Pagurixus formosus, Komai, 2010

Komai, Tomoyuki, 2010, New species and new records of the hermit crab genus Pagurixus Melin, 1939 (Crustacea: Decapoda: Anomura: Paguridae) from the Indo-West Pacific, Journal of Natural History 44 (21 - 22), pp. 1269-1342 : 1306-1313

Pagurixus formosus sp. nov.

( Figures 17–19 )

Material examined

Holotype. Shiangianwan , Kenting, Pingtung County, southern Taiwan, 3–8 m, fore reef of near shore fringing reef, under rocks, 29 October 2000, coll. G. Paulay, male SL 2.9 mm ( FMNH 5179 ).

Paratypes. Shadau , Kenting, Pingtung County, southern Taiwan, 2–7 m, forereef of nearshore fringing reef, under rocks, 30 October 2000, 1 female SL 1.6 mm, 1 ovigerous

female SL 2.3 mm ( FMNH 3771 ); same data as holotype, 1 male SL 2.4 mm, 1 ovigerous female SL 3.0 mm ( FMNH 5179 b) .

Description

Shield ( Figure 17A ) as long as broad; anterior margin between rostrum and lateral projections concave; anterolateral margins sloping; dorsal surface convex, with few tufts of short setae laterally. Rostrum moderately broadly triangular, reaching level of midlength of ocular acicles, terminating acutely. Lateral projections obtusely triangular, without marginal or submarginal spinule.

Ocular peduncles ( Figure 17A ) relatively stout, about 0.6 length of shield, each with row of tufts of short stiff setae on dorsal surface mesially (setae at base of cornea very short); corneas not dilated, corneal width about 0.4 of peduncular length; basal part slightly inflated, as broad as cornea. Ocular acicles subtriangular, each with submarginal spinule.

Antennular peduncles ( Figure 17A ) slightly overreaching distal corneal margins. Ultimate segment with tuft of long setae on dorsolateral distal portion; ventral surface with two longitudinal bands of setae extending distally onto proximal two articles of ventral flagellum, each band consisting of irregularly arranged short setae (setae directed outward to posteriorly) ( Figure 16B ). Basal segment with small laterodistal spine on statocyst lobe. Ventral flagellum ( Figure 17B ) with thick long setae on lateral and mesial margins.

Antennal peduncles ( Figure 17A ) overreaching distal corneal margins by half length of fifth segments. Third segment with small spine at ventromesial distal angle, practically obscured by tuft of stiff setae. Second segment with spinule at dorsomesial distal angle; laterodistal projection very short, far falling short of midlength of fourth segment, terminating in bifid spine. First segment unarmed on lateral surface; ventromesial distal margin with flattened rounded projection, bearing few spinules anterolaterally. Antennal acicle moderately long, slightly arcuate, nearly reaching distal corneal margin; mesial margin with few very short setae. Flagellum moderately long, exceeding 3.0 length of shield; each article with few very short setae distally.

Male right cheliped ( Figures 18A, B , 19A ) fairly elongate, much larger than left cheliped. Chela about 2.2 times longer than broad; lateral margin slightly sinuous, mesial margin nearly straight. Dactylus about 0.6 times as long as palm, noticeably curved ventrally, terminating in calcareous claw; dorsomesial margin not delimited; surfaces minutely granular; cutting edge with one obtuse calcareous tooth proximal to midlength; some tufts of short setae on ventral surface. Palm somewhat elongate, distinctly longer than carpus; convex dorsal surface minutely granular, without conspicuous spines or tubercles; dorsolateral margin delimited by weak granular ridge extending nearly to tip of fixed finger; dorsomesial margin not delimited; proximomesial part slightly compressed vertically; all surfaces minutely granular, ventral surface with scattered moderately short setae laterally. Fixed finger terminating in calcareous claw; cutting edge with one prominent calcareous tooth at about midlength. Carpus about 1.5 times longer than broad; dorsal surface generally minutely granular, with scattered coarser granules, dorsomesial margin delimited in proximal 0.6 by irregular double row of small spines or spinulose tubercles; dorsolateral margin not delimited; lateral surface with trace of longitudinal ridge dorsally, ventrolateral margin sinuous, unarmed; mesial face with coarse granules adjacent to dorsomesial margin and with few short stiff setae, ventromesial margin unarmed; ventral surface noticeably convex, nearly smooth, with scattered stiff setae. Meral– carpal articulation lacking any pronounced clockwise rotation; dorsal surface of merus with short transverse ridges or low protuberances and short stiff setae, dorsodistal margin with four small spines and short stiff setae; lateral face nearly smooth in most part, but dorsodistal portion roughened with short vertical ridges or low protuberances, ventrolateral margin with one moderately small spines distally; mesial face nearly smooth, with some short to long stiff setae, ventromesial margin with row of small spines in distal half; ventral surface slightly convex with several long setae, particularly numerous on mesial side. Ischium with smooth ventromesial margin; surfaces unarmed, but with short stiff setae.

