claw. Carpus subequal in length to merus; dorsolateral and dorsomesial margins not delimited; all surfaces microscopically granular; dorsomesial face with irregular row of small spines; lateral face with very small, low tubercles, ventrolateral distal margin with short row of small tubercles adjacent to articular knob; mesial surface dorsally with small tubercles and short, denticulate longitudinal ridges, ventromesial distal margin weakly tuberculate; ventral surface convex. Meral­carpal articulation lacking any pronounced clockwise rotation; dorsal surface of merus almost smooth, dorsodistal margin also smooth; lateral and mesial faces smooth, ventrolateral and ventromesial margins smooth or faintly denticulate; ventral surface with few short setae. Ischium with smooth ventromesial margin; surfaces unarmed.

third pereopod, lateral view. Scales = 0.5 mm.

Right cheliped of female ( Fig. 4 View FIGURE 4 A –C) moderately short and stout. Chela about 1.6 times longer than broad. Dactylus slightly longer than palm, mesial margin delimited by lobate ridge; cutting edge with row of small corneous teeth in distal half, terminating in small corneous claw. Palm much shorter than carpus; dorsal surface weakly convex, microscopically granular, with longitudinal row of 3 low tubercles adjacent to dorsomesial margin; dorsomesial margin with sharp, granular ridge; dorsolateral margin also sharply carinate, strongly convex in dorsal view; lateral, mesial and ventral surfaces microscopically granular. Carpus slightly longer than merus; dorsomesial margin weakly delimited by row of 4 large spines; dorsal surface with scattered small tubercles and short transverse ridges, sloping to lateral face; ventrolateral distal margin weakly tuberculate; mesial face nearly smooth, ventromesial distal margin smooth; ventral surface convex. Merus smooth on surfaces; ventrolateral and ventromesial margins unarmed; ventral surface slightly convex, with few short setae. Ischium unarmed.

Left cheliped ( Fig. 3 View FIGURE 3 E –G) moderately stout. Chela 2.3 times longer than broad, 1.1–1.2 length of carpus. Dactylus longer than palm, with sparse tufts of short setae on surfaces (setae on ventral surface longest); dorsal surface almost smooth; cutting edge with row of small corneous teeth, terminating in small corneous claw. Palm about half length of carpus; dorsal surface somewhat elevated in mid­line, but not forming distinct ridge or crest, bearing scattered tiny tubercles, dorsolateral and dorsomesial margins not delimited; lateral surface with scattered simple or multifid tubercles; mesial face with few tiny tubercles; ventral surface nearly smooth, with tufts of long setae. Cutting edge of fixed finger with row of small corneous teeth. Carpus moderately stout, somewhat compressed laterally, about twice length of distal width and 1.6 length of greatest height, shorter than merus; dorsolateral and dorsomesial margins each with row of small spines; lateral surface perpendicular, with scattered small tubercles, ventrolateral margin with row of small spines; mesial face with short, oblique ridges dorsally, but otherwise nearly smooth, ventromesial distal margin unarmed; ventral surface convex, with long setae. Merus smooth on dorsal margin; dorsodistal margin unarmed; lateral and mesial faces nearly smooth, ventrolateral margin with row of small spines, ventromesial margin smooth, but with row of short to long stiff setae; ventral surface with some long setae. Ischium unarmed.

Ambulatory legs ( Figs. 2 View FIGURE 2 C –E, 4 D, E) similar from right to left, moderately long and slender. Dactyli about 0.9 length of propodi, 6.5 –7.0 times longer than height, terminating in large corneous claws; dorsal surfaces each with sparse short setae; lateral and mesial faces each with few short setae, mesial faces unarmed; ventral margins each with 5–9 moderately long corneous spines notably increasing in size distally. Propodi not tapering distally, slightly to somewhat curved, about 5.0 times longer than distal height; dorsal surfaces each with sparse short setae; lateral faces smooth; ventral margins each with row of 5–9 short corneous spinules, ventrodistal margins each with paired corneous spines. Carpi distinctly shorter than propodi; dorsal surfaces usually with small dorsodistal spine and few short setae; lateral faces smooth. Meri each with short sparse setae on smooth dorsal surface; lateral surfaces nearly smooth; ventrolateral distal margins each with small subdistal spine (second) or unarmed (third), ventral surfaces nearly smooth.

Fourth pereopods ( Fig. 2 View FIGURE 2 F) weakly semichelate, similar from right to left; propodi each with single row of corneous scales.

Anterior lobe of sixth thoracic sternite ( Fig. 2 View FIGURE 2 G, I) subrectangular, anterolateral angles rounded, anterior margin with row of moderately short setae. Eighth thoracic sternite ( Fig. 2 View FIGURE 2 H) composed of two slightly unequal (right larger than left), closely set, rounded lobes.

Male with coxae of fifth pereopods slightly dissimilar ( Fig. 2 View FIGURE 2 H). Right coxa with clearly demarcated, short protrusion at posteromesial part; long setae comprising tuft arising from posteroventral surface of protrusion, directed toward left; papilla­like sexual tube present. Left coxa also with small gonopore partially masked by tuft of short setae directed ventrally. Female with unpaired left gonopore ( Fig. 2 View FIGURE 2 I).

Male with 3 unpaired, unequally biramous left pleopods, female lacking paired pleopods, but with 4 unpaired left pleopods, second and third subequally biramous, fourth and fifth unequally biramous.

Telson ( Fig. 2 View FIGURE 2 J) with shallow or obsolete transverse indentations; terminal margins of posterior lobes horizontal, minutely denticulate, left posterior lobe with lateral margin forming thin, chitinous plate.

