Polyonyx boucheti, Osawa, Masayuki, 2007

Osawa, Masayuki, 2007, Porcellanidae (Crustacea: Decapoda: Anomura) from New Caledonia and the Loyalty Islands, Zootaxa 1548, pp. 1-49 : 39-44

Polyonyx boucheti n. sp.

( Figs 13 –15)

Type material. Loyalty Islands. Lifou Island. Santal Bay. Atelier LIFOU. St. 1446 (St. 41B), Mepinyo, 20°50.8’S, 167°09.7’E, 36–40 m, 16 Nov. 2000, ovig. female CL 2.5 mm, holotype (MNHN-Ga 5714). Same data as holotype, 1 female CL 2.1 mm, paratype (MNHN-Ga 5715). St. 1434 (St. 12), Huca Htighé Island, 20°52.5’S, 167°08.1’E, 5–20 m, 6 Nov. 2000, 1 female CL 2.3 mm, paratype (MNHN-Ga 5716).

Description. Carapace ( Fig. 13 A) transversely ovate, 1.3–1.4 times as broad as long, broadest on median branchial margin. Dorsal surface weakly convex, entirely covered with delicate, short and moderately long, transverse striae bearing sparse minute setae on anterior margin. Rostrum ( Fig. 13 B) broad, not produced beyond eyes, nearly transverse in dorsal view, with sparse moderately long setae along anterior margin; weakly bent ventrally, trilobate in frontal view, median lobe broadly rounded, slightly extending laterals, without median longitudinal groove; lateral lobes low, rounded. Orbits ( Fig. 13 A) shallow; supra-orbital margins oblique; outer orbital angles rounded. Protogastric ridges and cervical grooves weakly demarcated. Hepatic region with scattered short setae, hepatic margin weakly convex. Branchial margins strongly convex, median part somewhat constricted; anterior margin with distinct crest; posterior margin and adjacent region with long, transverse ridges. Cardiac region striate.

Pterygostomian flaps ( Fig. 13 C) entire, with median, longitudinal, undulated ridge, shallowly concave on anterior dorsal part; anterior terminating in acute apex; anterior dorsal margin unarmed.

Third thoracic sternite ( Fig. 13 D) somewhat depressed medially; anterior margin trilobite, with sparse long setae; median lobe very broad, weakly convex on median anterior margin; lateral lobes narrow, distinctly exceeding median lobe, each with rounded apex. Fourth thoracic sternite with transverse series of setae along concave, anterior margin.

Telson ( Fig. 13 E) composed of 7 plates; proximolateral plates much smaller than others; distal plates moderately elongate.

Ocular peduncles ( Fig. 13 A, G) small, with 2 transverse striae on dorsal surface; dorsal extension onto cornea rounded.

Basal article of antennular peduncles ( Fig. 13 F) unarmed; anterior surface concave, weakly rugose; anterior, dorsal and ventral margins weakly tuberculate; ventral surface with transverse ridge on median lateral part; lateral margin with row of sparse setae.

Antennal peduncles ( Fig. 13 G) short, slender, nearly smooth, unarmed. First article largest, strongly produced forward in lateral view, broadly in contact with lower orbital margin, with longitudinal ridge along ventral margin; lateral surface concave; anterior margin narrowly rounded. Second and third articles roundly rectangular, third article elongate. Fourth article short, rounded.

Third maxilliped ( Fig. 13 H) with coxa bearing small subtriangular projection on distoflexor margin; distomedian projection not articulated. Basis articulating with ischium, rounded subtriangular. Ischium broad, ovate, with few delicate striae on ventral surface, with longitudinal ridge along extensor margin; anterior extensor projection broad, roundly subtriangular. Merus with laminate, broad, rounded lobe on ventroflexor margin, margin of lobe with small denticles; ventral surface weakly striate. Carpus with subtriangular projection on median part of flexor margin and longitudinal rugae on extensor surface. Propodus elongate, weakly tapering distally, with weak rugae along extensor margin. Dactylus somewhat elongate, ovate. Merus to dactylus with long setae on flexor margin. Exopod with proximal article small, rounded; distal article laminate, robust, reaching distal margin of merus, with distal flagellum (not illustrated), proximal part inflated, distal part slender.

Chelipeds ( Fig. 14 A–E) somewhat unequal, subcylindrical, inflated, without distinct spines or teeth; dorsal surface covered with short delicate, oblique and transverse striae each bearing few minute setae on anterior margin; ventral surface with few short rugae. Larger cheliped ( Fig. 14 A–C) with ischium bearing scattered short setae; flexor margin weakly crenulate. Merus with rounded transverse crest submedially on dorsal surface; dorsoflexor margin with roundly subrectangular lobe distally; ventral distoflexor corner with small tuberculate spines. Carpus 1.6–1.8 times as long as broad; dorso-extensor margin rounded, with tuft of long setae on distal part; dorsoflexor margin with elevated lobe, weakly or moderately convex, few setae present; dorsodistal margin with broad, roundly subtriangular or rounded lobe on extensor part; ventral flexor margin slightly concave. Chela relatively narrow, elongate, 1.4–1.6 times as long as carpus, 2.8–3.1 times as long as high, lying on extensor side; dactylus opening at oblique angle; extensor margin crested, weakly convex, with small denticles and tubercles on distal 2/3 and with long simple setae entirely; dorsal surface adjacent to extensor margin also with scattered short and long, simple setae. Palm with dorsal surface convex, no distinct dorsomedian longitudinal ridge present; dorsoflexor margin with longitudinal rugose ridge; dorsoflexor distal part with broad, rounded projection extending onto dactylus; ventral surface with longitudinal crest proximally along midline, distal flexor part with few to several simple setae. Fixed finger with weakly or moderately curved distal claw; dorsal surface with scattered short simple setae, most numerous along cutting edge; cutting edge with row of small, rounded or subtriangular teeth, submedian tooth large; ventral surface with row of simple setae along cutting edge. Dactylus 0.4–0.5 length of chela, with moderately curved distal claw; dorsal surface with longitudinal ridge composed of minute tubercles along flexor margin and simple setae along cutting edge; cutting edge with small, rounded or subtriangular teeth on median margin and large rounded tooth on proximal margin; ventral surface with simple setae along cutting edge.

