Pagurixus eminens, Komai & Miller & Malay, 2022

Komai, Tomoyuki, Miller, Allison K. & Malay, Maria Celia D., 2022, Three new species of pagurid hermit crabs (Decapoda: Anomura: Paguroidea) from the Northern Mariana Islands, Micronesia, Zootaxa 5099 (5), pp. 563-585 : 576-583

Pagurixus eminens n. sp.

( Figs. 9–13 )

Material examined. Holotype: SIO-BIC C14515, male (sl 1.7 mm), Guguan, station AKM-GUG-02, 17.3063°N, 145.8317°E, 0–5 m, 22 June 2015, snorkel, coll. A.K. Miller, field No. S 25737.4.

Paratypes. SIO-BIC C14258, 1 female (sl 1.8 mm), Sarigan, station AKM-SAR-01, 16.6977°N, 145.7727°E, 0–5 m, 24 June 2015, crab trap, coll. A.K. Miller, field No. S 25762.3; SIO-BIC C14516, 1 female (sl 1.8 mm), Agrihan, 18.45°N, 145.38°E, depth not recorded, 17 June 2015, crab trap, coll. A.K. Miller, field No. S 25684.5, DNA voucher .

Description. Gills biserial, 11 pairs.

Shield ( Fig. 9A ) 1.1 times as long as wide; anterior margin between rostrum and lateral projections gently concave; anterolateral margins sloping; dorsal surface slightly convex, with few tufts of short setae anterolaterally. Rostrum triangular, moderately produced, terminating acutely. Lateral projections obsolete, each with submarginal spinule.

Ocular peduncles ( Fig. 9A ) moderately long and stout, 0.7 length of shield, with few tufts of short stiff setae on dorsal surface mesially; cornea not dilated, corneal diameter about 0.3 of peduncular length; basal part not inflated, as wide as cornea. Ocular acicles subtriangular, each with submarginal spinule.

Antennular peduncles ( Fig. 9A–C ) stout, reaching distal corneal margin by tip of ultimate segment. Ultimate article 1.8 times longer than high, with prominent tuft of long setae on dorsolateral distal portion; ventral surface with 2 rows of short setae directed outward. Basal article with small laterodistal spine on statocyst lobe. Ventral flagellum with row of dense long setae directed outwards on lateral and mesial margins.

Antennal peduncles ( Fig. 9A ) reaching distal corneal margin by tip of article 5. Article 3 with small spine at ventromesial distal angle (not visible in dorsal view). Article 2 with spinule at dorsomesial distal angle; laterodistal projection short, falling far short of midlength of article 4, terminating in small spine. Article 1 with laterodistal spinule; ventromesial distal margin with small projection. Antennal acicles moderately long, slightly arcuate, reaching nearly to base of cornea, terminating in spine; mesial and lateral margins with sparse setae. Antennal flagella not reaching extended right cheliped; each article with few short setae on distal margin.

Maxilliped 3 ( Fig. 9D ) endopod moderately stout. Ischium with well-developed crista dentata consisting of row of minute corneous-tipped teeth and 1 accessory tooth. Merus and carpus unarmed. Exopod reaching midlength of carpus.

Male right cheliped ( Fig. 10A–D ) stout, not particularly elongate. Chela suboval, 1.5 times as long as wide. Dactylus subequal in length to palm measured along mesial margin, terminating in small corneous claw; dorsomesial or mesial margin not delimited; slightly rounded dorsal surface without conspicuous spines or tubercles, mesial surface slightly granular, ventral surface nearly smooth; cutting edge with 2 obtuse calcareous teeth in proximal 0.6 and row of minute, corneous teeth in distal 0.4. Palm not widened distally, slightly wider than long, 0.8 times as long as carpus; dorsal surface convex, slightly granular, no conspicuous spines or tubercles, with scattered sparse very short setae; dorsolateral and dorsomesial margins not delimited; lateral and mesial faces almost glabrous; ventral surface also smooth, gently convex, with few short setae. Fixed finger terminating in corneous claw; cutting edge irregularly dentate. Carpus subequal in length to merus, widened distally, length about 1.4 of distal width; dorsal surface sparsely granulate, only with few scattered short to moderately short setae, but without conspicuous spines; dorsodistal margin with few spinulose tubercles; lateral surface without trace of division, with coarse granules, ventrolateral margin with 1 small blunt tubercle distally; mesial face also with coarse granules, ventromesial margin faintly granulate; ventral surface convex, with few short setae. Meral-carpal articulation lacking any pronounced clockwise rotation. Merus unarmed on dorsodistal margin, dorsal surface also unarmed and glabrous; lateral and mesial faces also smooth, glabrous; ventrolateral margin armed with row of 3 small spines in distal 0.4; ventromesial margin faintly tuberculate; ventral surface gently convex, with sparse long setae. Ischium with smooth ventromesial margin; surfaces smooth, with few setae.

