Trichopagurus tenuidactylus, Komai, Tomoyuki, 2013

Komai, Tomoyuki, 2013, Additional records of the pagurid hermit crab genus Trichopagurus de Saint Laurent, 1968 (Crustacea: Decapoda: Anomura), with description of a new species from the Philippines, Zootaxa 3670 (2), pp. 274-282 : 275-279

Trichopagurus tenuidactylus n. sp.

( Figs. 1 –3)

Material examined. Holotype: PANGLAO 2004, stn L41, off Panglao Island, Bohol, Philippines, 09°31.3'N, 123°41.2'E, 90–100 m, 1 July 2004, ovigerous female (sl 1.4 mm), NMCR 39078.

Description. Eleven pairs of biserial gills.

Shield ( Fig. 1 A) 1.1 times longer than wide; anterior margin between rostrum and lateral projections slightly concave; anterolateral margins sloping; posterior margin roundly truncate; dorsal surface weakly convex, with some tufts of short setae laterally; no paragastric groove delineated. Rostrum triangular, reaching midlength of ocular acicles, tip rounded. Lateral projections obsolete, with small submarginal spine.

Ocular peduncles (including cornea) ( Fig. 1 A) stout, about 0.7 times shield length; slightly narrowing basally; cornea not dilated, corneal width about half of peduncular length; dorsal surface with tuft of short stiff setae near base of cornea mesially and 1 tuft of longer setae medially. Ocular acicles subtriangular, moderately widely separated, each with small submarginal spine terminally; dorsal surface flat.

Antennular peduncles ( Fig. 1 A) slender, when fully extended, overreaching distal corneal margins by half length of ultimate segment. Ultimate segment approximately twice length of penultimate segment, slightly widened distally, with tuft of long setae at dorsodistal lateral angle. Penultimate segment short, without setae. Basal segment with distolateral margin distinctly produced as short process, statocyst lobe weakly inflated, unarmed laterally.

Antennal peduncles ( Fig. 1 A) slightly overreaching distal corneal margins. Fifth and fourth segments with few stiff setae. Third segment with spinule at ventromesial distal margin (not visible in dorsal view). Second segment with dorsolateral distal angle produced, slightly falling short of midlength of fourth segment, terminating in simple, acute spine; dorsomesial distal angle with small spine; mesial and lateral faces glabrous. First segment with minute spine on lateral face; ventromesial distal margin somewhat produced anteriorly, spineless. Antennal acicle overreaching base of cornea but not reaching distal corneal margin, terminating in small spine; dorsomesial margin with sparse moderately long setae. Antennal flagellum more than 5.0 length of shield, distinctly overreaching extended right cheliped; each article with 3–5 very short to moderately long setae on distal margin.

Mouthparts not dissected. Third maxilliped moderately slender; carpus unarmed on dorsodistal margin; merus with strong dorsodistal spine and small ventromesial spine; ischium with well-developed crista dentata composed of very small corneous teeth and 1 accessory tooth; basis-ischium fusion incomplete; basis unarmed on ventromesial margin; exopod reaching midlength of carpus.

Chelipeds ( Figs. 1 B, C; 2A–D) strongly unequal and dissimilar. Right cheliped ( Figs. 1 B; 2A, B) moderately large. Chela suboval in dorsal view, about 2.5 times as long as wide (greatest width at midlength of palm). Dactylus about 0.8 length of palm, slightly curved ventrally; dorsal surface with sparse microscopic granules, dorsomesial margin not delimited, all surfaces with sparse short setae; cutting edge with 2 large, blunt calcareous teeth in proximal 0.7 and row of minute corneous teeth in distal 0.3, terminating in small corneous claw. Palm subequal in length to carpus, with sparse short setae on surfaces; dorsomesial margin not delimited, dorsolateral margin delimited by irregularly interrupted carina extending onto midlength of fixed finger; dorsal surface gently convex, with few, minute tubercles proximally; lateral and ventromesial faces almost smooth; ventral surface convex, smooth, with scattered moderately long setae. Fixed finger with scattered short setae on dorsal surface; cutting edge with 2 obtuse teeth in proximal half and row of minute corneous teeth in distal 0.4, terminating in small corneous claw. Carpus somewhat flattened dorsoventrally, slightly widened distally, slightly shorter than merus; dorsomesial margin not delimited, with 3 moderately large spines and 1 low proximal protuberance, with short to long stiff setae; dorsolateral margin not delimited; dorsal surface slightly convex transversely, with few short, sometimes spiniform setae; lateral surface with some low, short ridges sometimes bearing short stiff setae, ventrolateral distal angle with 1 small spine; mesial surface slightly concave, with few low protuberances and several short to long stiff setae; ventral surface generally convex, but anterior half forming shallow concavity to accommodate flexed palm. Merus with few tufts of short stiff setae on dorsal surface laterally, dorsodistal margin unarmed; lateral and mesial faces almost smooth, ventrolateral margin with 3 small spines in distal half, ventromesial margin unarmed but with row of short stiff setae and 1 capsule-like seta at midlength; ventral surface gently convex, with few long setae. Ischium unarmed, with few short stiff setae on surfaces. Coxa unarmed.

