Petrolisthes uruma, Osawa, Masayuki & Uyeno, Daisuke, 2013

Osawa, Masayuki & Uyeno, Daisuke, 2013, A new subtidal species of the genus Petrolisthes Stimpson, 1858 (Crustacea: Decapoda: Porcellanidae) from Okinawa, with an account of species of the genus known from the Ryukyu Islands, southwestern Japan, Zootaxa 3670 (3), pp. 329-338 : 330-335

Petrolisthes uruma sp. nov.

( Figs. 1–3 )

[New Japanese name: Uruma-isokanidamashi]

Type material. Holotype ovigerous female (cl 8.3 mm), off mouth of Tengan River, Tengan, Uruma , Okinawajima Island, 10 m, 15 April 2012, collected by D. Uyeno, RUMF-ZC 2121.

Description. Carapace ( Fig. 1 A) as long as broad; dorsal surface flattish, with sparse, stiff short setae on anterior margins of striae and ridges; frontal and gastric regions with numerous, short transverse striae; hepatic, anterior branchial, and cardiac regions with scattered, very short striae or small pits bearing few short setae; posterior branchial regions with short and long oblique ridges; intestinal region punctate; protogastric ridges blunt but distinct; cervical grooves shallow; short epibranchial spine present near anterior end of each cervical groove; no other spines on margins or surface. Branchial margins strongly convex, broadest on posterior one third, each demarcated by longitudinal crest. Rostrum ( Fig. 1 B) relatively broad, weakly trilobate; median lobe bent ventrally, strongly produced, rounded on anterior margin; anterior margins of lateral lobes oblique; distinct dorsomedian groove extending onto protogastric ridges. Orbits shallow; supra-orbital margins somewhat elevated, faintly convex; outer orbital angles each terminating in small blunt projection.

Pterygostomial flap with longitudinal ridges bearing sparse short plumose setae; anterior margin narrowly rounded ( Fig. 1 G).

Third thoracic sternite ( Fig. 1 C) with ventral surface flattish; anterior margin trilobate, with row of short setae; median lobe broad, subtriangular; lateral lobes narrowly rounded, slightly exceeding apex of median lobe. Fourth thoracic sternite with pair of long striae bearing sparse short setae along concave anterior margin.

Ocular peduncles ( Fig. 1 F) large; dorsal surface with short and long striae on proximal part; dorsodistal extension onto cornea rounded, with row of very short striae bearing sparse short setae.

Basal article of antennular peduncles ( Fig. 1 E) slightly longer than broad; ventral surface weakly convex, with long, granulate transverse ridge on mediolateral part and some short transverse ridges on anterolateral part; anterior margin thin, with row of minute tubercles, mesial and lateral angles with small subtriangular and bifid projections, respectively; lateral margin somewhat concave anteriorly.

Antennal peduncles ( Fig. 1 F, G) moderately short, with second to fourth articles freely accessible to orbit and bearing sparse short setae on surfaces and margins. First article broad, with blunt spine at anterodistal angle. Second article with distinct laminate lobe on anterior margin, lobe slightly tuberculate and with small blunt spine at anteroproximal angle; dorsal and ventral surfaces nearly smooth. Third article transversely subrectangular; anterior surface with small protuberances and short blunt ridges; dorsal surface with few oblique ridges on proximal half; ventral surface with long ridge anterior to midline. Fourth article short, with few short arcuate striae.

Third maxilliped ( Fig. 1 H) with coxa bearing small distal projection on ventral margin, distomedian projection with blunt ridge basally but not articulated (not illustrated). Basis not fused with ischium, triangular (not illustrated). Ischium broad, subovate; lateral surface with oblique, short and long ridges and longitudinal ridge along dorsal margin; dorsodistal projection rounded. Merus with subtriangular lobe on ventral margin, distal margin of lobe blunt; lateral surface with oblique or transverse ridges. Carpus with small subtriangular projection on proximal part of ventral margin; lateral surface with short and long ridges, dorsal-most ridge longest and prominent. Propodus somewhat tapering distally, lateral surface nearly smooth. Dactylus short, subtriangular, nearly smooth on lateral surface. Merus to dactylus with row of very long setae on ventral margin. Exopod with proximal article small, rounded; distal article thin, relatively narrow, somewhat inflated on proximal part, reaching nearly to midlength of carpus, with short ridges on dorsal surface; flagellum well developed.

