Pagurixus brachydactylus, Komai & Osawa, 2006

Komai, Tomoyuki & Osawa, Masayuki, 2006, A review of the Pagurixus boninensis species group, with descriptions of six new species (Crustacea: Decapoda: Anomura: Paguridae), Zootaxa 1214 (1), pp. 1-107 : 64-71

Pagurixus brachydactylus n. sp.

( Figs. 26–28 , 45C, D , 48 )

Pagurixus boninensis .— Ooishi, 1970: 90, pl. 12: fig. 13. Not Pagurixus boninensis ( Melin, 1939) .

Type material

HOLOTYPE: KMNH­Iv 000,021, male (SL 2.4 mm), Minami­saki , Chichi­jima Island, Ogasawara Islands, 3 m, on Pocillopora verrucosa , 7 August 1968, coll. S. Ooishi.

PARATYPES: KMNH­Iv 000,022, 1 male (SL 2.2 mm), same data as holotype ; KMNH­Iv 000,023, 1 female (SL 2.3 mm), same data as holotype ; CBM­ZC 8478, 1 male (SL 2.4 mm), Higashi Port, Haha­jima Island , subtidal, coll. M. Osawa, 19 October 1998 .

Description

Shield ( Fig. 26A ) 1.0–1.1 times as long as broad; anterior margin between rostrum and lateral projections slightly concave; anterolateral margins sloping; dorsal surface with few tufts of short setae laterally. Rostrum triangular, reaching midlength of ocular acicles, moderately slender, terminating acutely. Lateral projections only slightly produced, with submarginal spinule.

Ocular peduncle ( Fig. 26A ) moderately long and stout, 0.6–0.7 length of shield, each with row of tufts of short setae on dorsal surface mesially; corneas not dilated, corneal width 0.3–0.4 of peduncular length; basal part slightly broader than corneal width. Ocular acicles subovate or subtriangular, with small submarginal spine.

Antennular peduncle ( Fig. 26A, B ) overreaching distal margin of cornea by 0.1–0.2 length of ultimate segment. Ultimate segment with tufts of long setae at dorsolateral angle; 2 longitudinal rows of setae on ventral surface, each consisting of mixture of dense short setae and tufts of longer setae directed ventrolaterally ( Fig. 26C ). Basal segment with small lateral spine on statocyst lobe. Ventral flagellum with numerous long setae on lateral and ventral margins.

Antennal peduncle ( Fig. 26A ) just reaching or slightly overreaching distal margin of cornea. Second segment with small spine at dorsomesial distal angle; laterodistal projection short, not reaching midlength of fourth segment. First segment with small laterodistal spine; ventromesial distal margin produced, unarmed or with spinule just lateral to antennal gland opening. Antennal acicle short, arcuate, reaching base of cornea; mesial margin with row of short stiff setae. Flagellum relatively short, exceeding 2.0 length of shield.

Right cheliped of males ( Fig. 27A–C ) not particularly elongate, stout. Chela subovate in dorsal view, 1.5–1.7 times longer than broad. Dactylus 0.6–0.7 length of palm; dorsomesial margin not delimited; surfaces covered with coarse granules; cutting edge with 4 or 5 low calcareous teeth, terminating in small calcareous claw. Palm slightly longer than carpus; convex dorsal surface covered with coarse granules, dorsolateral and dorsomesial margins not delimited; lateral, mesial and ventral surfaces granular, with few tufts of short setae on ventral surface. Cutting edge of fixed finger with 1 or 2 low calcareous teeth, terminating in calcareous claw. Carpus slightly longer than merus; dorsolateral and dorsomesial margins not delimited; all surfaces coarsely granular (granules occasionally arranged in short to long transverse rows), lateral surface lacking median ridge. Meral­carpal articulation lacking any pronounced clockwise rotation; dorsal surface of merus with few low transverse ridges distally, otherwise almost smooth, and with few tufts of setae, dorsodistal margin with row of short bristles, but without spines; lateral face with low, rounded protuberances in ventral half, otherwise nearly smooth, ventrolateral margin with row of moderately small spines in distal half; mesial face nearly smooth, with scattered long stiff setae, ventromesial margin with row of rounded tubercles; ventral faces with scattered small tubercles and long setae. Ischium with row of small denticles on ventromesial margin, otherwise unarmed.

Right cheliped of female missing.

