Pagurixus dissimilis, Osawa, Masayuki & Komai, Tomoyuki, 2007

Osawa, Masayuki & Komai, Tomoyuki, 2007, A new hermit crab species of the Pagurixus anceps group (Crustacea: Decapoda: Anomura: Paguridae) from southern Japan, and supplemental notes on P. patiae Komai, 2006, Zootaxa 1627, pp. 41-51: 42-48

publication ID

http://doi.org/ 10.5281/zenodo.179306

publication LSID

lsid:zoobank.org:pub:6AF2463F-FB79-42BC-A687-A72D08D1B77C

persistent identifier

http://treatment.plazi.org/id/942D8781-FFCC-FF8A-B0A0-4CC2FB80FD28

treatment provided by

Plazi

scientific name

Pagurixus dissimilis
status

n. sp.

Pagurixus dissimilis  n. sp.

( Figs. 1 –3View FIGURE 1View FIGURE 2View FIGURE 3, 5View FIGURE 5 A, B)

Type material. Holotype: male (sl 1.6 mm), Maeda-misaki, Okinawa Island, Ryukyu Islands, 3 m, night, SCUBA diving, coll. Y. Fujita, 28 July 2002, CBM-ZC 9068.

Paratypes: 3 males (sl 0.9–1.6 mm), 1 female (sl 1.3 mm), 2 ovig. females (sl 1.1, 1.5 mm), collection data as in holotype, CBM-ZC 9069; 1 male (sl 0.9 mm), same locality as in holotype, 5 m, night, SCUBA diving, coll. Y. Fujita, 21 July 2002, CBM-ZC 9070; 1 male (sl 1.5 mm), Kashiwa-jima Islet, Kochi Prefecture, Shikoku, subtidal, SCUBA diving, coll. E. Myorin, 30 June 2005, CBM-ZC 9071.

Description. Shield ( Fig. 1View FIGURE 1 A) 1.1–1.2 times longer than broad; anterior margin between rostrum and lateral projections weakly concave; anterolateral margins sloping; posterior margin roundly truncate; dorsal surface with few tufts of short setae laterally. Rostrum triangular, distinctly overreaching lateral projections, moderately slender, terminating in spinule. Lateral projections obtuse, each with submarginal spinule.

Ocular peduncles ( Fig. 1View FIGURE 1 A) moderately stout, 0.5–0.6 length of shield, each with row of tufts of short setae on dorsomesial surface; basal part inflated, slightly larger than corneal width; corneas not dilated or weakly dilated, corneal width about 0.3 of peduncular length. Ocular acicles subtriangular, each with small submarginal spine.

Antennular peduncles ( Fig. 1View FIGURE 1 A, B) overreaching distal margins of corneas by 0.2–0.3 lengths of ultimate segments. Ultimate segment without tuft of long setae at dorsolateral distal angle; ventral surface with few very short setae but lacking distinct rows of setae. Basal segment with spinule on distal margin of statocyst lobe. Ventral flagellum with few short setae on lateral and mesial margins.

Antennal peduncles ( Fig. 1View FIGURE 1 A) overreaching distal margins of corneas by 0.2–0.3 lengths of ultimate segments. First segment with small laterodistal spine. Second segment with laterodistal projection relatively short, barely reaching midlength of fourth segment, terminating in bifid spine; dorsomesial angle slightly produced but unarmed. Third segment with small spine at ventrodistal angle. Fourth and fifth segments unarmed. Antennal acicle relatively short, arcuate, overreaching proximal margin of, to slightly overreaching distal margin of, cornea, terminating in small spine; mesial margin with row of tufts of sparse setae. Flagellum moderately long, 2.0–3.0 times longer than shield.

Right cheliped of male ( Fig. 2View FIGURE 2 A –E) massive, much larger than left. Chela subovate in dorsal view, 1.8–1.9 times longer than broad. Dactylus 0.8–0.9 of palm length; dorsomesial margin delimited by blunt crest of short ridges; surfaces with short ridges bearing sparse short setae; dorsomesial surface weakly tuberculate or granular; cutting edge armed with 2 or 3 low calcareous teeth in proximal half and row of small corneous teeth in distal half, terminating in corneous claw. Palm 1.0– 1.1 times as long as carpus; convex dorsal surface covered with faint short ridges and low granules; granules on dorsomesial part larger; dorsolateral margin rounded; dorsomesial margin delimited by blunt or weakly crenulate longitudinal ridge; lateral, mesial and ventral surfaces also covered with faint short ridges and very small low tubercles. Fixed finger with weakly delimited dorsolateral margin; cutting edge armed with row of low calcareous teeth, terminating in corneous claw. Carpus 1.1–1.4 times longer than merus, 1.1–1.2 times as long as distal width and 1.3–1.4 length of greatest height, somewhat twisted laterally; dorsolateral margin not delimited; dorsomesial margin delimited by irregular row of 2–4 spines followed by short ridges bearing spiniform setae; dorsal surface with blunt but distinct median crest of row of short ridges, few small spines present on mesial proximal half; lateral surface with small low tubercles dorsally but lacking longitudinal ridge; ventral surface notably convex, bluntly ridged medially. Merus almost smooth on all surfaces; dorsal surface rounded; dorsodistal margin with sparse short setae; ventrolateral and ventromesial margins weakly protuberant proximally, bearing long setae; ventral surface flattish. Ischium with smooth ventromesial margin; surfaces unarmed.

