Uroptychus thermalis Baba & de Saint Laurent, 1992

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 : 518-522

Uroptychus thermalis Baba & de Saint Laurent, 1992

Figures 261-263

Uroptychus thermalis Baba & de Saint Laurent, 1992: 324 , fig. 2. — Chevaldonné & Olu 1996: 293. — Ahyong & Poore 2004 a: 77, fig. 24. — Baba 2005: 231.

TYPE MATERIAL — Holotype: North Fiji Basin, 16°59.50’S, 173 °55.47’W, hydrothermal vent, 2000 m, male ( MNHN-Ga 2351 ). [examined].

MATERIAL EXAMINED — New Caledonia. BIOCAL Stn CP72, 22°10’S, 167°33’E, 2100-2110 m, 4.IX.1985, 1 ♀ 8.1 mm (MNHN-IU-2014-16988) .

DISTRIBUTION„ North Fiji Basin (active thermal vent site), Queensland, and now New Caledonia; 1497-2110 m.

DIAGNOSIS„ Medium-sized species. Carapace slightly longer than broad; greatest breadth 1.6 × distance between anterolateral spines. Dorsal surface with elevated, granulate, short ridges; gastric and cardiac regions distinctly bordered by deep groove, and both well inflated; anterolateral spine directed anterolaterally, overreaching angular lateral limit of orbit, followed by no spine but a row of short granulate ridges along branchial margin. Rostrum narrow triangular, with interior angle of 22-26°; breadth half length of posterior carapace margin; dorsal surface smooth, slightly convex from side to side. Pterygostomian flap with roundish anterior margin bearing small spine. Excavated sternum anteriorly convex with small spine, surface with small central spine; sternal plastron 1.2 × broader than long; lateral extremities divergent posteriorly; sternite 3 depressed, anterior margin moderately concave, with pair of small submedian spines; sternite 4 with strong spine about at midlength of anterolateral margin, posterolateral margin as long as anterolateral margin; sternite 5 with anterolateral margin straightly divergent posteriorly, slightly more than half as long as posterolateral margin of sternite 4. Abdomen smooth and glabrous, somite 1 strongly convex from anterior to posterior; somite 2 tergite 2.0 × broader than long; pleuron having lateral margin concavely strongly divergent posteriorly, ending in blunt tip; pleuron of somite 3 blunt on lateral terminus. Telson three-fifths as long as broad; posterior plate subsemicircular, posteriorly rounded, length 1.7 × that of anterior plate. Eyes short relative to breadth; cornea inflated, as long as remaining eyestalk. Ultimate article of antennular peduncle 2.5 × longer than high. Antennal peduncle slender, overreaching cornea; article 2 with small lateral spine; antennal scale slightly overreaching article 4; distal 2 articles unarmed, article 5 twice as long as article 4, breadth less than half height of ultimate article of antennule; flagellum of 10 or 11 segments far falling short of distal end of P1 merus. Mxp1 with bases close to each other. Mxp3 slender and spineless; coxa with strong ventral spine; basis with 1 denticle on distal part of mesial ridge; ischium having flexor margin not rounded distally, crista dentata with obsolescent denticles; merus 2.8 × longer than ischium, relatively thick mesio-laterally; carpus longer than ischium. P1 slender; ischium with small dorsal process, ventrally unarmed; merus with 2 prominent distodorsal spines, length 1.4 × that of carapace; carpus 1.5 × longer than merus, with 1 distodorsal and 1 lateral distoventral spine; palm 0.8 × length of carpus; fingers spooned on prehensile face, not crossing distally when closed; movable finger 0.6 × as long as palm; fixed finger with median process opposite to between 2 proximal processes of movable finger. P2-4 slender, subcylindrical on meri and carpi, sparsely setose on distal articles; meri subequally broad on P2-4, unarmed; P2 merus slightly longer than carapace, 1.7 × longer than P2 propodus; P3 merus 0.9 × length of P2 merus; P4 merus 0.9 × length of P3 merus, slightly longer than P4 propodus; carpi long, subequal in length on P2 and P3, slightly shorter on P4 than on P2 and P3, carpus-propodus length ratio, 1.0 on P2, 0.8 on P3 and P4; propodi broadened medially; flexor margin with slender movable spines distal to midlength, distalmost single, slightly proximal to juncture with dactylus, distantly separated from proximal group of 4-5 spines; dactyli strongly curving, 0.4 × as long as propodi on P2-4, and 0.4 × as long as carpi on P2 and P3, 0.5 × on P5, flexor margin with terminal and subterminal spines of good size (subterminal spine absent in this specimen), both remotely separated from proximal group of 6 very small obliquely directed spines.

REMARKS„ No clear differences were found in the relative lengths of articles of P2-4 between the type and the present material. Apparently this female specimen is identical with the male reported by Ahyong & Poore (2004) from a non-vent site in Queensland, sharing the presence of a strong lateral spine on sternite 4, two distodorsal spines on the P1 merus and one distodorsal spine on the P1 carpus. In the type material, the lateral spine of sternite 4 is very small, the P1 merus bears one instead of two spines, and the P1 carpus has no distodorsal spine. Ahyong & Poore (2004) considered these differences as age-related variations, but the present specimen is about as large as in the type material. The crista dentata of the Mxp3 ischium in this specimen bears denticles more obsolescent than in the type. Given that the type material was taken from the active thermal vent-site, the material from Queensland and New Caledonia may be referable to a different species. However, this is provisionally placed in U. thermalis , pending a discovery of additional material from the type locality and molecular analyses.

The spination of the P2 dactylus is illustrated here for the BIOCAL specimen; the small spines on the proximal portion are also discernible under high magnification in the type ( Figure 263E ). Dactylar and propodal spination of the P2-4 are similar between U. thermalis and U. sternospinosus Tirmizi, 1964 , as also are the slender pereopods, short antennal scales, and the shape of the sternal plastron. In U. sternospinosus , however, the P2-4 carpi are consistently longer than the propodi, and the carapace bears a distinct longitudinal carina in midline and a pair of strong gastric spines, the characters confirmed by examination of the type material (BMNH 1966.2.3.21-22).

Figures

FIGURE 261 Uroptychus thermalis Baba & de Saint Laurent,1992,female 8.1 mm (MNHN-IU-2014-16988).A, carapace,dorsal.B, same,anterior part of abdomen included,lateral.C, sternal plastron,with excavated sternum and basal parts of Mxp1.D, telson.E, right antenna, ventral.F, right Mxp3,ventral.G, same,lateral.Scale bars:1 mm.

FIGURE 262 Uroptychus thermalis Baba & de Saint Laurent, 1992, female 8.1 mm (MNHN-IU-2014-16988). A, right P1, dorsal. B, right P2, lateral. C,right P3,setae omitted,lateral.D,same,distal part,lateral.E,right P4,lateral.F,same,distal part,lateral.Scale bars:A,5 mm;B-F,1 mm.

FIGURE 263 Uroptychus thermalis Baba & de Saint Laurent,1992,male holotype 8.4 mm (MNHN-IU-2014-12825 [=MNHN-Ga 2351]).A, right P1, setae omitted, dorsal. B, sternal plastron, with excavated sternum and basal parts of Mxp1. C, right Mxp3, setae omitted, ventral.D, right P2, setae omitted, lateral. E, same,distal part, lateral.F, right P3,lateral.G, right P4, lateral.Scale bars: 1 mm.