Pagurus truncatispinosus, Komai & Rahayu, 2014

Komai, Tomoyuki & Rahayu, Dwi Listyo, 2014, New records and new species of the hermit crab genus Pagurus Fabricius, 1775 (Crustacea: Decapoda: Anomura: Paguridae) from the Philippines, Raffles Bulletin of Zoology 62, pp. 620-646 : 636-643

Pagurus truncatispinosus , new species

( Figs. 10–13 )

Material examined. Holotype: male (sl 7.2 mm) ( NMCR 39117 ), PANGLAO 2004, PN1, Balicasag Island , coll. local fisherman, 29 April 2004, tangle nets.

Paratypes: 1 ovigerous female (sl 3.8 mm) ( ZRC 2014.0307 ), PANGLAO 2004, stn T2, 3 Bolod , Panglao Island, 09°32.4'N, 123°47.8'E, 152 m, coarse sand, 31 May 2004 ; 1 male (sl 4.1 mm) ( ZRC 2014.0308 ), stn T27, between Panglao and Pamilacan islands, 09°33.4'N 123°51.0'E, 106–137 m, fine sand and mud with echinoderms, 25 June 2004 ; 3 males (sl 3.0– 4.6 mm), 3 juveniles (sl 1.8–2.3 mm) ( ZRC 2014.0309 ), stn T36, Cervera Shoal , West Pamilacan Island, 09°29.3'N, 123°51.5'E, 95–128 m, sand, echinoderm beds, 4 July 2004 ; 1 ovigerous female (sl 3.5 mm) ( CBM-ZC 12487 ), stn T37, same locality, 09°28.2'N, 123°50.7'E, 134–190 m, 4 July 2004 ; 2 males (sl 3.5, 5.2 mm) ( NMCR 39118 ), stn T39, same locality, 09°30.1'N, 123°50.4'E, 100–138 m, muddy sand, 6 July 2004 ; 1 male (sl 2.8 mm) ( ZRC 2014.0310 ), stn T41, same locality, 09°29.7'N, 123°50.2'E, 110–112 m, 6 July 2004 ; 1 male (sl 7.0 mm) ( ZRC 2014.0311 ), Balicasag Island , May 2004, coll. Nato ; 1 male (sl 4.5 mm) ( ZRC 2014.0312 ), Maribohoc Bay , Panglao Island, 100–300 m, coll. local fishermen, November 2003 to April 2004, tangle nets.

Description. Eleven pairs of biserial gills.

Shield ( Fig. 10A ) slightly wider than long or as long as wide; anterior margin between rostrum and lateral projections gently concave; anterolateral margins sloping, each with shallow excavation posteriorly; posterior margin roundly truncate; dorsal surface very slightly convex transversely, with few tufts of short setae on either side of midline, median part uncalcified; paragastric grooves faint. Rostrum broadly rounded or broadly triangular, slightly falling short of or reaching level of lateral projections. Lateral projections roundly triangular, each with minute submarginal spine. Posterior carapace (not figured) approximately as long as shield; carapace lateral lobe moderately narrow, well calcified; cardiac sulci slightly diverging posteriorly, reaching nearly to posterodorsal margin; sulci cardiobranchiales nearly parallel, not reaching midlength of posterior carapace; posteromedian plate and posterolateral plates moderately well calcified, almost glabrous; branchiostegite membranous, with sparse short to moderately long, plumose setae.

Ocular peduncles (including cornea) ( Fig. 10A ) stout, slightly constricted at proximal 0.3 and increasing in width distally, 0.7–0.8 times as long as shield; not particularly inflated basally; cornea dilated, its width about 0.6 of peduncular length; dorsal surface with two to four tufts of short setae on midline and one additional tuft mesially. Ocular acicles roundly subtriangular, separated basally by width of one acicle, each with minute submarginal spine distally; dorsal surface shallowly concave. Interocular lobe clearly visible, medially concave.