Chelipeds ( Fig. 2 A, B) subequal in size and similar in shape, flattened; dorsal surface moderately convex; ridges on all segments each with row of short plumose setae on anterior margin. Merus with short and long transverse ridges on dorsal and ventral surfaces, dorsoposterior surface with 1 small median spine, anterior margin with rounded distal lobe bearing small blunt spine, dorsodistal margin with 2 small spines on posterior half, ventrodistal margin with 1 sharp spine at anterior end. Carpus 2.1–2.2 times as long as broad; dorsal surface with shallow sulcus along posterior margin and with numerous, arcuate or transverse, marginally beaded ridges, those on midline long and pronounced; dorso-anterior margin with 3 broad teeth marginally crenulated and each terminating in small spine; dorsoposterior margin with row of 5 sharp spines on distal two thirds; ventral surface with interrupted transverse ridges; ventro-anterior margin slightly crenulated. Chela relatively narrow, 3.2–3.3 times as long as broad, 2.0 times longer than carpus; dorsal surface covered with oblique, arcuate, marginally beaded ridges, those on flexor side of midline very long; extensor margin gently convex, thin, with few short stiff setae near proximal end but no spines; ventral surface flattish on extensor half and convex on flexor half, with numerous, interrupted oblique ridges, flexor distal part with irregular rows of small tubercles. Palm with dorsomedian longitudinal crest obsolete; dorsoflexor margin delimited by row of short oblique ridges. Fingers without hiatus when closed; fixed finger with small, curved distal claw, cutting edge nearly straight, with row of small rounded teeth. Dactylus 0.4 length of chela, opening at slight oblique angle, with small, curved distal claw; dorsal surface with arcuate, marginally beaded ridges; dorso-extensor (posterior) margin weakly elevated, delimited by row of short ridges; cutting edge nearly straight, with row of small rounded teeth; ventral surface with short arcuate ridges; ventral cutting region weakly concave, with scattered short plumose setae.

Ambulatory legs (second to fourth pereopods, right second and left fourth missing; Fig. 2 C–G) moderately slender; third pereopod longest, fourth pereopod shortest. Meri somewhat compressed laterally, oblong, merus of second pereopod 1.0 and 1.1 lengths of meri of third and fourth pereopods, respectively; dorsal margin with row of 3–5 spines and plumose setae; lateral surface with numerous, interrupted transverse ridges each bearing row of short plumose setae and few short stiff setae (second and third pereopods) or row of short stiff setae and sparse long setae (fourth pereopod), lateroventral margin distally with 1 strong spine (second and third pereopods) or unarmed (fourth pereopod); laterodistal margin with minute, subacute or blunt spine (second and third pereopods) or unarmed (fourth pereopod) at ventral angle; ventral surface with few stiff setae; mesial surface with short transverse ridges, mesioventral distal margin unarmed on all 3 pereopods ( Fig. 2 D). Surfaces and margins of carpi, propodi, and dactyli with sparse, short and long stiff setae. Carpi moderately long; lateral surface with long blunt ridge dorsal to midline and with oblique ridges ventrally; dorsal margin with sharp distal spine (second pereopod) or unarmed (third and fourth pereopods); mesial surface with some oblique ridges; ventrodistal margin rounded. Propodi 5.2–5.3 times as long as broad, not tapering distally; lateral and mesial surfaces with scattered, short and very short ridges; dorsal margin faintly uneven; ventral margin with 3 or 4 corneous slender spines including paired spines on ventrodistal margin, distolateral spine largest. Dactyli ( Fig. 2 E) 0.5–0.6 lengths of propodi, each terminating in slightly curved claw; dorsal margin gently arched; ventral margin with 3 corneous slender spines decreasing in size proximally.

Fifth pereopod missing.

Pleon with tufts of short and long plumose setae on lateral margins; external surface with row of scattered, short and long stiff setae each along anterior and posterior margins of first to fourth segments and with sparse short setae on fifth and six segments. Telson ( Fig. 1 D) much broader than long, composed of 7 calcified plates; external surface with scattered short striae.

Female with pairs of developed pleopods on third to fifth abdominal segments, fifth pairs largest. Male unknown.

Coloration in life ( Fig. 3 ). Carapace and abdomen generally light brown, with numerous dark brown markings. Thoracic sternites pale orange. Telson reddish brown, with light brown small spots. Antennal peduncles with dark brown blotches. Third maxilliped reddish brown on lateral surface; ischium and merus with irregular, greenish brown markings; carpus with dark brown stripes on dorsal surface; dactylus orange distally, ventral long setae pale brown. Chelipeds dark reddish brown on dorsal surface and crimson on ventral surface, tips of dorsoanterior teeth of carpus and fingers white, ventral ridges of carpus and extensor margin of chela light brown, proximal part of cutting edge of dactylus orange, short plumose setae on ridges pale brown. Ambulatory legs light brown on surfaces; merus with dark brown blotches except for distal one third and dorsomedian parts on lateral surface and with irregular dark brown blotches on mesial surface; carpi with crimson band each on proximal and distal parts of lateral surface, ventral surface also crimson; propodi with crimson ring each on proximal and subdistal parts, proximal ring much narrower than subdistal, both rings combined on ventral surface; dactyli also with broad crimson ring proximally.

