Paguristes jalur Morgan, 1992

Osawa, M. & Takeda, M., 2004, Hermit crabs (Crustacea: Decapoda: Anomura: Paguroidea) from submarine caves in the Ryukyu Islands, south-western Japan, Journal of Natural History 38, pp. 1097-1132 : 1099-1109

Paguristes jalur Morgan, 1992

(figures 1–4)

Paguristes jalur Morgan, 1992: 167 , figures 1, 2.

Material examined. NSMT-Cr 14378; one male (SL 6.7 mm), one female (SL 3.4 mm), one ovigerous female (SL 5.8 mm); Shimoji islet, Miyako Group; ‘ Coral Hole’ ; 24°48.0∞N, 125°09.0∞E; 24–35 m; 31 July 1999 . NSMT-Cr 14379; two males (SL 3.6, 4.6 mm), two females (SL 3.9, 5.1 mm), two ovigerous females (SL 4.1, 5.2 mm); Maeda-misaki (Cape of Maeda), Onna , Okinawa Island ; horizontal holes or crevices on fore-reef slope; 2 m; 7 July 2000; collected by M. Osawa.

H  : WAM 459-89 ; male (SL 4.8 mm); Horburgh Island (St. 4), Cocos (Keeling) Islands; to 37 m; 9 February 1989; collected by G. J. Morgan. P    : WAM 406-92 ; two females (SL 2.6, 3.3 mm) ; same data as holotype .

Redescription. Thirteen pairs of biserial phyllobranchiate gills, two pairs of welldeveloped arthrobranchs present on each third maxilliped and first to fourth pereopod, single well-developed pleurobranch on each fifth to seventh thoracic somite (above arthrobranchs of second to fourth pereopods).

Shield (figure 1A) approximately 0.6 total carapace length; maximum shield width 0.8 length; dorsal surface with very short rugae, rugae of median lateral areas longer and bearing moderately long plumose setae and small denticles anteriorly; gastric region slightly elevated, with short, shallow median sulcus; anterolateral margins sloping; anterior margin between rostrum and lateral projections concave; posterior margin roundly truncate. Rostrum moderately narrowly triangular, terminating in spinule, somewhat curved ventrally; distinctly over-reaching lateral projections and reaching to proximal 0.3 of ocular acicles; dorsal surface indistinctly or weakly carinate; lateral margin unarmed. Lateral projections broadly triangular, each with small submarginal spine. Branchiostegites (figure 1C) calcified anteriorly and dorsally, each with row of small spines on anterodorsal margin.

Ocular peduncles (figure 1A) long, slender (8.0–8.2 times longer than width of cornea), 0.7–0.8 times as long as shield, cylindrical, inflated basally; corneas not dilated, with basal width practically equal to minimum width of peduncles; dorsomesial basal surfaces of peduncles each with longitudinal row of tufts of moderately long setae bearing minute lateral setules. Ocular acicles subtriangular, terminating in small acute spine, separated by approximately half of basal width of one acicle; mesial margin slightly convex, with few short setae.

Antennular peduncles (figure 1A, B) when fully extended, slightly shorter than ocular peduncles, only reaching to or just over-reaching base of cornea. Ultimate segment 0.7–0.8 times longer than penultimate segment, somewhat deeper distally, naked or with few very short setae distally. Penultimate segment unarmed but with scattered tufts of short or moderately long setae. Basal segment deeply notched on ventrodistal margin, with moderately long setae on ventral angles and statocyst lobe; ventromesial distal angle more strongly produced than ventrolateral angle, terminating in small spine; ventrolateral angle unarmed, rounded; dorsolateral margin with small spine and moderately long setae Upper flagellum elongate, 2.1 times longer than ultimate peduncular segment, lower flagellum reaching nearly to half length of upper flagellum.