Antennular peduncles ( Fig. 10A ), when fully extended, overreaching distal corneal margins by 0.7–0.8 length of ultimate segment. Ultimate segment about 2.0 times as long as penultimate segment, slightly widened distally in lateral view, with widely spaced, moderately long setae on dorsal surface (tuft of two or three setae at dorsolateral distal angle). Basal segment with distolateral margin not distinctly produced; statocyst lobe weakly inflated, lateral margin fringed with short stiff setae and with minute spine distally; ventromesial distal angle not produced, bluntly pointed.

Antennal peduncles ( Fig. 10A ) overreaching distal corneal margins by 0.2–0.3 length of fifth segment, with supernumerary segmentation. Fifth and fourth segments with some tufts of long setae mesially and laterally. Third segment with small spine at ventromesial distal angle partially obscured by tuft of long setae. Second segment with dorsolateral distal angle moderately produced, reaching midlength of fourth segment, terminating in simple or bifid, acute spine partially obscured by tuft of moderately long setae; dorsomesial distal angle with minute spine; mesial face with sparse short setae. First segment with spinule distally on lateral face; ventrodistal margin with one prominent process lateral to excretory pore. Antennal acicle slightly overreaching distal corneal margin, slightly sinuous, terminating in small spine obscured by distal long setae; dorsomesial margin with several tufts of long setae. Antennal flagellum exceeding five times as long as shield; each article with some very short setae on distal margin.

Mouthparts not dissected. Third maxilliped ( Fig. 10B ) moderately slender; dactylus subequal in length to propodus; carpus unarmed on dorsodistal margin; merus unarmed on dorsodistal and ventral margins; ischium with crista dentata consisting of clearly spaced, relatively large, blunt corneous teeth (middle teeth largest), and with one strong accessory tooth ( Fig. 10C ); basis-ischium fusion incomplete; basis with one or two denticles on mesial margin (not illustrated); exopod nearly reaching midlength of carpus.

Chelipeds distinctly unequal and dissimilar ( Figs. 11, 12). Right cheliped ( Fig. 11A–E) moderately stout, not particularly elongate. Chela elongate subovate in dorsal view, 2.5–2.8 times as long as wide; spines on dorsal surface large, erect, subcylindrical, each with slightly forwardly curved, roundly truncate apex; no hiatus between fingers. Dactylus subequal in length to palm, nearly straight, overlapped by fixed finger distally; dorsal surface with three or four prominent spines in proximal half, unarmed in distal half; dorsomesial margin with row of prominent spines decreasing in size distally and becoming double row proximally; mesial surface with irregular row of small tubercles extending nearly to tip; ventral surface unarmed; all surfaces with scattered tufts of short to long stiff setae, setae on dorsomesial margin particularly long; cutting edge with row of low, rounded calcareous teeth of various sizes, terminating in tiny corneous claw. Palm about 0.8 times as long as carpus; dorsal surface gently convex, armed with prominent spines arranged in 5–7 irregular longitudinal rows and sparse tufts of short setae; distalmost spine of median row, located at proximal to base of dactylus, particularly prominent, bearing scattered short setae, but other spines mostly glabrous or with few short setae at base; proximal transverse groove very deep; dorsomesial margin delimited by row of prominent spines; dorsolateral margin delimited by single or double row of small acute spines on palm and by prominent, subtruncate spines on fixed finger, and with tufts of long setae directed laterally; lateral surface with numerous scattered, small blunt tubercles each bearing tuft of moderately long setae; mesial face with row of subtruncate spines dorsally and several scattered tubercles each bearing tuft of moderately long setae; ventral surface gently convex, with scattered tiny, low tubercles or protuberances each bearing tufts of short setae. Fixed finger nearly straight, somewhat depressed dorsoventrally; dorsal surface and dorsolateral margin with prominent subtruncate spines continued from palm; ventral surface unarmed, with tufts of long stiff setae arranged in some longitudinal rows; cutting edge with row of low calcareous teeth in proximal 0.7, crenulate in distal 0.3, terminating in small calcareous claw. Carpus moderately widened distally, subequal in length to merus; dorsal surface with 2 irregular longitudinal rows of small to moderately large spines in mesial half and with scattered, moderately small blunt tubercles each bearing tuft of long setae, extending onto lateral surface; dorsomesial margin delimited by double row of moderately small to large spines; dorsodistal margin with row of tiny spines; dorsolateral margin not delimited; lateral surface with numerous scattered, setae-bearing tubercles, becoming smaller and more closely spaced ventrally; mesial surface faintly concave, with scattered, numerous small tubercles and tufts of long setae obscuring armature; ventral surface flat, covered with tiny tubercles, provided with large, deep, pinhole-like foramen medially ( Fig. 11E). Merus dorsally with irregular rows of short transverse ridges or low protuberances (margins of these structures multidenticulate) becoming weak proximally, each ridge bearing tuft or row of moderately short setae; dorsodistal margin minutely denticulate, with four prominent spines; lateral surface with short vertical ridges and small ventral spines or tubercles, ventrolateral distal margin with row of prominent spines; mesial surface with sparse, short vertical ridges or minute granules and several small ventral spines or tubercles (these armature bearing tufts of short setae), ventromesial distal margin with row of small tubercles; ventral surface armed with numerous small spines or tubercles and with numerous tufts of moderately long plumose setae partially obscuring armature. Ischium with row of tiny, low tubercles on ventromesial margin; lateral surface nearly smooth, ventrolateral distal angle with one or two spinules or spiniform tubercles. Coxa unarmed.