Female right cheliped ( Fig. 11A–D ) distinctly longer and stouter than left, proportionally more slender than male right cheliped. Chela subovate in dorsal view, 1.8 times longer than broad. Dactylus 1.2 times as long as palm, terminating in small corneous claw; dorsomesial margin not delimited; dorsal surface with nearly smooth; mesial face with tufts of short setae; ventral surface nearly smooth, with sparse short to long setae; occlusal margin with row of small corneous teeth. Palm about half-length of carpus; convex dorsal surface almost glabrous; dorsolateral margin delimited by distinct, granular ridge extending to midlength of fixed finger; dorsomesial margin not delimited; lateral face with sparse coarse granules; mesial face with few granules, ventral face convex, almost smooth, with few setae. Fixed finger terminating in small corneous claw; occlusal margin with few small calcareous teeth proximally and row of small corneous teeth in distal half. Carpus, merus and ischium generally similar to those of male right cheliped in armature; carpus length 1.6 times of width. Merus generally similar to that of male.

Left cheliped ( Fig. 10E–H ) moderately short, stout, distinctly shorter than right. Chela subovate in outline, approximately twice as long as wide, 1.1 times longer than carpus. Dactylus 1.3 times as long as palm, terminating in small corneous claw, with sparse tufts of short setae on surfaces; dorsal surface rounded, unarmed; occlusal margin with row of small corneous teeth increasing in length distally. Palm about half-length of carpus; dorsal surface with few granules; dorsolateral and dorsomesial margins not delimited; lateral surface with few short setae; mesial and ventral surfaces smooth; scattered long setae on ventral surface (including fixed finger). Fixed finger terminating in small corneous claw, occlusal margin with row of small corneous teeth. Carpus somewhat compressed laterally, slightly shorter than merus; length about twice of distal width and 1.7 of height; dorsolateral margin not delimited, dorsomesial margin with row of small spines or tubercles and bristle-like stiff setae; dorsodistal margin with small spine medially; lateral surface nearly perpendicular, without trace of division, bearing sparse granules, ventrolateral distal margin denticulate; mesial surface nearly smooth, ventromesial distal margin unarmed; ventral surface convex, with sparse long setae. Merus glabrous on dorsal surface, dorsodistal margin unarmed; lateral face almost smooth, ventrolateral margin with row of 3 small spines in distal 0.3; mesial face also smooth, ventromesial margin faintly tuberculate; ventral surface slightly with sparse long setae. Ischium unarmed.

Ambulatory legs ( Fig. 11E–H ) relatively stout, similar on right and left. Dactyli 0.8–0.9 times as long as propodi, 4.4–5.1 times longer than wide, terminating in large corneous claws; dorsal surfaces with few short setae; lateral and mesial faces glabrous, latter unarmed ( Fig. 11F, H ); ventral margins each with 5 moderately long corneous spines increasing in size distally. Propodi not tapering distally, 2.9–3.1 times longer than wide; dorsal surfaces with sparse moderately long setae; lateral and mesial faces smooth, glabrous; ventral margins each with 3–4 corneous spinules, ventrodistal margins each with single or paired small corneous spines. Carpi each with small dorsodistal spine, dorsal surfaces unarmed, with row of moderately long setae; lateral, mesial, and ventral faces glabrous. Meri with sparse setae on dorsal margins; lateral and mesial faces glabrous; ventrolateral distal margins unarmed, ventral margins spinulose (second) or slightly angular (third). Ischia with few (second) or row (third) of setae on dorsal margin; ventral margins with few setae. Females with unpaired gonopore on left coxa of pereopod 3.

Pereopods 4 ( Fig. 9E ) weakly semichelate, generally similar from right to left, although right slightly smaller. Dactylus moderately broad, straight, terminating in small corneous claw, with few short setae. Propodus with few setae on dorsal margin; mesial faces nearly flat or slightly convex, with few short setae, but without prominent tuft of setae; propodal rasp of single row of corneous scales. Carpus with several setae on dorsal margin.

Pereopods 5 chelate. Coxae of male ( Fig. 9F ) strongly unequal; right coxa with prominent ventromesial protrusion directed mesially and bearing prominent tuft of setae oriented mesially and exceeding well beyond lateral margin of left coxa; left coxa with gonopore anteriorly encircled by short to long setae, no protrusion of vas deferens seen.