Antennal peduncles (figure 1A, C) when fully extended, reaching 0.7–0.8 length of ocular peduncles; with supernumerary segmentation. Fifth segment unarmed but with few short setae bearing minute lateral setules. Fourth segment unarmed or with small spine on dorsolateral distal margin, nearly naked. Third segment with ventromesial distal angle strongly produced, terminating in small spine, bearing moderately long plumose setae marginally. Second segment with dorsolateral distal angle strongly produced, terminating in bifid spine; dorsomesial distal angle with small spine; dorsomesial margin ridged; dorsolateral margin subacute; mesial and lateral faces with short or moderately long plumose setae. First segment unarmed on entire margins, ventromesial margin strongly produced. Antennal acicles relatively slender, reaching 0.7–0.9 length of fifth segment of peduncle and 0.6–0.7 length of ocular peduncles, terminating in strong spine, with tufts of long setae marginally; mesial margin with two to five spines in proximal half; lateral margin with two or three spines in distal half. Antennal flagella (figure 1D) in complete condition 1.5–1.8 times longer than total carapace measured along dorsal midline (2.5–3.0 times longer than shield), distinctly exceeding tips of chelipeds, composed of approximately 80 articles; each article usually with several very short setae on distal margin.

Endopod of maxillule (figure 1E) moderately slender, with single short seta on mesial margin; internal lobe strongly produced, with 11 bristles on rounded distal margin; external lobe very well developed, elongate, strongly recurved, distolateral margin with two short setae. Third maxilliped (figure 1F, G) with propodus and dactylus entirely unarmed; carpus unarmed or with very small spine at dorsodistal angle, ventrodistal angle unarmed or with small spine; merus with three to five spines on ventral margin, dorsodistal margin unarmed or with very small spine; ischium with well-developed crista dentata composed of small, numerous, subequal corneous teeth becoming closer proximally, ventrodistal angle with small or moderately strong spine, dorsodistal angle strongly produced but unarmed; basis apparently separated from ischium, with three small spines on dorsomesial margin; coxa bearing three small spines at ventrodistal angle.