Left cheliped ( Fig. 12A–D) moderately slender. Chela 2.5–2.8 times as long as wide (greatest width at base of dactylus), with numerous tufts of short to long setae on lateral, mesial and ventral surfaces; no hiatus between fingers. Dactylus approximately twice longer than palm; dorsal surface with partially double row of moderately small, subcylindrical spines with blunt apices; mesial surface with irregular longitudinal rows of low protuberances or small spines obscured by tufts of long setae; ventral surface unarmed; cutting edge with row of minute corneous teeth, terminating in small corneous claw. Palm about half length of carpus; dorsal surface slightly convex transversely, armed with very large spines arranged in four irregular longitudinal rows, extending onto fixed finger into single row, and decreasing in size distally; each spine slightly curved forward, with slightly inflated, rounded or subtruncate distal part; dorsomesial margin with single row of smaller, but similarly shaped spines; dorsolateral margin weakly delimited with row of small to moderately large spines extending nearly to tip of fixed finger and decreasing in size distally; lateral and mesial surfaces with few small spines dorsally and scattered small, low, setae-bearing protuberances ventrally; ventral surface with scattered, very low, tiny protuberances and tufts of moderately short setae; cutting edge of fixed finger with row of tiny, obsolescent calcareous teeth interspersed by two or three fused, minute corneous teeth, terminating in moderately small corneous claw. Carpus subequal in length to merus, with tufts of short to long setae each arising from armature on every surface; dorsal midline bluntly carinate, with partially double row of small acute or subacute spines increasing in size distally; lateral and mesial surfaces with numerous scattered, small, low protuberances; ventral surface nearly flat, with numerous tiny tubercles, devoid of even trace of median foramen. Merus with short transverse ridges on dorsal surface, dorsodistal margin with 1 prominent spine; lateral surface with scattered, very short vertical ridges, becoming protuberance-like ventrally, and tufts of short setae, ventrolateral margin with row of moderately large spines decreasing in size proximally; mesial surface with sparse, very short vertical ridges and some small ventral tubercles, and tufts of short setae, ventromesial distal margin with row of tiny spines or tubercles; ventral surface faintly concave medially, with scattered tiny tubercles and tufts of moderately short setae. Ischium with row of minute tubercles on ventromesial margin; ventrolateral margin with row of short, multidenticulate ridges.