Left cheliped ( Fig. 27D–G ) moderately slender, similar between males and female. Chela 2.2–2.5 times longer than broad. Dactylus slightly longer than palm, with sparse tufts of setae on surfaces (setae on ventral surface longest); dorsal surface unarmed; cutting edge with row of small corneous teeth, terminating in small corneous claw. Palm about half length of carpus; dorsal surface weakly elevated in mid­line and bearing scattered very small tubercles, dorsolateral margin faintly delimited by row of small tubercles, dorsomesial margins not delimited; lateral, mesial and ventral surfaces with small tubercles or low protuberances; scattered long setae present on mesial and ventral surfaces. Cutting edge of fixed finger with row of small corneous teeth. Carpus moderately stout, somewhat compressed laterally, 0.8–0.9 length of chela and slightly shorter than merus; length 2.1–2.3 of distal width and 1.8–2.0 of greatest height; dorsolateral and dorsomesial margins each with row of low, small protuberances and short bristles, but no conspicuous spines present; surfaces with few very small tubercles or granules; sparse long setae on mesial and ventral surfaces; lateral surface lacking median longitudinal ridge, thus nearly perpendicular. Merus with 1 subdistal transverse ridge extending onto lateral and mesial surfaces, otherwise nearly smooth, dorsodistal margin with row of short stiff setae; lateral surface with scattered, very small low protuberances, ventrolateral margin with row of moderately small spines; mesial face nearly smooth, ventromesial margin faintly granular and with row of short to long bristles or stiff setae; ventral surface weakly convex, with few small low tubercles and long stiff setae. Ischium with row of tiny denticles on ventromesial margin, otherwise unarmed.

Ambulatory legs ( Fig. 28A, B ) relatively short, stout, similar from right to left. Dactyli ( Fig. 28C, D ) 0.5–0.8 length of propodi, 3.0–3.7 times longer than high, terminating in large corneous claws; dorsal surfaces each with row of sparse short setae; lateral and mesial faces faintly sulcate medially, each with few tufts of short setae, mesial faces unarmed; ventral margins each with 3–6 moderately long corneous spines notably increasing in size distally. Propodi not tapering distally, 3.2–4.0 times longer than high; dorsal surfaces each with row of low protuberances and short stiff setae or bristles; lateral faces smooth or with scattered very low protuberances; ventral margins each with 1–3 corneous spinules, ventrodistal margins each with paired corneous spines. Carpi each with small dorsodistal spine, dorsal surfaces nearly smooth, but with row of short bristles; lateral faces with sparse granules and few short bristles. Meri each with moderately long setae and short bristles on nearly smooth dorsal surface; lateral surfaces nearly smooth; ventrolateral distal margins each with small subdistal spine (second) or unarmed (third), ventral surfaces with row of low protuberances (second) or smooth (third), all with sparse short to moderately long setae.

Fourth pereopods generally similar from right to left in males ( Fig. 26D–G ), markedly unequal with left larger in female ( Fig. 26H–K ). Dactyli terminating in small corneous claws, with long setae on dorsal margins (setae longer and more numerous in female than in male). Propodi of males each with tuft of several setae on nearly flat mesial face at base of fixed finger. Left propodus of female with prominent tuft of long setae on weakly convex mesial face at base of ventrodistal extremity, right propodus with tuft of some shorter setae on flat mesial face at base of ventrodistal extremity. Left carpus of female with prominent tuft of long setae at ventrodistal angle on mesial face.

Anterior lobe of sixth thoracic sternite ( Fig. 26L ) subrectangular, anterolateral angles rounded, anterior margin with row of moderately short setae. Eighth thoracic sternite ( Fig. 26M ) composed of two unequal, narrowly separated, rounded lobes (right lobe larger than left).

Males with slightly unequal coxae of fifth pereopods ( Fig. 26M ). Right coxa with tuft of numerous long stiff setae directed toward left and passing across left coxa; ventromesial protrusion absent, but papilla­like very short sexual tube or protrusion of vas deferens occasionally present. Left coxa also with gonopore partially masked by tuft of setae directed ventrally. Female with unpaired left gonopore.

Telson ( Fig. 26N ) with terminal margins oblique, minutely denticulate or with 4 or 5 very small spinules.

Colour in life. ( Fig. 45 C, D ) Shield generally white. Ocular peduncles pale brown, becoming darker distally. Right cheliped generally pale brownish purple; carpus with brownish purple blotches. Left cheliped white in ground color; chela, carpi and meri with brownish purple blotches. Ambulatory legs generally white, with brownish purple markings; dactyli each with blotch on proximal part, extending along midline toward base of claw on lateral face and along dorsal face; propodi each with broad band in proximal half, spotted by white; carpi each with irregular blotch on dorsolateral surface; meri each with 2 blotches on dorsal surface.