Female right cheliped ( Figures 18C, D , 19B, C ) somewhat larger than left. Chela subovate, about 1.9 times longer than broad. Dactylus very slightly curved ventrally, subequal in length to palm; dorsomesial margin not delimited; dorsal surface with row of small tubercles extending nearly to midlength; mesial face nearly smooth, with scattered tufts of short setae; ventral surface also with tufts of stiff setae; cutting edge with row of blunt, unequal calcareous teeth in proximal 0.6 and row of small corneous teeth in distal half, terminating in small corneous claw. Palm about 0.7 length of carpus; dorsal surface slightly convex, with coarse granules; dorsolateral margin weakly carinate; dorsomesial margin not delimited; lateral and mesial faces coarsely granular; ventral surface convex. Fixed finger terminating in small calcareous claw, with row of small, rounded calcareous teeth in distal half and faintly dentate in proximal half. Carpus about 1.7 times longer than wide, slightly shorter than chela; dorsal surface sparsely granular, dorsolateral and dorsomesial margins each with row of small spines or spinulose tubercles; lateral surface divided in two sections by longitudinal granular ridge, lower section coarsely granular, ventrolateral margin nearly smooth; mesial surface also coarsely granular, with few short dorsally, ventromesial margin granular; ventral surface moderately convex, nearly naked. Merus with low transverse ridges on dorsal surface, dorsodistal margin with stiff setae; lateral face coarsely granular, ventrolateral margin granular, with one small subdistal spine; mesial face with sparse granules, ventromesial margin granular, without conspicuous spines. Ischium with row of minute denticles on ventromesial margin; surfaces otherwise unarmed.

Left cheliped ( Figure 19D–F ) similar between male and female, moderately slender. Chela about 2.4 times longer than broad. Dactylus subequal in length to palm, with sparse tufts of short setae on surfaces; cutting edge with row of small corneous teeth over entire length, terminating in small corneous claw. Palm about halflength of carpus; dorsal surface weakly convex, with row of tiny tubercles on slightly elevated midline extending onto base of fixed finger, and scattered coarse granules on mesial side, dorsolateral and dorsomesial margins not delimited; lateral face with very low, subsquamiform protuberances and coarse granules; mesial face with coarse granules dorsally, nearly smooth ventrally; ventral surface slightly convex, with small, low protuberances and scattered tufts of short to long setae. Fixed finger terminating in small corneous claw; cutting edge with row of small, subacute calcareous teeth; dorsal surface with scattered short setae. Carpus only slightly compressed laterally, subequal in length to chela or merus; length 2.3 of distal width and 2.7 of greatest height; dorsolateral margin with row of coarse granules or tiny tubercles and short stiff setae, dorsomesial margin with row of larger tubercles and longer setae, dorsodistal margin without conspicuous spines; lateral face faintly divided into slightly oblique dorsal and nearly perpendicular ventral sections, latter coarsely granular, ventrolateral margin faintly granular in distal part; mesial face with scattered low protuberances bearing stiff setae and coarse granules dorsally, nearly smooth ventrally, ventromesial margin unarmed; ventral surface weakly convex, with several long setae. Merus with low transverse ridges on dorsal surface, dorsodistal margin with stiff setae; lateral face with numerous, minute vertical ridges nearly smooth, ventrolateral margin with one tiny distal spine followed by row of small, rounded tubercles; mesial surface with short, obliquely vertical or vertical ridges, and with short to long setae ventrally, ventromesial margin only weakly tuberculate, lacking conspicuous spines; ventral surface weakly convex, with several long stiff setae. Ischium unarmed on laterodistal margin; ventromesial margin with row of minute denticles.

Ambulatory legs ( Figure 17C, E .) moderately long and slender, similar from right to left in general structure. Dactyli ( Figure 17D, F ) 0.7–0.8 length of propodi, 5.9–6.1 times longer than broad, slightly curved ventrally, terminating in strong corneous claws; dorsal surfaces each with sparse tufts of very short setae; lateral surfaces with scattered short setae (second) or only with few short setae (third); mesial faces unarmed (second) or each armed with row of corneous spinules dorsally (third); ventral margins each with seven or eight corneous spines notably increasing in size distally. Propodi slightly tapering distally, 3.7–3.8 times longer than broad; dorsal surfaces with low transverse ridges and sparse short setae; lateral surfaces sparsely granular, nearly naked; ventral margins each with row of four corneous spinules distally, ventrodistal margins each with paired small corneous spines. Carpi each with small dorsodistal spine; dorsal surfaces nearly smooth (second) or with low transverse ridges and sparse short setae (third). Meri each with low transverse ridges and tufts of short setae (second) or nearly smooth on dorsal surface; lateral surfaces sparsely granular (second) or nearly smooth; ventrolateral distal margins each with small subdistal spine (second) or unarmed (third), ventral margins markedly sinuous (second) or generally convex (third), naked (second) or with sparse setae (third).

