Pagurixus longipes

Osawa, Masayuki, Fujita, Yoshihisa & Okuno, Junji, 2006, Two new species of Pagurixus (Crustacea: Decapoda: Anomura: Paguridae) from submarine caves of the Ryukyu Islands, southwestern Japan, Zootaxa 1148, pp. 27-45 : 36-44

Pagurixus longipes n. sp ( Figs. 4–6 , 7 C)

[new Japanse name: Ashinaga­hime­hon­yadokari]

Type material. HOLOTYPE: CMNH­ZC 638, male (SL 2.4 mm), "Deep Kiss Drop", Kume­jima Island, Ryukyu Islands, submarine cave, 35 m, 21 December 2001, coll. A. Shioiri and J. Okuno.

Description. Eleven pairs of biserial phyllobranchiae.

Shield ( Fig. 4 A) approximately as long as broad; anterior margin between rostrum and lateral projections concave; anterolateral margins slightly terraced; posterior margin truncate; dorsal surface with several pairs of tufts of short setae. Rostrum triangular, distinctly overreaching lateral projections and reaching 0.3 length of ocular acicles, terminating in small spine. Lateral projections obtusely triangular, with small submarginal spine.

Ocular peduncles ( Fig. 4 A) stout, approximately 0.5 length of shield, each with row of tufts of short setae on dorsal surface mesially; corneas dilated, corneal width about 0.4 of peduncular length; basal part inflated, as broad as corneas. Ocular acicles subovate, with small submarginal spine, separated basally by basal width of 1 acicle; mesial margin with few short setae.

Antennular peduncle ( Fig. 4 A, D) overreaching distal margin of cornea by full length of ultimate segment. Ultimate segment with 3 or 4 short and long setae at dorsolateral distal angle; ventral surface with several very short setae but lacking 2 rows of setal tufts or longitudinal setal bands. Basal segment with small spine on lateral face of statocyst lobe.

Antennal peduncle ( Fig. 4 A) overreaching distal margin of cornea by nearly full length of fifth segment. Fifth and fourth segments with few setae. Third segment apparently unarmed but with tuft of short setae at ventromesial distal angle. Second segment with small spine at dorsomesial distal angle; dorsolateral distal projection moderately elongate, not reaching midlength of fourth segment, terminating in bifid spine. First segment unarmed at distolateral angle; ventromesial distal margin produced, slightly serrated lateral to antennal gland opening. Antennal acicle moderately long, arcuate, distinctly overreaching distal margin of cornea; mesial margin with row of tufts of setae. Flagellum extremely long, approximately 10.0 length of shield.

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 midlength of carpus.

Right cheliped ( Fig. 5 A–D) greatly elongate. Chela subovate in dorsal view, approximately 3.3 times longer than wide measured along base of fingers. Dactylus 0.5 length of palm, moderately curved ventrally; surfaces closely granular, with scattered tufts of setae; dorsal surface with rounded longitudinal, short ridge proximally and short, slightly elevated longitudinal ridge of small granules distally; dorsomesial margin weakly delimited by ridge of small granules; cutting edge with 1 prominent calcareous tooth medially and small calcareous teeth on proximal 0.8 and row of small, closely set corneous teeth in distal 0.2, terminating in small corneous claw. Palm approximately as long as carpus; convex dorsal surface covered with numerous granules, dorsolateral margin delimited by granular ridge on distal part and fixed finger but obsolete on median part except short proximal crest, dorsomesial margin not delimited; lateral, mesial and ventral surfaces with numerous small granules and scattered short and moderately long setae, ventral face convex. Cutting edge of fixed finger with 2 low but prominent teeth proximal 0.7 and row of partially fused small calcareous teeth on distal 0.3, terminating in small corneous claw. Carpus 1.1 times as long as merus, length approximately 2.2 of distal width and 2.5 of greatest height; dorsolateral margin weakly delimited by row of small subacute protuberances; dorsomesial margin weakly delimited by irregular row of spines (proximal 0.3 margin crested), strongest on proximal half; all surfaces with numerous small granules, lateral surface divided in oblique dorsal and perpendicular ventral sections by distinct, longitudinal ridge of small tubercles. Merus with row of low transverse ridges bearing short stiff setae on dorsal surface; dorsodistal margin with small mesial spine and row of short stiff setae; lateral surface with small, flattened granules; mesial surface with short vertical ridges; ventrolateral margin with 3 distal spines; ventromesial margin with 2 distal spines; ventral surface flattish, covered with small granules. Ischium with row of small, subacute tubercles on ventrolateral and ventromesial margins.