Left cheliped ( Figs. 1 C; 2C, D) moderately slender. Chela about 3.0 times longer than wide (greatest width at base of fingers). Dactylus about 1.3 times as long as palm; dorsomesial margin not delimited, surfaces nearly smooth, unarmed, with tufts of short to moderately long setae; cutting edge with row of minute, corneous teeth in distal 0.6, terminating in small corneous claw. Palm about 0.7 times as long as carpus; dorsal surface slightly elevated in midline, bearing several minute granules and sparse short setae; dorsolateral margin delimited by low, interrupted ridge not extending onto fixed finger, dorsomesial margin not delimited; lateral surface smooth; mesial surface with scattered short to long setae; ventral surface convex, with sparse long setae. Cutting edge of fixed finger with row of minute corneous teeth in distal 0.4. Carpus distinctly shorter than merus; dorsolateral margin with 2 small spines and few bristle-like setae, dorsomesial margin with row of bristle-like setae and 1 small spine located at midlength; lateral surface with few short setae dorsally, ventrolateral distal angle with 1 tiny spine; mesial surface with scattered long setae; ventral surface convex, with few long setae. Merus with few tufts of short stiff setae on dorsal surface, dorsodistal margin unarmed; lateral face smooth, ventrolateral margin with 3 small spines in distal 0.3; mesial face with stiff, sometimes bristle-like setae ventrally, ventromesial margin unarmed; ventral surface with few setae. Ischium unarmed, with few setae. Coxa unarmed.

Ambulatory legs (Fig. 3A, C) moderately long and slender, right second overreaching tip of extended right cheliped. Dactyli (Fig. 3B, D) very slender, 11 (second) or 14 (third) times longer than wide, about 1.1 (second) or 1.2 (third) times longer than propodus, in dorsal view straight, in lateral view nearly straight with slight curve in distal half; dorsal margins each with row of sparse setae becoming shorter distally; lateral and mesial faces nonsulcate; mesial faces unarmed (second) or armed with 1 minute corneous spinule dorsally (third); ventral margins each with 8 long, slender corneous spines. Propodi distinctly longer than carpi, slightly narrowing distally; dorsal surfaces each with moderately long stiff setae; lateral and mesial faces glabrous; ventral surfaces each with 2 widely spaced, slender corneous spines, distal margin with pair of slender corneous spines. Carpi unarmed dorsally, with few short setae on dorsal margin. Meri somewhat widened; dorsal and ventral margins spine-less, with few long stiff setae. Ischia unarmed. Female with unpaired left gonopore ( Fig. 1 E).

Fourth pereopods ( Fig. 1 D) semichelate. Dactyli nearly straight, each with row of minute corneous teeth on ventral margin, terminating in tiny corneous claw; no preungual process. Propodal rasp consisting of single row of small corneous scales.

Fifth pereopods chelate.

Third thoracic sternite with anterior margin slightly produced medially, unarmed. Sixth thoracic sternite ( Fig. 1 E) with anterior lobe transversely oblong, with row of moderately short setae on anterior margin. Eighth thoracic sternite composed of 2 rounded, widely separated lobes.

Pleon dextrally twisted. Female with 4 unpaired pleopods; second to fourth pleopods slightly unequally biramous, fifth much smaller than preceding pleopods, uniramous. Uropods markedly asymmetrical; protopods unarmed.

Telson ( Fig. 1 F) with slight lateral indentations slightly posterior to midlength; posterior lobes slightly asymmetrical, subtriangular, terminal margins slightly oblique, each with row of 3 or 4 spinules, posterolateral margins each with fringe of long setae.

Male unknown.

Coloration in life. Not known.

Distribution. Known only from the type locality, off Panglao Islands, the Philippines, at depths of 90– 100 m.

Remarks. Although only a single female specimen is available for study, the new species is assigned to Trichopagurus on the basis of strong similarities to T. asper and T. macrochela . In particular, the presence of a prominent fringe of long setae on the lateral margins of the posterior lobes of the telson is the character that is known so far only for species of Trichopagurus in the Paguridae ( Komai & Osawa 2005; Komai & Poupin 2012; personal observation).

Trichopagurus tenuidactylus n. sp. is closer to T. asper and T. macrochela in having a dorsoventrally flattened carpus of the right cheliped and the less setose ocular peduncles and ambulatory legs. The new species appears unique in the genus in having very slender dactyli of the third pereopods (about 14 times as long as wide versus less than 11 times as long). Furthermore, the relatively slender ultimate segment of the antennular peduncle, the smooth dorsal surface of the palm of the right cheliped and the presence of dorsomesial spines on the carpus of the right cheliped distinguish T. tenuidactylus n. sp. from T. asper (in the latter species, the right palm has scattered tubercles; the carpus of the right cheliped lacks dorsomesial spines). The new species differs from T. macrochela in having dorsal spines on the carpus of the left cheliped ( T. macrochela , with the carpus of the left cheliped unarmed on the dorsal surface).

The three previously known congeneric species have been all collected from intertidal to shallow subtidal depths in coral reefs ( Komai & Osawa 2005; Komai & Poupin 2012; this study), but the present new species is the first example of the genus collected from the sublittoral depths of 90– 100 m.

In the holotype, there is one capsule-like structure on the ventromesial margin of the merus of the right cheliped. The occurrence of similar capsule-like structure on the cheliped meri are known in T. asper , though Komai & Poupin (2012) presumed these structures might represent egg sacs of other invertebrates or parasites.

Etymology. From the combination of the Latin tenuis (= narrow) and dactylus (claw), in reference to the very slender dactylus of the third pereopods in the new species.

Figures

FIGURE 1. Trichopagurus tenuidactylus n. sp., holotype, ovigerous female (sl 1.4 mm), NMCR 39078. A, shield and cephalic appendages, dorsal view (left cornea shrunk; antennal flagella omitted); B, chela and carpus of right cheliped, dorsal view; C, chela and carpus of left cheliped, dorsal view; D, left fourth pereopod, lateral view; E, coxae of third pereopods and sixth thoracic sternite, ventral view; F, telson, dorsal view. Scale bars: 0.5 mm.