Right cheliped of female ( Fig. 3View FIGURE 3 A –E) moderately stout for genus. Chela subovate in dorsal view, 1.9 –2.0 times longer than broad. Dactylus 1.1–1.3 times as long as palm; dorsal surface convex, with few short ridges; dorsomesial margin clearly delimited by row of short ridges or low protuberances; mesial and ventral surfaces with few short ridges; cutting edge armed with row of small corneous teeth, terminating in small corneous claw. Palm 0.6 length of carpus; weakly convex dorsal surface with small, low tubercles; dorsolateral margin delimited by blunt ridge extending nearly tip of fixed finger, dorsomesial margin delimited by row of short oblique ridges; lateral and mesial faces with faint, short ridges; fixed finger with row of small, acute calcareous teeth, terminating in small corneous claw. Carpus 0.8 –1.0 times as long as merus, length 1.5–1.6 times distal width and 1.7–1.8 times greatest height; dorsal surface with small tubercles and subacute protuberances laterally and with row of 3 or 4 spines followed by short ridges bearing spiniform setae mesially; dorsolateral margin not delimited; dorsomesial margin delimited by row of short ridges and small, blunt protuberances; lateral face nearly perpendicular, with small, low tubercles dorsally but devoid of distinct longitudinal ridge; ventral surface convex, protuberant. Merus smooth on dorsal, lateral, and mesial surfaces; ventrolateral margin with 1–3 small subdistal spines; ventromesial margin unarmed; ventral surface convex, slightly uneven. Ischium unarmed.

Left cheliped ( Fig. 2View FIGURE 2 F –I) moderately short and stout, generally similar between male and female. Chela 2.5–2.6 length of width. Dactylus 1.5–1.7 times longer than palm, with sparse tufts of setae on surfaces; dorsal and ventral surfaces smooth; mesial face with few small spines proximally; cutting edge armed with row of small corneous teeth, terminating in small corneous claw. Palm 0.4–0.5 length of carpus; dorsal surface convex, with crest of small spines and short elevated ridges on midline and with small, subacute and low tubercles laterally and mesially; dorsolateral margin delimited by blunt crest; dorsomesial margin weakly delimited by row of small, subacute and low tubercles; lateral, mesial and ventral surfaces nearly smooth, with scattered setae. Cutting edge of fixed finger armed with short row of small calcareous teeth interspersed with small corneous teeth, terminating in small corneous claw. Carpus somewhat twisted laterally, 0.8 length of merus; length 2.5 times distal width and 2.2–2.4 times greatest height; dorsolateral margin with 1 distal spine or row of 2–4 spines followed by short ridges bearing spiniform setae; dorsomesial margin with row of 3 or 4 spines; lateral face nearly perpendicular, with few setae but lacking trace of median ridge, ventrolateral distal margin unarmed; mesial face with short ridges bearing sparse setae adjacent to dorsomesial margin; ventral surface with sparse setae. Merus smooth on dorsal surface, dorsodistal margin unarmed; lateral and mesial faces also smooth; ventrolateral distal margin with 2–4 small spines; ventromesial margin with row of small tubercles; ventral surface weakly convex, smooth, with scattered setae. Ischium unarmed.

Ambulatory legs ( Fig. 3View FIGURE 3 F –L) moderately slender, generally similar from right to left, but right third propodus more slender and elongate than left third. Dactyli 0.8 –1.0 length of propodi, 4.7–6.1 times longer than high measured at proximal ends, terminating in large corneous claws; dorsal surfaces with sparse short setae; lateral and mesial faces with few short setae but unarmed; ventral margins each with 5–7 slender corneous spines increasing in size distally. Propodi not markedly tapering distally, 3.5 –5.0 times longer than high measured at proximal end; dorsal surfaces nearly smooth, with row of sparse short setae; lateral faces smooth; ventral margins each with 1–4 short or very short corneous spinules, ventrodistal margins each with paired corneous spines. Carpi each with small dorsodistal spine; dorsal surfaces each with 1 small spine and small protuberance in proximal half mesially (second) or 1 spinule in proximal 0.3 or unarmed (third), and bearing row of sparse short setae; lateral and mesial faces with few short setae; ventrodistal projection of left third obtuse. Meri generally smooth; dorsal and ventral margins each bearing row of sparse setae; lateral and mesial surfaces nearly smooth; ventrolateral distal margins each with small subdistal spine (second) or unarmed (third); ventromesial distal margin crenulated (second) or smooth (third).

Fourth pereopods ( Fig. 1View FIGURE 1 C –F) semichelate; size generally similar from right to left in males but distinctly unequal in females, at least left merus larger than right. Dactyli broad, each terminating in small corneous claw, bearing tuft of setae on dorsodistal margin, length of setae subequal from right to left in males but left setae much longer than right in females; ventral margin with row of minute corneous teeth. Propodi each with tuft of setae on dorsodistal margin; propodal rasp consisting of single row of small corneous scales; mesial face slightly convex. Carpi with sparse tufts of setae on dorsal and ventral faces.