Chelipeds (figure 2A–C) moderately short, subequal or slightly unequal with right larger than left, inequality most distinct in largest male examined (NSMT-Cr 14378, SL 6.7 mm), generally similar in form and armament. Chela subovate in dorsal view, 1.7–2.2 times longer than broad, with moderately narrow hiatus between dactylus and fixed finger; fingers each terminating in small corneous claw. Dactylus 1.2–1.4 times longer than palm, slightly curved ventrally near base, usually overlapped distally by fixed finger when closed; dorsomesial margin with row of moderately strong spines, usually arranged in double row proximally and decreasing in size distally; dorsal surface with longitudinal row of small tubercles along cutting edge, distinct sulcus present between tubercles and dorsomesial row of spines; mesial surface slightly concave or flattish, with row of small spinulose tubercles in midline; ventromesial margin delimited by small spinulose tubercles; ventral surface with row of very small tubercles in midline; cutting edge with row of small, blunt calcareous teeth in proximal 0.6–0.8 (proximal tooth noticeably or moderately enlarged) and small, ovate corneous teeth in distal 0.2–0.4. Palm 0.7–0.9 times longer than carpus, swollen ventrally, with fixed finger distinctly broader than dactylus and weakly curved ventrally, terminating in small corneous claw; dorsomesial margin with row of four or five spines, distal four spines strong, proximalmost spine small or absent; dorsal surface with longitudinal rows of small spines and spinulose tubercles, larger spines or tubercles present on weakly or moderately well-developed, median ridge extending on to fixed finger along cutting edge, surface between median ridge and dorsomesial margin slightly or moderately concave, shallow or moderately deep, broad sulcus present along dorsomidline of fixed finger and usually bearing several small spinulose tubercles distally (tubercles sometimes arranged in single or double rows or indistinct); dorsolateral margin delimited by row of moderately strong spines decreasing in size proximally and distally on fixed finger; mesial face with short row of spinulose tubercles ventral to dorsomesial margin distally and small spinulose tubercles along distal margin; lateral surface slightly convex, with irregular row of small or moderately strong spines or spinulose tubercles ventral to dorsolateral margin and scattered small spinulose tubercles; ventromesial margin with short row of small spinulose tubercles or protuberances distally, distal angle (proximal to base of fixed finger) noticeably inflated; ventrolateral margin weakly delimited, with small spinulose tubercles; ventral surface with ridge of spinulose tubercles or protuberances in midline, extending on to fixed finger and decreasing in size distally; cutting edge of fixed finger with row of blunt calcareous teeth and few small, rounded corneous teeth near tip. Carpus 0.5–0.8 times as long as merus; dorsomesial margin delimited by row of four to six strong spines becoming larger distally, occasionally accompanied by few smaller spines; dorsal surface with longitudinal elevated row of small spines or spinulose tubercles in midline and several irregular rows of smaller tubercles; dorsodistal margin moderately produced, with row of small spines lateral to articular knob; dorsolateral margin delimited by row of small spines becoming larger distally; mesial surface with few, short transverse scales dorsodistally; lateral surface with irregular row of small spinulose tubercles and protuberances along dorsolateral and distal margins; ventral surface with few low, spinulose protuberances laterally, ventrodistal margin produced, with small spine or tubercle. Merus deep, compressed laterally, acutely triangular in dorsal view; dorsal surface distinctly subacute in proximal half, with longitudinal ridge of transverse scales anteriorly bearing minute corneous spinules and decreasing in size proximally, distal scale extending to mesial and lateral surfaces; dorsodistal margin with row of small or minute corneous spines, median spine larger; mesial surface nearly smooth, with shallow vertical sulcus near distal margin; lateral surface with scattered, transverse short scales ventrally; ventromesial margin with row of irregular-sized spines and spinulose tubercles, median spines much larger; ventrolateral margin sinuous, with small spinulose tubercles and protuberances medially and sharply pointed spine near distal end; ventral surface unarmed, smooth, slightly concave. Ischium with dorsodistal angle rounded, unarmed; ventral surface with tiny tubercles on longitudinal ridge mesially; distomesial and distolateral margins with few very small tubercles or spinules ventrally. Coxa with few spinules on distomesial and distolateral margins. Most spines, tubercles and protuberances of all segments each with small corneous apex and accompanied by tuft of long or moderately long plumose setae, setae bearing minute lateral setules and most numerous on dorsal surface of chela and carpus.

Second pereopods (figure 3A–C) moderately long and stout, generally similar from right to left, over-reaching tip of chelipeds by proximal 0.3–0.5 of dactyli; right dactylus slightly longer than left. Dactyli long, 1.3–1.7 times longer than propodi, slender, weakly curved ventrally in lateral view, nearly straight or weakly curved mesially in dorsal view, terminating in moderately curved corneous claw; dorsal margins each with row of calcareous spinules in proximal 0.8–0.9; lateral surfaces each with shallow longitudinal sulcus proximally in midline; mesial surfaces unarmed but each with strong longitudinal ridge along midline, concave dorsal to ridge; ventral margins each with row of 12–20 small, short, corneous spines in distal 0.8–0.9, size of spines decreasing proximally. Propodi 1.1–1.3 times longer than carpi, 2.5–3.0 times as long as high; dorsal surfaces each with row of subequal, strong spines mesially, distomedian angles each with one or two moderately large or small spines; lateral surfaces with weakly marked, irregular-sized, transverse or oblique rugae, shallow longitudinal sulcus present along dorsal margin; laterodistal margins with few small spines near both dorsal and ventral angles or only ventral angle; mesial surfaces unarmed but with shallow, short, oblique rugae, longitudinal sulcus present along dorsal margin (more distinctly developed in distal part); mesiodistal margins with few or several small spines; ventral faces protuberant, with single or double row of small, short, corneous spines in distal half. Carpi moderately long, 0.6–0.7 times longer than meri; dorsal surfaces each with row of four to six spines mesially, spines usually becoming larger distally; dorsodistal lateral angle with strong spine; lateral surfaces strongly convex, slightly rugose dorsally, each with longitudinal ridge on submedian line of dorsal side, distal angle of ridge unarmed or with small spine; mesial surfaces with faintly marked, short, transverse rugae; ventral surfaces apparently smooth. Meri strongly compressed laterally; dorsal surfaces slightly crenulated or with spinules; lateral surfaces with short, oblique rugae along dorsal and ventral margins, short distomedian sulcus present; ventrolateral margin with subdistal small spine; mesial surfaces with short, oblique rugae on dorsal half, short distomedian sulcus present; ventromesial distal angle slightly or moderately produced but unarmed; ventral surfaces each with longitudinal row of irregular-sized spines and protuberances medially. Ischia unarmed or slightly crenulated on dorsal faces; lateral, mesial and ventral surfaces almost smooth; ventral surfaces unarmed. Coxae unarmed. Most strong spines on propodi, carpi and meri each with small corneous apex. All segments with numerous long and short setae, more densely fringed on dorsal and ventral surfaces and mesial longitudinal ridges of propodi and dactyli; most setae plumose, bearing minute lateral setules.