Colour in preservative. Color mostly faded away, but orange markings on ambulatory legs still evident. Dactyli each with blotch on proximal part, extending along midline toward base of claw on lateral face; propodi white in distal half and orange in proximal half, latter occasionally interrupted by white blotch on dorsal surface; carpi with 2 orange blotches dorsally, connected by median stripe on lateral surface; meri each with orange blotch on dorsal surface distally.

Distribution So far known only from the Ogasawara Islands ( Fig. 48 ); intertidal to 3 m. Remarks

Among the seven species of the subgroup B of the P. boninensis group, P. brachydactylus n. sp. most closely resembles P. pseliophorus n. sp. These two species share short and stout dactyli of the ambulatory legs and the absence of conspicuous spines on the dorsal surface of the carpus of the male right cheliped. Morphological differences between the two species are summarized in Table 2. The shape of the shield, structure of the setal series on the ultimate segment of the antennular peduncle, armament of the carpus of the left cheliped, and structure of the coxa of right fifth pereopod in males are useful for species discrimination. The coloration in life is also different between the two species. For example, the propodi of the ambulatory legs are white in the distal half and purplish brown in the proximal half in P. brachydactylus , while they have middle dark brown bands in P. pseliophorus .

As mentioned before, reexamination of the specimens from the Ogasawara Islands, reported by Ooishi (1970), has shown that they do not represent P. boninensis s. s., but P. brachydactylus n. sp.

Etymology

From the Greek brachys, meaning ’short’, and dactylos, meaning “claw”, in reference to the short dactyli of the ambulatory legs.

Figures

FIGURE 26. Pagurixus brachydactylus n. sp. A–G, L–N, holotype male (SL 2.4 mm) from Chichijima Island, Ogasawara Islands (KMNH­Iv 000,021); H–K, paratype female (SL 2.3 mm) from same locality (KMNH­Iv 000,023). A, shield and cephalic appendages, dorsal view; B, left antennule, lateral view; C, ultimate segment and ventral flagellum of antennule, ventral view; D, H, left fourth pereopod, dactylus and propodus, lateral view; E, I, same, mesial view; F, J, right fourth pereopod, dactylus and propodus, lateral view; G, K, same, mesial view; L, sixth thoracic sternite, ventral view; M, coxae of fifth pereopods and eighth thoracic sternite, ventral view; N, telson, dorsal view. Scale bars: 1 mm for A; 0.5 mm for B–N.

FIGURE 27. Pagurixus brachydactylus n. sp. Holotype male (SL 2.4 mm) from Chichi­jima Island, Ogasawara Islands (KMNH­Iv 000,021). A, right cheliped, chela and carpus, dorsal view; B, entire right cheliped, mesial view; C, same, lateral view; D, left cheliped, chela, dorsal view; E, entire left cheliped, mesial view; F, same, lateral view; G, left cheliped, carpus, dorsal view. Scale bar: 1 mm.

FIGURE 28. Pagurixus brachydactylus n. sp. Holotype male (SL 2.4 mm) from Chichi­jima Island, Ogasawara Islands (KMNH­Iv 000,021). A, right second pereopod, lateral view; B, left third pereopod, lateral view; C, right second pereopod, dactylus and distal part of propodus, mesial view; D, left third pereopod, dactylus and distal part of propodus, mesial view. Scale bar: 0.5 mm.

FIGURE 45. A, Pagurixus boninensis (Melin, 1939), ovigerous female (SL 2.7 mm) from Hachijo Island, Izu Islands, Japan (CMNH­ZC 1688), photo taken by J. Okuno; B, Pagurixus carinimanus n. sp., paratype female (SL 1.6 mm) from Okinawa Island, Ryukyu Islands (CBM­ZC 8481), photo taken by Y. Fujita; C, D, Pagurixus brachydactylus n. sp., male (SL 2.6 mm) from Chichi­jima Island, Ogasawara Islands, photo taken by M. Osawa.

FIGURE 48. Geographic distribution of Pagurixus boninensis (), P. festinus (), P. brachydactylus n. sp. (), P. carinimanus n. sp. (), P. paulayi n. sp. (Π), P. pseliophorus n. sp ()., and P. ruber n. sp. ().