Anterior lobe of thoracic sternite 6 ( Fig. 9G ) subrectangular, with row of sparse short setae on anterior margin. Thoracic sternite 8 ( Fig. 9F ) composed of two subequal, moderately separated, rounded lobes; each lobe bearing few short setae laterally to anteriorly.

Pleon without distinctive features; male with unpaired left pleopods 3–5; female with unpaired left pleopods 2–4.

Telson ( Fig. 9H ) with weak lateral indentation; posterior lobes rounded, terminal margins unarmed.

Colouration in life. Fig. 13 . Shield pale brown generally, with pair of darker spots posterior to bases of ocular acicles; posterior carapace yellowish translucent. Ocular peduncles also pale brown, with large darker blotch on dorsal surfaces. Antennular peduncle ultimate article brown, becoming paler proximally. Antennal peduncle article 2 dark brown; article 3 and 4 each with dark brown blotches on dorsal surface; article 5 with lateral and mesial margins brown, otherwise semi-translucent; flagella banded with white and brown (brown bands wider than white bands). Right cheliped chela and carpus dark brown on dorsal surface, merus distally dark brown in distal half, yellowish brown in proximal half. Left cheliped fingers yellowish white, palm dark brown on dorsal face; carpus and merus distally yellowish white and proximally dark brown. Pereopods 2 and 3 generally yellowish white with dark brown markings (see also Fig. 11G ); dactyli each with proximal ring; propodi each with middle ring; carpi yellowish white in distal 0.3, dark brown proximally in proximal 0.7; meri each with middle ring. Pleon entirely yellowish semi-translucent.

Distribution. Presently known only from the Northern Mariana Islands (Guguan, Sarigan and Agrihan), intertidal to shallow subtidal (5 m).

Etymology. From the Latin “eminens” (= prominent), in reference to the prominent ventromesial protrusion on the right coxa in males of the new species.

Remarks. Pagurixus is currently represented by 41 species, all of which are distributed in the Indo-West Pacific ( McLaughlin & Haig 1984; Komai & Osawa 2006; Komai 2010; Komai & Poupin 2013; Osawa et al. 2013; Komai et al. 2021). Most species occur in tropical or subtropical coral reefs, while some species are restricted to the temperate areas of Australia and New Zealand ( McLaughlin & Haig 1984; Gunn & Morgan 1992; Morgan 1993; de Saint Laurent & McLaughlin 2000; Komai & Osawa 2006; Komai 2010). The genus is informally divided into two species groups, viz., P. anceps Forest, 1954 and P. boninensis ( Melin, 1939) , based on the presence ( P. boninensis group) or absence ( P. anceps group) of setal rows on the ventral surface of the antennular peduncle ultimate article ( McLaughlin & Haig 1984; Komai & Osawa 2006). Pagurixus eminens n. sp. is referred to the subgroup B of the Pagurixus boninensis group, as diagnosed by Komai & Osawa (2006), because of the lack of a longitudinal ridge on the lateral surface of the left cheliped carpus. It is very similar to P. annulus Komai & Poupin, 2013 , presently known only from Europa Island in the Mozambique Strait, western Indian Ocean, in the morphology and the banded colour pattern of the chelipeds and ambulatory legs ( Komai & Poupin 2013). Pagurixus eminens n. sp. is distinguished from P. annulus by the possession of a prominent mesial protrusion on the coxa of the right pereopod 5 in the males and better developed tuft of setae arising from the distal margin of that protrusion; setae consisting the tuft are long, far overreaching lateral margin of the left coxa ( Fig. 9F ). In P. annulus , the right coxa of the pereopod 5 in the males is devoid of a mesial protrusion; setae on the right coxa are short and fewer, not reaching the left coxa ( Komai & Poupin 2013: fig. 2J). Another potential diagnostic character is the armature of the telson terminal margin. In P. eminens n. sp., the terminal margins of the telson are unarmed ( Fig. 9H ), rather than having a row of spinules on each terminal margin as in P. annulus (cf. Komai & Poupin 2013: fig. 2K). The colour pattern of the chelipeds and ambulatory legs are generally similar between the two species, but details are still different. In P. eminens n. sp., the carpus of the left cheliped is dark brown in the dorsal surface; the dark brown bands on the carpi of the ambulatory legs extend to the proximal margins on the dorsal surfaces ( Fig. 13 ). In contrast, in P. annulus , the carpus of the right cheliped is clearly bi-coloured with the distal half white and proximal half darkly coloured; the bands on the carpi of the ambulatory legs are medial, not extending to the proximal end of the article ( Komai & Poupin 2013: figs. 1B, 2C). In addition, it is remarkable that there are not specimens referable to either P. annulus or P. eminens n. sp. in intervening localities despite the recent active collections (cf. Komai 2010; Osawa et al. 2013; Komai & Rahayu 2013; Komai et al. 2021).