Third pereopods (figure 3D, E) generally similar from right to left, structure on lateral and mesial surfaces and setation generally similar to those of second, right dactylus and propodus slightly longer than those of left. Dactyli 1.3–1.5 times longer than propodi; dorsal margins each with row of calcareous spinules in proximal 0.7–0.8, size of spinules smaller than those of second; ventral margins each with row of 11–20 small, short, corneous spines. Propodi 1.1–1.2 times longer than carpi, 2.4–3.0 times as long as broad, tapering in height distally; dorsal surfaces unarmed except for one or two small spines or spinules at each distomedian angle; laterodistal margins unarmed or with few spinules near ventral angle; mesial surface with weakly developed, longitudinal sulcus along dorsal margin; mesiodistal margins with few or several spinules; ventral surfaces protuberant, unarmed or with single row of small, short, corneous spines in distal half. Carpi approximately 0.8–0.9 times longer than meri; dorsal surfaces usually slightly crenulated but unarmed except for strong spine at lateral distal angle, sometimes with one to three small proximal spines mesially; longitudinal ridge on lateral surface unarmed at distal angle. Meri less compressed laterally and more inflated ventrally than those of second; dorsal surfaces slightly crenulated, sometimes with distal spinule; ventrolateral margins each with subdistal small spine; ventromesial distal angles produced but unarmed; ventral faces each with short, longitudinal row of irregular-sized spines and protuberances medially. Ischia unarmed but weakly crenulated on dorsal surfaces, ventral surfaces unarmed. Coxae unarmed, with paired gonopores in females and largest male examined (NSMT-Cr 14378, SL 6.7 mm).

Fourth pereopods (figure 1H) equal in size, semi-chelate, setose on dorsal and ventral surfaces. Dactylus slightly curved, terminating in small corneous claw; dorsal surface unarmed; ventral surface with row of four to six small corneous teeth laterally and slender, chitinous, tube-like preungual process arising from proximal base of terminal claw. Propodus moderately stout, with almost straight ventral margin; dorsal margin weakly convex, unarmed but slightly crenulated; propodal rasp composed of five or six irregular rows of ovate corneous scales, becoming fewer proximally, occupying distal 0.7 length of ventral margin. Carpus with strong spine on dorsodistal margin.

Fifth pereopods equal in size; chelate; slender, setose, setae most numerous on palm. Coxae of males usually with paired gonopores, but with unpaired right gonopore in largest examined (NSMT-Cr 12378, SL 6.7 mm).