Left cheliped ( Fig. 5 E–H) elongate, very slender. Chela 4.6 times longer than broad measured along base of fingers. Dactylus 1.2 times longer than palm, with sparse tufts of setae on surfaces; surfaces nearly smooth; cutting edge with fine row of small corneous teeth, terminating in small corneous claw. Palm 0.4 length of carpus; dorsal surface slightly convex, with sparse, small granules and denticles, dorsolateral margin delimited by row of small protuberances; dorsomesial margin proximally delimited by row of small protuberances; mesial and ventral surfaces with small flattened granules and sparse tufts of moderately long setae. Cutting edge of fixed finger with row of rounded corneous teeth, terminating in small corneous claw. Carpus elongate, very slender, subcylindrical, approximately as long as chela, 0.9 length of merus; length approximately 5.5 of distal width and 5.2 of greatest height; surfaces with small granules, very short low ridge, and scattered, short and long setae; dorsolateral and dorsomesial margins each with row of small protuberances and sparse setae; lateral surface divided in oblique dorsal section and perpendicular ventral section by distinct, longitudinal ridge of small granules and protuberances; mesial and ventral surfaces with sparse moderately long setae. Merus with row of short transverse ridges on dorsal surface; dorsodistal margin unarmed but with row of short stiff setae; lateral surface with numerous, very short vertical ridges and few short setae, ventrolateral margin with 2 small subdistal spines; mesial face with short vertical ridges and sparse short setae, ventromesial margin with 1 small subdistal spine; ventral surface slightly concave, with scattered small granules. Ischium with row of small granules on ventromesial margin, otherwise apparently unarmed.

Ambulatory pereopods ( Fig. 6 A–F) long and very slender, generally similar from right to left; lateral and mesial surfaces of propodus to merus with flattened granules, most numerous on meri. Dactyli weakly curved ventrally and mesially, 1.0–1.2 length of propodi (measured along dorsal surface, excluding distal rounded projection), 12.0–14.4 times longer than proximal height, terminating in large corneous claws; dorsal surfaces each with row of sparse, short and long setae, distal part with row of dense short setae; lateral and mesial faces with few tufts of short setae near dorsal and ventral margins, mesial faces unarmed in second but with row of corneous spinules adjacent to dorsal margin in third; ventral margins each with 9 or 10 slender corneous spines increasing in size distally. Propodi tapering distally, not curved, 6.4–7.4 times longer than distal height; dorsal surfaces each with row of short, low, transverse ridges bearing short and moderately long setae; lateral and mesial surfaces with few short setae; ventral surface slightly protuberant, each with row of 4 or 5 small, slender corneous spines, ventrodistal margins each with paired long corneous spines. Carpi with low protuberances and sparse setae dorsally; dorsodistal margins unarmed. Meri somewhat tapering distally; dorsal surfaces each with irregular row of short, low, transverse ridges bearing few short stiff setae; ventral margins minutely crenulated, with row sparse short setae; ventrolateral distal margins each with small denticles or protuberances and small subdistal spine on second, but only with small, low protuberances on third.

Fourth pereopods missing. Coxae equal in size.

Coxae of fifth pereopods ( Fig. 4 E) slightly unequal, right larger than left; right coxa with clearly demarcated, short posteromesial protrusion; long setae comprising tuft arising from posteroventral surface of protrusion, directed toward left and nearly reaching left coxa; sexual tube short; left coxa with papilla­like sexual tube masked by tuft of moderately long setae directed ventrally.

Third thoracic sternite with pair of small spines on anterior median margin. Anterior lobe of sixth thoracic sternite ( Fig. 4 B) transversely subrectangular, anterolateral angles rounded, anterior margin with row of moderately long setae. Eighth thoracic sternite composed of 2 subequal, closely set, rounded lobes.

Abdomen with 3 unpaired, unequally biramous left pleopods.

Telson ( Fig. 4 C) with transverse indentations; posterior lobes subequal in size, terminal margins oblique, with few blunt, very small spines; chitinous plates present along terminal margins.

Coloration. See Fig. 7 C. Shield generally white but reddish brown marginally. Ocular peduncles pale reddish brown. Antennular peduncles brown. Antennal peduncles pale brown; fifth segment with brown lateral and mesial stripes. Right cheliped generally pale brown, without distinct markings. Left cheliped semitransparent, reddish brown; distal part of dactylus and fixed finger white. Ambulatory pereopods also semitransparent, reddish brown; no distinct markings.

Etymology. The specific name is the combination of the Latin, longus (long) and pes (leg), in reference to the elongate chelipeds and ambulatory pereopods.

Remarks. Although the sole specimen lacks both the fourth pereopods, the assignment of the new species to Pagurixus is justified because of the presence of the distinct tuft of stiff setae directed toward left on the coxa of the male right fifth pereopod, a unique feature of the genus.

Pagurixus longipes n. sp. has only several very short setae on the ventral surface of the ultimate segment of the antennular peduncle and falls into the P. anceps group characterized by the absence of two distinct, longitudinal rows or series of setae on the segment (see Remarks of P. pulcher n. sp.). Pagurixus longipes , however, clearly differs from other species of the P. anceps group by having the very elongate chelipeds and ambulatory pereopods, especially the long and slender, carpus of the left cheliped and dactyli of the ambulatory pereopods. The new species is further distinguished from those species except for P. hectori ( Filhol, 1883) by the lack of the conspicuous spines on the dorsolateral and dorsomesial margins of the carpus of the left cheliped. Pagurixus hectori is described as possessing a row of small spines or short transverse denticulate ridges on each the margins (de Saint Laurent & McLaughlin 2000). Pagurixus longipes is immediately differentiated from P. hectori by the length of the antennular and antennal peduncles and the absense of the elevated ridge with irregular double row of small, blunt or acute tubercles on the dorsal midline of the left palm, and markedly elongate, slender chelipeds and ambulatory pereopods. The antennular peduncle is distinctly longer in P. longipes than in P. hectori . It overreaches the distal margin of the cornea by the full length of the ultimate segment in P. longipes , rather than only by 0.35–0.60 length of the ultimate segment in P. hectori . The antennal peduncle also overreaches the distal margin of cornea by nearly the full length of the fifth segment in P. longipes , in comparison to 0.25–0.50 length of the fifth segment in P. hectori .