Ambulatory legs ( Fig. 13A, E ) moderately long and stout in general, right second pereopod overreaching tip of extended right cheliped by half length of dactylus. Dactyli 1.3–1.5 times as long as propodi, 10–12 times longer than broad, in dorsal view slightly twisted, in lateral view gently curving ventrally; dorsal margins each with row of numerous, short to moderately long (decreasing in length proximally), bristle-like setae, but without conspicuous spines or spinules (proximal parts apparently minutely denticulate because of pockets of bristle-like setae); lateral faces each with faint median sulcus and single row of moderately short to long stiff setae along midline; mesial faces ( Fig. 13B, F ) each with faint to shallow median sulcus flanked dorsally by row of widely spaced, individual or sets of two or three short, bristle-like setae, and ventrally by row of numerous bristle-like setae increasing in length distally; ventral margins each with row of about 30–50 minute, slender corneous spinules becoming widely spaced proximally, distal 10–15 spinules closely spaced, overlapping each other ( Fig. 13C ). Propodi ( Fig. 13D, G ) somewhat narrowing distally; dorsal surfaces each with single or partially double row of tiny spines (spines weaker in third than in second) and short setae, dorsodistal margin with minute granule or spinule (second) or unarmed (third); lateral and mesial surfaces each with sparse minute pits often bearing individual or tufts of short setae, mesial faces of second pereopods bearing minute spinules dorsally; ventral surfaces each with sparse, very short setae (second) or almost glabrous (third), without any armature. Carpi ( Fig. 13D, G ) each with row of small spines on dorsal margin, decreasing in size proximally, and row of sparse short setae (spines much weaker in third than in second); lateral faces convex, with some scattered short setae. Dorsal surfaces of meri with tiny, low protuberances and tufts of short to moderately long setae (second) or only with tufts of similar setae (third); lateral and mesial faces almost glabrous except for few tufts of short setae; ventrolateral distal margins each with 1 tiny spine (second) or unarmed (third), ventral surfaces each with two or three irregular rows of tiny spines or tubercles (on second, armature more numerous in right than in left), or unarmed (third), and with tufts of short to long setae. Ischia unarmed, with moderately short to long setae on dorsal and ventral margins. Female with paired gonopores on coxae of third pereopods.

Fourth pereopods ( Fig. 10D ) semichelate, with stiff long setae on dorsal margins of dactyli to meri and ventral margin of meri. Dactyli gently curved, terminating in prominent corneous claw, each with row of minute, closely spaced corneous teeth on ventral margin; no preungual process. Propodal rasp consisting of four rows of corneous scales.

Fifth pereopods chelate. Coxae of male ( Fig. 10F ) each with gonopore partially masked by tuft of setae.

Thoracic sternite 3 with anterior margin nearly straight, with paired denticles medially; ventral surface with prominent tuft of setae medially. Anterior lobe of thoracic sternite 6 ( Fig. 10E ) subtriangular, approximately as long as wide, distinctly skewed to left, terminally with two small spines; ventral surface with subterminal tuft of long setae. Thoracic sternite 8 ( Fig. 10F ) divided in two similar lobes by shallow median groove; each anterolateral angle slightly produced, with prominent tuft of short setae.

Pleon dextrally twisted. Male with three (third to fifth) unpaired, very unequally biramous left pleopods. Female with subequally or slightly unequally biramous, second to fourth pleopods; fifth pleopod greatly unequally biramous with strongly reduced endopod.

Telson ( Fig. 10G ) with distinct lateral indentations; posterior lobes subrectangular, unequal, with median cleft very shallow, U-shaped; each terminal margin with row of corneous-tipped spines extending onto lateral margin (9–13 on left, 5–9 in right), these spines strongest around lateral angles.

Coloration. In preservative. Entirely light grayish brown.

Distribution. Known only from the Bohol Sea, the Philippines, at depths of 95– 300 m.