Pagurixus brachydactylus Komai & Osawa, 2006 , presently known only from the Ogasawara Islands, Japan and P. pseliophorus Komai & Osawa, 2006 , known from the Japanese mainland and the Ryukyu Islands, are also similar to P. eminens n. sp., particularly in the absence of dorsomesial spines on the male right cheliped carpus and the relatively short dactyli of the pereopods 2 and 3. The colour pattern of the chelipeds and ambulatory legs are also similar among the three species, in particular, P. pseliophorus and P. eminens n. sp. are very similar to one another in this regard. Pagurixus brachydactylus differs from the present new species in the lack of a ventromesial protrusion on the right coxa of the pereopod 5 in the male (cf. Komai & Osawa 2006: fig. 26M). The male cheliped palm and carpus are more coarsely granular in P. brachydactylus than in P. eminens n. sp. ( Komai & Osawa 2006: fig. 27A–C versus Fig. 10A–D ). The pereopods 4 exhibit sexual dimorphism in the size and setation in P. brachydactylus ; in males, the pereopods 4 is subequal in the size and similar from right to left, whereas in females, they are unequal and dissimilar in the setation ( Komai & Osawa 2006: fig. 26D–K). In P. eminens n. sp., the pereopods 4 are not sexually dimorphic; subequal and similar in the setation. The dactylus of the left pereopod 3 is distinctly shorter than the propodus in P. brachydactylus (cf. Komai & Osawa 2006: fig. 28B), rather than subequal in length to the latter article in P. eminens n. sp. ( Fig. 11D ).

Pagurixus pseliophorus is distinguished from P. eminens n. sp. by the following particulars. The shield is relatively narrower in P. pseliophorus than in P. eminens n. sp. (1.2–1.3 times as long as wide versus 1.0–1.1 times as long) ( Komai & Osawa 2006: fig. 36A versus Fig. 9A ). The palm of the male right cheliped is subequal in the length to the carpus in P. pseliophorus (cf. Komai & Osawa 2006: fig. 37A–D), whereas it is shorter than the latter in P. eminens n. sp. ( Fig. 10A–D ). The dactyli of the pereopods 2 and 3 are distinctly shorter than the propodi and relatively stout in P. pseliophorus (cf. Komai & Osawa 2006: 39), rather than subequal in the length to the latter article and relatively slender in P. eminens n. sp. ( Fig. 11E–H ).

It should be noted that the known range of the new species is not far from the Southern Mariana Islands, where the paguroid fauna is relatively well documented ( Paulay et al. 2003; Malay et al. 2021).

Figures

FIGURE 9. Pagurixus eminens n. sp., holotype, SIO-BIC C14515, male (sl 1.7 mm).A, shield and cephalic appendages, dorsal view; B, distal two peduncular articles and flagella of left antennule, lateral view; C, distal peduncular article and ventral flagellum of left antennule, ventral view; D, left maxilliped 3, lateral view; E, left pereopod 4, lateral view; F, coxae of pereopods 5 and thoracic sternite 8, ventral view; G, thoracic sternite 6, ventral view; H, telson, dorsal view.

FIGURE 10. Pagurixus eminens n. sp., holotype, SIO-BIC C14515, male (sl 1.7 mm). A, right cheliped, mesial view; B, same, lateral view; C, same, chela, dorsal view; D, same, carpus, dorsal view; E, left cheliped, mesial view; F, same, lateral view; G, same, chela, dorsal view; H, same, carpus, dorsal view.

FIGURE 11. Pagurixus eminens n. sp. A–D, paratype, SIO-BIC C14516, female (sl 1.8 mm); E–H, holotype, SIO-BIC C14515, male (sl 1.7 mm). A, right cheliped, chela and carpus, mesial view (merus with damaged mesial face not illustrated); B, right cheliped, lateral view; C, same, chela, dorsal view; D, same, dactylus, dorsal view; E, right pereopod 2, lateral view; F, same, dactylus and distal part of propodus, mesial view; G, left pereopod 3, lateral view, showing pattern of markings; H, same, dactylus and distal part of propodus, mesial view.

FIGURE 12. A, Catapagurus tenuilamina n. sp., holotype, SIO-BIC C14512, male (sl 2.7 mm)., habitus in lateral view, showing living colouration; B, Nematopagurus marianicus n. sp., paratypes, 3 males (sl 2.2, 2.5, 2.8 mm), 1 female (sl 1.9 mm), SIO-BIC C14520, showing living colouration.

FIGURE 13. Pagurixus eminens n. sp., holotype, SIO-BIC C14515, male (sl 1.7 mm), habitus in dorsal view, showing living colouration.