The new species superficially resembles P. nomurai belonging to the P. boninensis group,the different informal species group of the genus (see Remarks of P. p u l c h e r n. sp.). These two species share the very elongate chelipeds and ambulatory pereopods, a tuberculate longitudinal ridge on the lateral surface of the carpus of the male right cheliped, no conspicuous spines on the dorsolateral and dorsomesial margins of the carpus of the left cheliped, and weak armature on the terminal margins of the telson. Pagurixus nomurai has been also recorded from submarine caves in the Ryukyu Islands ( Osawa & Takeda 2004). Pagurixus longipes , however, differs from P. nomurai by the proportionally longer antennular and antennal peduncles, more slender dactyli of the ambulatory pereopods, and the shape of the anterior lobe of the sixth thoracic sternite. The antennular peduncle overreaches the distal margin of the cornea by the full length of the ultimate segment in P. longipes , in comparison to 0.2–0.3 length of the ultimate segment in P. nomurai . The antennal peduncle also overreaches the distal margin of the cornea by nearly the full length of the fifth segment in P. longipes , instead of 0.3 length of the fifth segment in P. nomurai . The dactyli of the ambulatory pereopods are 12.0–14.4 times longer than the proximal height in P. longipes , whereas they are 8.6–11.8 times longer in P. nomurai .

The anterior lobe of the sixth thoracic sternite is transversely subrectangular in P. longipes and P. nomurai . In P. longipes , however, the anterior and posterior margins are subequal in length and the anterolateral angles are rounded. In P. nomurai , the anterior margin is longer than the posterior margin and the anterolateral angles bear a narrow ridge directed laterally at least in female. The live coloration of P. longipes and P. nomurai is also different. The chelipeds and ambulatory pereopods of P. longipes are entirely pale brown or semitransparent reddish brown, without conspicuous markings, whereas those of P. nomurai are generally brown, olive or bluish gray, with a moderately broad white band each on the meri.

The possession of a tuberculate longitudinal ridge on the lateral surface of the carpus of the left cheliped has been known in P. maorus and P. nomurai as well as P. longipes . This character is also found in P. laevimanus ( Ortmann, 1892) , P. tweediei ( Forest, 1956) , and an undescribed species of the genus (Komai & Osawa, in preparation). All of the aforementioned species, except for P. longipes , have two distinct, longitudinal rows or tufts of setae on the ventral surface of the antennular ultimate segment. The possession of setal rows or tufts on the antennular ultimate segment appears to be an apomorphic character based on preliminary comparison with other pagurid genera (personal observation). The lack of the setal rows or tufts in P. longipes shows that the presence of a tuberculate ridge on the lateral surface of the carpus of the left cheliped possibly does not represent a feature uniting P. longipes with the other five species mentioned above.

Figures

FIGURE 4. Pagurixus longipes, n. sp. Holotype male, SL 2.4 mm, CMNH­ZC 638. A, shield and cephalic appendages, dorsal view (omitted setae from right side); B, sixth thoracic sternite, ventral view; C, telson, dorsal view; D, left antennule, ultimate segment, lateral view; E, coxae of fifth pereopods and eighth thoracic sternite, ventral view. Scales equal 1.0 mm.

FIGURE 5. Pagurixus longipes n. sp. Holotype male, SL 2.4 mm, CMNH­ZC 638. A, right cheliped, lateral view; B, same, mesial view; C, chela, dorsal view (omitted setae); D, carpus, dorsal view (omitted setae); E, left cheliped, lateral view; F, same, mesial view; G, same, chela, dorsal view (omitted setae); H, same, carpus, dorsal view (omitted setae). Scales equal 1.0 mm.

FIGURE 6. Pagurixus longipes n. sp. Holotype male, SL 2.4 mm, CMNH­ZC 638. A, right second pereopod, lateral view; B, same, dactylus, mesial view; C, left third pereopod, lateral view; D, same, dactylus, mesial view; E, right third pereopod, lateral view; F, same, dactylus, mesial view. Scales equal 1.0 mm.

FIGURE 7. Entire animal. A, Pagurixus pulcher n. sp., holotype female, SL 2.4 mm, CMNH­ZC 783; dorsal view, B, Pagurixus pulcher n. sp., paratype male, SL 2.7 mm, CMNH­ZC 1820, anterior view; C, Pagurixus longipes n. sp., holotype male, SL 2.4 mm, CMNH­ZC 638, dorsal view.