Habitat. The holotype was collected from the underside of one of large limestones (about 0.8 m in the major axis) on muddy slope, at the depth of 10 m.

Distribution. Known only from Okinawa-jima Island, Ryukyu Islands, southwestern Japan.

Etymology. The specific name “ uruma ” corresponds to the Ryukyuan language for “coral island,” which literally means Okinawa or Ryukyu Islands, the type locality of the new species. The name is used as a noun in apposition.

Remarks. Petrolisthes uruma sp. nov. most closely resembles P. moluccensis ( De Man, 1888) in having the following morphological characters: carapace with a pair of epibranchial spines but no supraocular and branchial marginal spines, weakly trilobate rostrum, chelae each without distinct row of plumose setae on extensor margin, and meri of ambulatory legs each with a row of spines on dorsal margin (cf. Osawa & Chan 2010). However, the new species is distinguished from P. moluccensis by the weak and short, transverse striae on the gastric and anterior branchial regions of the carapace (distinct and long striae in P. moluccensis ), the carpus of the cheliped is proportionally longer (2.1–2.2 times as long as broad, instead of 1.4–1.5 times in P. moluccensis ) and is armed with three acutely pointed teeth on the dorso-anterior margin (four or five, usually blunt teeth in P. moluccensis ), and the meri of the second and third pereopods have a much stronger spine at the lateroventral distal angle. In addition to these morphological differences, the two species are also discriminated by the coloration and habitat. The carapace is light brown with dark brown markings in P. uruma sp. nov.; instead of purplish, greenish, or yellowish brown, with irregular red or dark brown spots in P. moluccensis . The dorsal surface of the chelipeds of P. uruma sp. nov. is dark reddish brown, but that of P. moluccensis has the same coloration as on the carapace ( Osawa & Chan 2010; personal observation). Petrolisthes uruma sp. nov. is found to inhabit under large limestones on subtidal muddy slope, whereas P. moluccensis occurs in the crevices of dead coral blocks on intertidal or subtidal coral reefs (personal observation).

Petrolisthes boscii ( Audouin, 1826) is also similar to P. uruma sp. nov. in the general shape and ornamentation of the carapace and chelipeds, but it is immediately distinguished by the presences of distinct transverse or subarcuate striae on the carapace and pronounced dense tufts of short plumose setae ventrally on the gape of fingers of the cheliped and the absence of dorsal spines on the meri of the ambulatory legs.

Figures

FIGURE 1. Petrolisthes uruma sp. nov., holotype, ovigerous female (cl 8.3 mm), RUMF-ZC 2121. A, carapace and ocular and antennal peduncles, dorsal view (setae omitted from right side); B, rostrum, anterodorsal view; C, third and fourth thoracic sternites, ventral view (setae omitted from left side); D, telson, external view; E, basal article of left antennular peduncle, ventral view; F, anterior part of carapace and left ocular and antennal peduncles, dorsal view; G, second to fourth articles of left antennal peduncle and anterior part of pterygostomial flap, ventral view; H, left third maxilliped, lateral view (exopod not illustrated, ventral long setae omitted). Scales equal 1.0 mm.

FIGURE 2. Petrolisthes uruma sp. nov., holotype, ovigerous female (cl 8.3 mm), RUMF-ZC 2121. A, right cheliped, dorsal view (short plumose setae on ridges omitted); B, same, ventral view (short plumose setae on ridges omitted); C, left second pereopod, lateral view (short plumose setae on ridges of merus mostly omitted); D, same, distal part of merus, mesial view; E, same, dactylus and distal part of propodus, lateral view (setae omitted); F, left third pereopod, lateral view (setae omitted); G, right fourth pereopod, lateral view (long stiff setae on merus only illustrated). Scales equal 1.0 mm.

FIGURE 3. Petrolisthes uruma sp. nov., holotype, ovigerous female (cl 8.3 mm), RUMF-ZC 2121. Fresh specimen. A, entire animal, dorsal view (right second and left fourth pereopods missing); B, same, ventral view.