Coloration in life. See Fig. 1 View FIGURE 1 . Shield pink or white, with darker patches proximal to bases of ocular peduncles; posterior carapace also pink or white. Ocular peduncles mottled with brown and gray. Antennular peduncle with brown ultimate segment; second segment generally darker brown, with gray narrow band distally; basal segment reddish or pinkish; flagella brown. Antennal peduncle with fifth segment generally transparent, but with brown longitudinal stripes on lateral and mesial margins; third segment with brown middle band on transparent background; second and first segments entirely brown; acicle banded by brown, distal 0.2 and proximal 0.3 white; flagellum entirely pale brown. Right chela entirely pink or light pink with white dactylus and fixed finger; carpus pink, spines on dorsomesial face occasionally darker; merus generally pink or grayish white, with narrow brown transverse band subdistally and large blotch of brown on dorsal surface. Left cheliped generally brown; fingers of chela darker; spines on dorsolateral margin of carpus occasionally darker; merus with brown transverse band subdistally. Ambulatory legs with dactyli brown; propodi white in distal 0.2–0.3, brown in 0.7–0.8, proximodorsal part again white; carpus white or grayish white in distal 0.3, brown in proximal 0.7; meri white or grayish white, with 2 brown transverse bands (1 subdistal and 1 proximal, subdistal one much narrower than proximal one). Fourth pereopods generally transparent, with scattered red chromatophores. Abdomen transparent, with sparse red chromatophores.

Distribution and habitat. Presently known only from Kashiwa­jima Islet, Shikoku and Izu Islands, Japan; rocky reef, 3– 45 m. Using gastropod shells.

Etymology. From the Latin fasciatus   , meaning “banded”, alluding to the banded color pattern of the ambulatory legs.

Remarks. McLaughlin & Haig (1984) divided Pagurixus   into two groups on the basis of presence or absence of two distinct rows of setae on the ventral surface of the ultimate segment of the antennular peduncle. Pagurixus fasciatus   , n. sp. has few very short setae on the ventral surface of the ultimate peduncular segment and falls into the group lacking two distinct rows. Pagurixus fasciatus   most closely resembles P. handrecki   from southern Australia, sharing with it the sharply delimited dorsomesial margin of the right palm. Other species referable to this group include P. a m s a Morgan, 1993, P. a n c e p s ( Forest, 1954), P. granulimanus Morgan, 1993   , P. hectori ( Filhol, 1883)   , P. jerviensis McLaughlin & Haig, 1984   , P. kermadecensis   de Saint Laurent & McLaughlin, 2000, and P. laevimanus ( Ortmann, 1892)   . All have a rounded mesial surface of the right palm ( McLaughlin & Haig 1984, Morgan 1993, de Saint Laurent & McLaughlin 2000, personal observation). Comparison with the original description of P. handrecki   reveals differences in morphology and coloration. The antennal acicle of P. fasciatus   is provided only with a few very short setae on the mesial margin, rather than having a row of tufts of long setae as in P. handrecki   . The mesial margin of the right palm is sharply carinate along the entire length in P. fasciatus   , while only the proximal two thirds to three­quarters is ridged in P. handrecki   . The dorsomesial margin of the carpus of the male right cheliped is only faintly delimited and armed with three or four small spines in P. fasciatus   , rather than distinctly delimited with several large spines arranged in a single or double row as in P. handrecki   . The ventral spines on the ambulatory dactyli appear fewer in P. fasciatus   than in P. handrecki   (5–9, usually 6–8 versus eight 8–14), although the ranges of variation partially overlap. The ornamentation of the left cheliped of females is also different between the two. In P. f a s ­ ciatus, the dorsomesial margin of the palm is delimited by a sharp, tuberculate carina; the dorsolateral margin of the palm is defined by a sharp, smooth carina; the dorsal surface of the palm is only slightly convex; the carpus is devoid of spines on the dorsolateral surface. In P. handrecki   , the dorsomesial margin of the palm is defined by a row or rows of spines or spinulose tubercles; the dorsolateral margin of the palm is also defined by a row of small spines; the dorsal surface has a longitudinal ridge along the midline, often bearing spines or tubercles; the carpus is armed with spines on the dorsolateral surface. The color of P. fasciatus   is distinctly different from P. handrecki   . For example, the ocular peduncles are mottled with brown and gray or white in P. fasciatus   , rather than having some reddish brown longitudinal stripes in P. handrecki   ; the propodi of the ambulatory legs are brown with a white distal band in P. fasciatus   , but they have reddish brown longitudinal stripes in P. handrecki   .

Pagurixus stenops   also shares with the new species the distinctly delimited dorsomesial margin of the right palm, but it is distinctive in the genus in having notably elongate ocular peduncles, being subequal in length to the shield. It further differs from P. fasciatus   in the more elongate right palm in males, which bears a spinulose dorsomesial ridge, and more numerous ventral spines on the ambulatory dactyli (12–15 versus 5–9).

Six species of Pagurixus   are now known from Japanese waters: P. laevimanus   , P. boninensis   , P. maorus   , P. n o m u r a i, and P. fasciatus   n. sp. (see McLaughlin & Haig 1984, Komai & Asakura 1995). In spite of the review by McLaughlin & Haig (1984), the taxonomy of the genus needs further attention because the specific identities of some other species, i.e., P. laevimanus ( Ortmann, 1892)   , P. boninensis ( Melin, 1939)   , P. anceps ( Forest, 1954)   , and P. tweediei ( Forest, 1956)   , remain to be established by examination of the type material. From personal experience, species of the genus are rather common in shallow coral reefs, but the small size of the animals and their cryptic habitats prevent easy collection. Future collections may eventually reveal the existence of many undescribed forms in the Indo­West Pacific region.