Uroptychus vulcanus, Baba, 2018

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 30 (212)), pp. 1-612 : 558-561

Uroptychus vulcanus n. sp.

Figures 282 , 283

TYPE MATERIAL — Holotype: New Caledonia, Loyalty Islands. BIOCAL Stn CP109, 22°11’S, 167°16’E, 495-515 m, with gorgonian corals of Primnoidae ( Suborder Calcaxonia ), 9.IX.1985, ov. ♀ 2.0 mm ( MNHN-IU-2013-8534 ).

ETYMOLOGY„ The specific name is derived from the Latin Vulcanus (the god of fire), in the Roman mythology.

DISTRIBUTION„ Loyalty Islands; 495- 515 m.

DESCRIPTION„ Small species. Carapace: Much broader than long (0.6 × as long as broad); greatest breadth 1.7 × distance between anterolateral spines. Dorsal surface moderately convex from anterior to posterior, more so on posterior portion, with small spines scattered on hepatic and branchial regions. Lateral margins with very strong, anterolaterally produced spine at two-fifths from anterior end, bordering posteriorly convergent anterior part and subparallel posterior part; anterior part with well-developed anterolateral spine reaching tip of lateral orbital spine, followed by more than 10 small spines; posterior part well ridged, hanging over pterygostomian flap, bearing numerous very small spines. Rostrum directed slightly dorsally, relatively narrow, sharp triangular, with interior angle of 27°, ending in sharp tip; dorsal surface moderately concave; lateral margin with denticle-like small spines along entire length; length 0.85 × that of remaining carapace, breadth half carapace breadth at posterior carapace margin. Lateral orbital angle produced to well-developed spine situated slightly anterior to position of somewhat larger anterolateral spine. Pterygostomian flap anteriorly angular, produced to distinct spine, surface with spines in 2 rows on anterior portion, one directly below anterior part of linea anomurica, and another on lower part.

Sternum: Excavated sternum nearly transverse on anterior margin, surface smooth. Sternal plastron 1.4 × broader than long, lateral extremities divergent posteriorly. Sternite 3 slightly depressed from level of sternite 4; anterior margin moderately concave with obsolescent median notch, laterally angular with 2 small spines. Sternite 4 having anterolateral margin strongly convex anteriorly, weakly divergent posteriorly; posterolateral margin half as long as anterolateral margin. Anterolateral margin of sternite 5 anteriorly produced to rounded lobe, 1.3 × longer than posterolateral margin of sternite 4.

Abdomen: With sparse short setae. Somite 1 without transverse ridge. Somite 2 tergite 2.6 × broader than long; pleural lateral margins slightly concave, nearly subparallel in dorsal view, posterolaterally rounded. Pleuron of somite 3 with broadly rounded lateral margin. Telson slightly less than half as long as broad; posterior plate four-fifths length of anterior plate, moderately emarginate on posterior margin.

Eye: Relatively short and broad (1.3 × longer than broad), proximally slightly narrowed, slightly overreaching midlength of rostrum; lateral and mesial margins somewhat concave. Cornea slightly dilated, about as long as remaining eyestalk.

Antennule and antenna: Ultimate article of antennular peduncle 3.3 × longer than high. Antennal peduncle overreaching cornea. Article 2 laterally acuminate, without distinct spine. Antennal scale 1.8 × broader than article 5, terminating in midlength of article 5 (left one shorter, possibly regenerated). Distal 2 articles each with distomesial spine, that of article 5 stronger. Article 5 slightly longer than article 4, breadth 0.7 × height of ultimate article of antennule. Flagellum of 5 or 6 segments overreaching apex of rostrum by 2 or 3 segments, not reaching distal end of P 1 merus.

Mxp: Mxp1 with bases broadly separated. Mxp3 basis without denticle on mesial ridge. Ischium having flexor margin not rounded distally, crista dentata with obsolescent denticles. Merus 2.5 × longer than ischium, with strong distolateral spine; flexor margin well ridged along entire length, mesial face concave. Carpus unarmed.