Abdomen well developed, coiled. Second and third abdominal tergites moderately or weakly calcified and with row (male) or dense fringe (female) of soft setae on lateral longitudinal ridge on left side; fourth abdominal tergite poorly developed, with no tuft of setae. Brood pouch in female (figure 4I, J) very well developed, semicircular or roundly rectangular, arising from posterior base of fourth pleopod, formed by large fold of tissue, completely covering second to fourth pleopods (eggs mainly attached to third and fourth pleopods); margins indented, fringed with short or moderately long delicate setae; outer face with scattered short setae.

First and second pleopods (figure 4A–H) in male paired, equal in size, modified as gonopods. First pleopod (figure 4A–D) with single or double row of moderately long setae on mesial surface and few short setae on ventral surface of basal segment. Inferior lamella moderately twisted, with obtuse longitudinal ridge on ventral surface, continuous with proximolateral margin; distal margin broadly rounded, with row of moderately strong, closely set, hooked corneous spines; mesial margin with double row of moderately long setae; lateral margin strongly sinuous. External lobe well developed, rounded, distinctly over-reaching distal margin of inferior lamella. Internal lobe moderately large, rounded, separated from external lobe by U-shaped notch; mesial margin with long setae and small denticles.

Second pleopod (figure 4E–G) with basal segment slightly flattened and bearing few setae proximally. Endopod somewhat flattened, twisted; margins bluntly edged, with row of moderately long setae on lateral margin; mesial surface with row of moderately long setae distally. Appendix masculina expanded, moderately broad, twisted, not noticeably elongate distally; articulation suture discernible only on interior (mesial) face; distal margin rounded; exterior (lateral) face concave, with numerous long setae; ventral margin weakly produced somewhat distal to midlength, with tuft of moderately long setae; interior (mesial) face sulcate, with moderately long setae dorsally. Third to fifth pleopods in male unpaired, similar in size, unequally biramous; exopods well developed but endopods very small; both rami fringed with plumose setae marginally.

Pleopods of female with first (figure 4H) paired, equal in size; articulation between basal and distal segments obsolete; basal segment not curved, slightly broadened basally, with long plumose setae marginally; distal segment elongated ovate, slightly longer and narrower than basal segment, with long plumose setae marginally. Second to fifth pleopods unpaired; second to fourth pleopods with both rami well developed, exopods much longer than endopods, multi-articulated, endopods biarticulated, bearing long plumose setae marginally; fifth pleopod much shorter than preceding pleopods, with exopod moderately well developed, not articulated, endopod greatly reduced.

Uropods strongly asymmetrical; protopods each with rasp of scales on posteroventral surface; endopods much smaller than exopods, rounded, each with rasp of scales occupying distal half of posterior surface; exopods paddle-shaped, each with rasp of scales occupying dorsal half of distal two-thirds of posterior surface.

Telson (figure 4I) with clearly delimited, deep transverse identations on lateral margins; anterior lobes unarmed and with tufts of long setae on convex lateral margins; posterior lobes moderately or distinctly asymmetrical, left lobe larger than right; each lobe subovate or subtriangular with rounded apex, separated by deep or moderately deep median cleft; terminal and lateral margins unarmed but with long and short setae; dorsal surface with scattered tufts of short and moderately long setae.

Colour. The coloration and stripe pattern of the specimens examined generally agreed well with that of Morgan (1992). When the specimens were first examined, longitudinal red stripes could be seen in the chelipeds and ambulatory legs; but these have now mostly faded in the preserved condition.

Habitat. This species is found from not only submarine caves but also small crevices or horizontal holes on fore-reef slopes in the Ryukyu Islands. The bottoms of the crevices and holes are thickly covered with fine sand or sediments.

Distribution. This species was previously known only from the Cocos (Keeling) Islands and Christmas Island in the eastern Indian Ocean, and Guam in the western Pacific (Morgan, 1992; McLaughlin, 2002b). The present record from the Ryukyu Islands extends its geographical distribution northwards. Paguristes jalur occurs at depths of 2– 37 m.