Males with coxae of fifth pereopods slightly unequal ( Fig. 1View FIGURE 1 H); right with prominent tuft of comparatively short setae, only reaching midline of eighth thoracic sternite; papilla-like protrusion of vas deferens present. Left coxa with gonopore partially masked by tuft of short setae. Females with paired gonopores.

Anterior lobe of sixth thoracic sternite ( Fig. 1View FIGURE 1 G) subovate or oblong, with row of short setae on anterior margin. Eighth thoracic sternite ( Fig. 1View FIGURE 1 H) composed of two slightly unequal, closely set, rounded lobes (right lobe larger than left); anterior margin of each lobe with row of short setae.

Telson ( Fig. 1View FIGURE 1 I) with lateral indentations; lateral margins of posterior lobes bordered by chitinous edges; terminal margins oblique or nearly transverse, each with 3 or 4 spines.

Color in life ( Fig. 5View FIGURE 5 A, B). Shield pale brown, with 2 or 3 pairs of brown spots on anterior half. Posterior carapace whitish, with scattered small, brown spots. Ocular peduncles with 3 or 4 brown spots on dorsal surfaces, proximal spot largest. Antennular peduncles translucent; ultimate segments each with broad light brown ring distally and brown ring on subproximally; penultimate segments also each with brown ring distally. Antennal peduncles translucent, with scattered spots or dots. Right cheliped pale brown or white generally, with some irregular, brown spots or blotches on palm, carpus, and merus. Left cheliped also pale brown or white; palm with brown band or 2 spots proximally; carpus with brown transverse bands medially and proximally; merus also with median band. Ambulatory legs with brown transverse bands on translucent white background; dactyli each with 1 proximal band; propodi each with 2 bands, one at middle, another at proximal; carpi each with 3 irregular markings; meri each with 2 bands (brown color apparent on margins) subdistally and subproximally.

Variation. Komai (2006) indicated that the possession of markedly unequal fourth pereopods was diagnostic for P. patiae  among species of the P. anceps  group. In the present new species, the morphology of the fourth pereopods appears different between males and females. In males, the fourth pereopods are generally similar from the right to the left, whereas in females, they are markedly unequal and dissimilar, of which only the left is provided with a distinct tuft of long setae on the dactylus. Although the sample size is limited, we suggest that this difference may be the result of sexual dimorphism.

Etymology. The specific name is a combination of the Latin, dis (not) and similis (similar), in reference to the different morphology of the fourth pereopods between males and females.

Distribution. Kashiwa-jima Islet in Shikoku and Okinawa Island in the Ryukyu Islands, southern Japan, at depths of 3– 5 m.

Remarks. The new species belongs to the P. anceps  group because of the lack of the setal rows or series on the ventral surface of the ultimate segment of the antennular peduncle ( Komai & Osawa 2006). Pagurixus dissimilis  n. sp. appears closest to P. nanus  in both morphology and coloration in life. The two species have one or two small spines on the proximal half of the dorsal surface of each carpus of the second pereopods. The other species of the P. anceps  group lack such spines on the carpi of the second pereopods. Pagurixus dissimilis  is distinguished from P. nanus  by having a clearly delimited dorsomesial margin on the dactylus of the right cheliped in males and females, a blunt but distinct median crest and small mesial spines on the dorsal surface of the carpus of the male right cheliped, and paired gonopores in females (an unpaired left gonopore is present in P. nanus  ). As mentioned above, the fourth pereopods of females are notably unequal and dissimilar in the new species, whereas they are subequal and similar in P. nanus  . Details of the coloration in life are also different between the two species. Pagurixus dissimilis  has irregular brown blotches or transverse bands on the carpi of the chelipeds, instead of scattered pink spots in P. nanus  .

As well as the new species, the brown-banded color pattern of the ambulatory legs is also seen in P. anceps  and P. patiae  , and therefore, these species can be easily confused without detailed observation on morphological characters. In addition to the possession of one or two subproximal spines on the dorsal surface of each carpus of the second pereopods, the presence of dorsomesial proximal spines on the carpus of the male right cheliped immediately distinguishes P. dissimilis  from the latter two species. The new species further differs from P. anceps  in having an obtuse ventrodistal margin of the carpus of the left third pereopod. In P. anceps  , the ventrodistal margin is distinctly produced. Pagurixus dissimilis  is separated from P. patiae  also by the dactylus of the right cheliped with a clearly delimited dorsomesial margin, the carpus of the male right cheliped with a distinct median crest and a mesial row of small spines on the dorsal surface, the proportionally longer dactyli of the ambulatory legs (0.8 –1.0 of the propodi length in P. dissimilis  versus 0.7–0.8 in P. patiae  ), and the paired gonopores in females (only an unpaired left gonopore is present in P. p a t i a e). Details of the coloration in life are also different between the two species. The transverse bands on the ambulatory legs of P. dissimilis  are usually broader and lighter in color than those of P. p a t i a e.