P 1: About 5 × longer than carapace, slender, subcylindrical. Ischium with sharp dorsal spine, unarmed on ventral surface and ventromesial margin. Merus slightly longer than carapace, bearing lateral, dorsal and mesial rows of spines, distal spine of each row prominent; ventral surface unarmed. Carpus 1.6 × longer than merus, with dorsal spines arranged roughly in 2 rows and row of mesial spines. Palm 3.9 × longer than broad, 0.9 × length of carpus, slightly depressed, with a few small spines on proximal part of dorsal surface. Fingers distally slightly crossing when closed, not gaping, sparingly with relatively short setae; movable finger half as long as palm, opposable margin with low proximal process fitting to opposite longitudinal groove on ventral face of fixed finger when closed.

P 2-4: Left P 2 and P 3 missing. P 2-4 relatively short and sparsely setose, more setose on dactyli; P 2 merus 0.8 × length of carapace, as long as P 3 merus, 1.2 × longer than P 2 propodus; P 3 merus 0.7 × length of P 3 propodus; P 4 merus slightly shorter than P 3 merus, 0.7 × length of P 4 propodus; length-breadth ratio, 2.7 on P 2, 2.6 on P 3, 2.5 on P 4; dorsal margin with row of 8-9 spines on P 2 and P 3, 5 obsolescent spines on P 4. Carpi subequal, 0.4 × as long as propodi and 0.7 × as long as dactyli on P 2-4; extensor margin with 2 or 3 spines small on P 2, obsolescent on P 3, absent on P 4. Propodi shorter on P 2 than on P 3 and P 4; flexor margin nearly straight, with pair of slender terminal spines only. Dactyli relatively stout, 1.5 × longer than carpi on P 2-4, 0.50 × as long as propodi on P 2 and P 3, 0.55 × on P 4; flexor margin nearly straight, with 10-11 spines obscured by setae, ultimate spine slender, narrower than antepenultimate, penultimate spine prominent but relatively short, 1.8-2.0 × broader than antepenultimate, remaining spines similar to antepenultimate, obliquely directed and close to one another, diminishing toward proximal end of article.

Eggs. Number of eggs carried, 7; size, 1.10 × 1.30 mm.

REMARKS„ The new species somewhat resembles U. obtusus n. sp. (see above) in the spination of the P 2-4, but they are largely different. In U. vulcanus , the carapace lateral margin bears a strong spine at the anterior two-fifths of length, which spine is absent in U. obtusus ; the lateral orbital spine is well developed, paralleling the larger anterolateral spine, whereas this spine is very small in U. obtusus ; the lateral margin of the rostrum bears denticle-like small spines along the entire length instead of along the distal third; the anterior margin of sternite 3 is deeply concave with a tiny median notch instead of being shallowly concave with a deep median sinus; the posterolateral margin of sternite 4 is distinctly shorter than instead of as long as the anterolateral margin; the anterior margin of the excavated sternum is nearly transverse rather than triangularly produced; and the Mxp3 merus is unarmed instead of bearing two distinct spines on the flexor margin. This species is readily distinguished from other known species of the genus by the combination of the following characters: the rostral lateral margin with numerous denticle-like small spines along the entire length; the carapace is much broader than long, with a prominent, anterolaterally directed spine at the anterior end of each of the subparallel branchial margins; and the lateral orbital spine is well developed but smaller than the anterolateral spine of the carapace.

Figures

FIGURE 282 Uroptychus vulcanus n. sp., holotype, ovigerous female 2.0 mm (MNHN-IU-2013-8534). A, carapace and anterior part of abdomen, proximal part of left P1 included,dorsal.B, same,lateral.C, anterior part of sternal plastron,with excavated sternum and basal parts of Mxp1. D, telson. E, right antenna, ventral.F, right Mxp3, setae omitted,ventral.G, same,lateral.Scale bars:1 mm.

FIGURE 283 Uroptychus vulcanus n. sp., holotype, ovigerous female 2.0 mm (MNHN-IU-2013-8534). A, left P1, proximal part, lateral. B, same, ventral. C, same, proximal part omitted,dorsal.D, right P2,lateral.E, same,distal part,setae omitted,lateral.F,right P3,setae omitted,lateral.G, right P4,setae omitted, lateral. Scale bars:1 mm.