Smaller cheliped ( Fig. 14 D, E) almost identical to larger cheliped, except for: chela with denticles or spinules on distal 3/4 of extensor margin; cutting edges with smaller teeth, that of fixed finger with proximal, large, subtriangular tooth composed of small teeth; dactylus opening at more stronger angle, with more strongly crested, longitudinal ridge along flexor margin.

Ambulatory legs (Fig. 15A–E) relatively short, subcylindrical, with scattered, short and long, simple setae marginally; lateral surface nearly smooth except for short rugae on meri (especially on extensor half). Ischia with weakly calcified part along distal margin of mesial surface. Meri somewhat compressed lateromesially, elongated ovate, decreasing in size posteriorly; extensor margin unarmed but slightly crenulated, weakly convex; distoflexor margins of lateral and mesial surfaces without lobes or spines; mesial surface of first ambulatory leg with weakly calcified part along proximal margin. Carpi elongate, nearly smooth on surfaces; lateral surface with longitudinal row of few short striae on midline; disto-extensor and distoflexor corners unarmed, narrowly rounded. Propodi 1.4–1.7 times as long as dactyli, 2.4–3.2 times as long as high; extensor margin slightly crenulated; flexor margin with 3 corneous spines, distal paired spines subequal in size. Dactyli each terminating in strongly curved, bifurcate claws, flexor claw sharply pointed, much larger than extensor claw; flexor margin with 2 small corneous spines; spines with produced base, much smaller than terminal claw.

Fifth pereopods slender, chelate; propodus with numerous short simple setae and 1 or 2 hooked setae.

Female with no pleopods on third abdominal segments, but with well developed pleopods on fourth and fifth abdominal segments.

Polyonyx boucheti , holotype, ovig. female, CL 2.5 mm, Loyalty Islands, St. 1446. A, left first ambulatory leg, lateral view; B, same, ischium and merus, mesial view; C, same, dactylus and distal part of propodus, lateral view; D, left second ambulatory leg, lateral view (setae omitted); E, left third ambulatory leg, lateral view (setae omitted). Scales equal 1.0 mm.

Coloration. (Preserved in ethanol) Carapace with narrow, transverse and oblique, brown lines. Chelipeds with irregular, reticulated, brown markings. Ambulatory legs with no markings.

Etymology. The new species is dedicated to Dr. Philippe Bouchet of MNHN, who organized and was the head of the workshop done in Lifou Island.

Remarks. Polyonyx boucheti n. sp. is close to P. utinomii Miyake, 1943 . These two species share the following characters: carapace covered with delicate, long, transverse striae on the dorsal surface; rostrum without a distinct tuft of setae on the anterior margin; and dactyli of the ambulatory legs each with a bifurcate claw, flexor claw being much larger than the extensor. However, the present new species is distinguished from P. utinomii by the frontal margin of the carapace bearing long, simple setae (short setae in P. utinomii ), merus of the third maxilliped with the flexor lobe being marginally dentate (smooth in P. utinomii ), merus of the cheliped with a comparatively narrower, roundly subrectangular lobe on the dorsoflexor distal margin (broad, rounded lobe in P. utinomii ), and ambulatory legs bearing longer and more numerous setae (see Osawa 2001).

Distribution. Present known only from the Loyalty Islands, 5– 40 m.

Figures

FIGURE 13. Polyonyx boucheti n. sp., holotype, ovig. female, CL 2.5 mm, Loyalty Islands, St. 1446. A, carapace, and ocular and antennal peduncles, dorsal view; B, rostrum, anterior view; C, left pterygostomian flap, anterior part, lateral view; D, third and forth thoracic sternites, ventral view (setae omitted from left side); E, telson, extensor view; F, basal article of left antennular peduncle, ventral view; G, left anterior part of carapace, and ocular and antennal peduncles, dorsolateral view; H, right third maxilliped, ventral view (most setae omitted). Scales equal 1.0 mm.

FIGURE 14. Polyonyx boucheti n. sp., holotype, ovig. female, CL 2.5 mm, Loyalty Islands, St. 1446. A, larger cheliped, dorsal view; B, same, ventral view; C, same, chela, dorso-extensor view; D, smaller cheliped, dorsal view; E, same, chela, dorso-extensor view. Scales equal 1.0 mm.