Etymology. From the combination of the Latin, truncatis (= truncate) and spinosus (spinose), in reference to the terminally truncate or rounded spines on the palms of the chelipeds.

Remarks. Pagurus truncatispinosus , new species, shares the possession of a pinhole-like ventral foramen on the right cheliped carpus, representing an uncommon feature in Paguridae , with P. cavicarpus , P. conformis , and P. carpoforaminatus , though McLaughlin & Forest (1999) and the present study report that the carpal foramen is not always present in P. cavicarpus and P. conformis , respectively. Other diagnostic characters shared with the four species include: rostrum broadly rounded; ocular peduncle stout with dilated cornea; and propodi and carpi of second pereopods with row of spines on dorsal margins; male with four unpaired left pleopods ( Alcock, 1905b; McLaughlin & Forest, 1999; Komai, 2004; this study). A shallow excavation or notch on the lateral margin of the shield and the triangular anterior lobe of the thoracic sternite 6 are also seen in the new species, P. cavicarpus and P. conformis ; these characters are not known for P. carpoforaminatus because of the lack of a modern description. The characteristic shape of dorsal spines on the palms of both chelipeds immediately distinguishes the present new species from the other three relatives. In P. truncatispinosus , new species, the dorsal spines on the palms of chelipeds have slightly inflated and distally subtruncate or rounded apices, though those spines are acute or subacute and much smaller in the other species. In particular, in P. conformis , the dorsal spines are so small that they are partially obscured by surrounding setae. Furthermore, the proximal transverse groove of the right cheliped palm is unusually deep in P. truncatispinosus , new species; the carpal foramen on the right pereopod is better developed in the new species than in the other three species, though examination of more specimens might reveal that the development of the foramen is variable also in the new species.

Pagurus spinulentus and P. spinossior also resemble P. truncatispinosus , new species, in most of the characters mentioned above, though distinct pinhole-like foramen is absent in the former two species. We suppose that those six species ( P. carpoforaminatus , P. cavicarpus , P. conformis , P. spinossior , P. spinulentus , and P. truncatispinosus , new species) might constitute a monophyletic group. Pagurus spinulentus and P. spinossior are immediately distinguished from the new species in having the strongly produced dorsolateral distal angle of the second segment of the antennal peduncle (reaching the midlength of the fourth peduncular segment versus reaching nearly to the distal margin of the fourth peduncular segment), much more numerous, acuminate spines on both chelae and a shallow, transverse proximal groove on the right cheliped palm. The unarmed dorsal margins of dactyli of the second pereopods (versus armed with row of tiny spines), and the proportionally narrower anterior lobe of the thoracic sternite 6 also distinguish P. truncatispinosus , new species, from P. spinulentus .

Figures

Fig. 10. Pagurus truncatispinosus, new species, PANGLAO 2004, PN1, holotype, male (sl 7.2 mm), NMCR 39117. A, shield and cephalic appendages, dorsal view; B, left third maxilliped, lateral view; C, same, ischium, ventral view (setae omitted); D, distal three segments of left fourth pereopod, lateral view (setae omitted); E, thoracic sternite 6, ventral view; F, coxae of fifth pereopods and thoracic sternite 8, ventral view; G, telson, dorsal view. Scale bars = 2 mm for A, B, F; 1 mm for C–E, G.

Fig. 13. Pagurus truncatispinosus, new species, PANGLAO 2004, PN1, holotype, male (sl 7.2 mm), NMCR 39117. A, right second pereopod, lateral view (bristle-like setae on proximal half of dorsal margin of dactylus broken off); B, same, dactylus, mesial view; C, same, detail of distal part of dactylus, mesial view; D, same, propodus and carpus, mesial view (setae omitted); E, left third pereopod, lateral view; F, same, dactylus, mesial view (dorsal setae omitted); G, same, propodus and carpus, mesial view (setae omitted). Scale bars = 5 mm (A, D, E, G); 2 mm (B, F); 0.5 mm (C).