Uroptychus inermis,

Baba, Keiji, 2018, Chirostylidae of the Western and Central Pacific: Uroptychus and a new genus (Crustacea: Decapoda: Anomura), Tropical Deep-Sea Benthos (Mémoires du Muséum national d'Histoire naturelle 212), pp. 1-612: 240-243

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Uroptychus inermis

n. sp.

Uroptychus inermis  n. sp.

Figures 109View FIGURE 109, 110View FIGURE 110

TYPE MATERIAL — Holotype: New Caledonia, Norfolk Ridge. BIOCAL Stn DW 36, 23°09’S, 167°11’E, 650-680 m, 29.VIII.1985, ♂ 4.7 mm ( MNHN-IU-2014-16584).GoogleMaps 

ETYMOLOGY — From the Latin inermis  (unarmed), alluding to the P 1 ischium without subterminal spine, a character to separate the species from U. granulipes  n. sp.

DISTRIBUTION„ Norfolk Ridge; 650- 680 m.

DESCRIPTION„ Carapace: As long as broad; greatest breadth measured at posterior third, 1.5 × distance between anterolateral spines. Dorsal surface slightly convex from anterior to posterior, finely granulated on anterior portion and branchial region; small hepatic spine on right side only. Lateral margins slightly convex, sparsely setose, with granulate scale-like ridge at anterior end of branchial margin followed by very fine granulations, posterior quarter with low ridge; anterolateral spine well developed, extending far beyond much smaller lateral orbital spine, situated slightly posterior to level of that spine. Rostrum broadly triangular, with interior angle of 30 °, nearly horizontal, about half as long as remaining carapace, breadth half carapace breadth at posterior carapace margin; dorsal surface moderately concave. Lateral orbital spine separated from anterolateral spine by basal breadth of latter spine. Pterygostomian flap smooth on surface, anterior margin angular, produced to sharp spine.

Sternum: Excavated sternum ending in sharp spine between bases of Mxp1, surface with small spine in center. Sternal plastron slightly broader than long, successively broader posteriorly. Sternite 3 depressed well; anterior margin of broad V-shape with narrow U-shaped median sinus flanked by well-developed spine. Sternite 4 with convex anterolateral margin anteriorly blunt angular, without spine, posterolateral margin half as long as anterolateral margin. Anterolateral margin of sternite 5 strongly convex, 1.3 × longer than posterolateral margin of sternite 4

Abdomen: Somites smooth and glabrous. Somite 1 moderately convex from anterior to posterior. Somite 2 tergite 2.8 × broader than long; pleuron posterolaterally blunt angular, lateral margin shallowly concave and weakly divergent posteriorly. Pleuron of somite 3 posterolaterally blunt. Telson about half as long as broad; posterior plate twice as long as anterior plate, moderately emarginate on posterior margin.

Eye: 1.7 × longer than broad, reaching distal quarter of rostrum; mesial margin feebly concave proximal to cornea. Cornea not inflated, distinctly more than half as long as remaining eyestalk.

Antennule and antenna: Ultimate antennular article 2.3 × longer than high. Antennal peduncle slightly overreaching cornea. Article 2 distolaterally acuminate, without distinct spine. Antennal scale 1.6 × broader than article 5, slightly falling short of distal end of article 5. Distal 2 articles unarmed; article 5 1.8 × longer than article 4, breadth less than half height of antennular ultimate article. Flagellum of 19 segments terminating in distal end of P 1 merus.

Mxp: Mxp1 with bases close to each other and slightly separated. Mxp3 sparsely setose. Basis with 3 denticles on mesial ridge. Ischium with about 20 denticles on crista dentata; flexor margin not rounded distally. Merus 2.2 × longer than ischium, somewhat ridged along flexor margin bearing a few very small obtuse protuberances. Carpus unarmed.

P 1: Relatively massive, barely setose except for fingers; length 4.4 × that of carapace. Ischium with compressed, triangular dorsal spine, without ventromesial subterminal spine. Merus somewhat granulose dorsally; ventral and mesial surfaces with finely granulate ridges continued on to carpus; length slightly more than that of carapace. Carpus slightly longer than merus, as long as palm, granulose like merus. Palm convex on dorsal and ventral surfaces, smooth and nearly glabrous, length 2.4 × breadth. Fingers setose (setae not very long), moderately curving ventrally, distally incurved, crossing when closed; movable finger 0.6 × as long as palm, opposable margin with rounded process about at midlength with accompanying smaller process proximal to it, larger process fitting to concavity on opposable face of fixed finger when closed; opposable margin of fixed finger with 2 low prominences medially.

P 2-4: Relatively slender, moderately compressed mesio-laterally, barely setose on meri, sparsely so on carpi and propodi, more setose on dactyli. Left P 2 and P 3 detached from body and missing. Meri successively shorter posteriorly ( P 3 merus 0.9 × length of P 2 merus, P 4 merus 0.8 × length of P 3 merus), equally broad on P 2-4; dorsal margin unarmed; length-breadth ratio, 5.3 on P 2, 4.9 on P 3, 4.0 on P 4; P 2 merus 0.9 × length of carapace, 1.3 × length of P 2 propodus; P 3 merus as long as P 3 propodus; P 4 merus 0.8 × length of P 4 propodus. P 2-3 carpi subequal, P 4 carpus 0.9 × length of P 3 carpus; carpus-propodus length ratio, 0.51 on P 2, 0.47 on P 3, 0.42 on P 4. Propodi shortest on P 2, subequal on P 3 and P 4; flexor margin nearly straight, ending in pair of spines preceded by 4 spines on P 2 and P 3, 3 spines on P 4 at most on distal half, distalmost of these spines more remote from distal pair than from distal second. Dactyli subequal in length, shorter than carpi (dactylus-carpus length ratio, 0.9 on P 2 and P 3, 0.95 on P 4), less than half length of propodi (dactylus-propodus length ratio, 0.4 on P 2-4); flexor margin gently curving, with 8 sharp, slightly inclined, loosely arranged, proximally diminishing spines more or less obscured by fine setae; extensor margin with plumose setae on median portion.

REMARKS — The new species strongly resembles U. maori Borradaile, 1916 in  nearly all aspects. As is suggested by the specific name, U. inermis  is readily differentiated from U. maori  by lack of a subterminal spine on the ventromesial margin of the P 1 ischium. The combination of the following characters links the species to U. anacaena Baba & Lin 2009  and U. granulipes  n. sp.: the carapace bearing a prominent anterolateral spine, the P 1 merus and carpus granulose, Mxp3 spineless on the merus and carpus, and the P 2-4 dactyli bearing proximally diminishing triangular spines. The most obvious differences that distinguish U. anacaena  from the new species are: the antennal article 2 that bears a distinct distolateral spine, the carapace that is granulose on the entire surface, and the rostrum that is much less than half as broad as the the carapace measured along the posterior margin. Uroptychus inermis  is distinguished from U. granulipes  by the P 1 ischium that is unarmed instead of bearing a pronounced subterminal spine on the ventromesial margin, the antennal article 4 is unarmed instead of bearing a small but distinct spine, and the anterolateral spine of the carapace is situated distinctly posterior to instead of directly lateral to the lateral orbital spine.