Fourth pereopods ( Figure 17G ) subequal and similar in both male and female. Dactyli moderately broad, nearly straight, terminating in small corneous claws, without prominent tuft of setae. Propodi each with sparse short stiff setae on dorsal surface, mesial face nearly flat, propodal rasp of single row of corneous scales.

Anterior lobe of sixth thoracic sternite ( Figure 17H ) transversely oblong, with laterally produced anterolateral angles; ventral surface with transverse row of stiff setae anteriorly. Eighth thoracic sternite ( Figure 17I ) composed of two subequal, narrowly separated, rounded lobes.

Coxae of fifth pereopods ( Figure 17I ) unequal. Right coxa with tuft of long stiff setae arising from surface adjacent to gonopore, directed toward left and reaching to left coxa; posteromesial protrusion not developed or no protrusion of vas deferens apparent. Left coxa with gonopore partially masked by stiff setae. Female with paired gonopores.

Telson ( Figure 17J ) with rounded posterior lobes separated by narrow median cleft; terminal margins slightly oblique, each with row of minute spinules.

Colouration

In preservative. Shield, ocular peduncles, and antennae generally pale yellowishbrown, no distinct markings seen. Chelipeds and ambulatory legs generally pale yellowish-brown; meri of chelipeds each with trace of white subdistal and middle transverse bands; meri of ambulatory legs also each with white transverse band subdistally.

Size

Largest male SL 2.9 mm, ovigerous female SL 2.8 mm.

Distribution

So far known only from Kenting, Pingtung County, southern Taiwan, 2–8 m.

Etymology

The new species is named after the country embracing the type locality. Formosa is an old name for Taiwan .

Remarks

Pagurixus formosus sp. nov. closely resembles P. tweediei ( Forest, 1956) particularly in the general shape and armature of the chelipeds and ambulatory legs, and the general setation of the ultimate segment of the antennular peduncle. Nevertheless, the new species can be distinguished from P. tweediei by the presence of dorsolateral and dorsomesial rows on the carpus of the left cheliped, which are composed of tubercles, instead of sharp spines, and the lack of a ventrodistal spine on the merus of the third pereopod. Although colouration in life was not recorded for this new species, available specimens had markings still preserved. The preserved colour pattern clearly suggests that the live colouration is also different between the two species. In P. formosus , the propodi lack conspicuous markings, but in P. tweediei , those segments have distal bands ( Komai and Osawa 2006).

Pagurixus laevimanus , which is represented only by the holotype, is also similar to P. formosus . However, the presence of conspicuous spines on the dorsolateral margin of the carpus of the right cheliped immediately distinguishes P. laevimanus from P. formosus .

Figures

Figure 16. Pagurixus crosnieri sp. nov. holotype, male (shield length 3.0 mm; MNHN-Pg 8311). (A) Right second pereopod, lateral view; (B) Right second pereopod, dactylus, mesial view; (C) left third pereopod, lateral view; (D) left third pereopod, dactylus, mesial view. Note: Scale bars, 1 mm.

Figure 17. Pagurixus formosus sp. nov. holotype, male (shield length 2.9 mm; FMNH 5179). (A) Shield and cephalic appendages, dorsal view; (B) ultimate segment and ventral flagellum of left antennule, ventral view; (C) right second pereopod, lateral view; (D) right second pereopod, dactylus, mesial view; (E) left third pereopod, lateral view; (F) left third pereopod, dactylus, mesial view; (G) distal three segments of left fourth pereopod (distal corneous scales missing); (H) sixth thoracic sternite, ventral view; (I) coxae of fifth pereopods and eighth thoracic sternite, ventral view; (J) telson, dorsal view – inset, terminal margin, posterodorsal view. Notes: Scale bars, (A, C–F) 1 mm; (B, G–J) 0.5 mm.

Figure 18. Pagurixus formosus sp. nov. (A–B) Holotype, male (shield length [SL] 2.9 mm; FMNH 5179): (A) right cheliped, mesial view; (B) right cheliped, lateral view; (C–D) ovigerous female (SL 3.0 mm; FMNH 5179b): (C) right cheliped, mesial view; (D) right cheliped, lateral view. Notes: Scale bars, (A–B) 2 mm; (C–D) 1 mm.

Figure 19. Pagurixus formosus sp. nov. (A, D–F) Holotype, male (shield length [SL] 2.9 mm; FMNH 5179a); (B–C) paratype, ovigerous female (SL 3.0 mm; FMNH 5179b). (A) Right chela and carpus, dorsal view; (B) right chela, dorsal view; (C) carpus of right cheliped, dorsal view; (D) left chela and carpus, dorsal view; (E) left cheliped, mesial view; (F) left cheliped, lateral view. Notes: Scale bars, (A) 2 mm; (B–F) 1 mm.