Remarks. The specimens examined from the Ryukyu Islands agree well morphologically with the holotype and paratypes of P. jalur . Although Morgan (1992) described the propodi of the second and third pereopods as nearly smooth on the lateral and mesial surfaces, the present examination of the type material (holotype and two of five paratypes) and other available specimens reveals in fact that these surfaces have numerous, weakly marked, transverse or oblique rugae. As illustrated by Morgan (1992: 167, figure 2A), the chelae have a rather distinct longitudinal sulcus on the dorsal surface of each dactylus and fixed finger.

Paguristes jalur resembles P. acanthomerus Ortmann, 1892 , P. alegrias Morgan, 1987a and P. runyanae Haig and Ball, 1988 in having antennular peduncles shorter than the ocular peduncles, antennal flagella longer than the carapace (shield and posterior carapace), and right cheliped larger or stouter than the left, at least in males. Paguristes mundus Alcock, 1905 also seems to possess the same characters, although a minor discrepancy is seen between the original figure and description of the chelipeds. In the original figure (Alcock, 1905: plate 3, figure 5) of the species, the right cheliped is shown as larger than the left, but the description cites the chelipeds as subequal. Among these species, the unarmed terminal margin of the telson links P. jalu r to P. acanthomerus and P. runyanae ; although the morphology of the telson has not been described for P. mundus . The unarmed terminal margins of the telson provide evidence that P. jalur , P. acanthomerus and P. runyanae should be placed in group B of Paguristes Dana, 1851 (see McLaughlin and Provenzano, 1974). Paguristes jalur is closest to P. runyanae in shape and ornamentation of the chelipeds, pereopods, and male first and second pleopods, but is distinguished from the latter species by the shorter ocular peduncles (only just exceeding the antennular peduncles in P. jalur , whereas 1.3–1.5 times longer than the antennular peduncles in P. runyanae ); the dactyli of the second and third pereopods each lacking a median, longitudinal row of corneous spinules on the mesial surface; the carpi of the third pereopods having no or much smaller spines mesially on the dorsal surface; and the heavier setation of the chelipeds and pereopods. Both species also have distinctively striped legs, but the colour in life is clearly different. Paguristes jalur has a cream or white shield and ocular, antennular and antennal peduncles, and cream or pale orange legs with maroon or dark red stripes (broad irregular annulus subdistally, often smaller patches proximally on the meri of the second and third pereopods); whereas P. runyanae possesses a purple shield with orange stripes, purple ocular, antennular and antennal peduncles, and purple and orange or white striped legs (longitudinal stripes on the meri of the second and third pereopods) (see Haig and Ball, 1988; Morgan, 1992).

The inequality of the chelipeds, the right cheliped larger, is most distinct in the largest male specimen examined (NSMT-Cr 14378, SL 6.7 mm). In addition to P. jalur and its allied species mentioned above, the slightly larger right cheliped is also known in males at least of P. hians Henderson, 1888 (McLaughlin and Clark, 1997).

The largest specimen examined (NSMT-Cr 14378, SL 6.7 mm) has an unpaired male gonopore on the coxa of the right fifth pereopod and paired female gonopores on the coxae of the third pereopods. However, this specimen is regarded as a fully functional male, since the first and second pleopods, modified as gonopods, are well developed, and each pair is equal-sized, and the third and fourth pleopods are unequally biramous with very small endopods. The other smaller male specimens including the type material have paired gonopores on the coxae of the fifth perepods and lack female gonopores. The presence of a gonopore only on the coxa of the right fifth pereopod in males is also reported as a specific character in P. monoporus Morgan, 1987b . In addition to this character, P. monoporus is a rather bizarre species of Paguristes in having a greatly reduced left first pleopod and unpaired right second pleopod in males, and an unpaired gonopore on the coxa of the left third pereopod in females (Morgan, 1987b).