Uroptychus inaequalis, 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 212), pp. 1-612 : 236-239

Uroptychus inaequalis n. sp.

Figures 107 , 108

Uroptychus pilosus — Ahyong & Poore 2004: 71 , fig. 21 (not U. pilosus Baba, 1981 ).

TYPE MATERIAL — Holotype: New Caledonia, Loyalty Islands. CALSUB PL07, 20°48’S, 167°05’E, 970- 489 m, 25.II.1989, ♀ 5.1 mm ( MNHN-IU-2011-5948 ) . Paratypes: Solomon Islands. SALOMON 2 Stn CP2197, 08°24’S, 159°23’E, 897- 1057 m, 24.X.2004, 1 ♂ 4.4 mm (MNHN-IU-2011-5952) . – Stn CP2273, 8°31.8’S, 157°42.8’E, 732-839 m, 5.XI.2004, 1 sp., sex indet. [female gonopores present, male gonopods distinct], 5.2 mm (MNHN-IU-2011-5949) . – Stn CP2297, 9°08.8’S, 158°16.0’E, 728-777 m, 8.XI.2004, 1 ♂ 4.4 mm, 1 ♀ 4.2 mm (MNHN-IU-2011-5950 & MNHN-IU-2011-5951) .

ETYMOLOGY„ From the Latin inaequalis (unequal), alluding to the two terminal spines of different sizes on the P2-4 dactyli, the character to separate the species from U. pilosus Baba, 1981 .

DISTRIBUTION„ New South Wales, and now Solomon Islands and Loyalty Islands; in 728-1057 m.

SIZE„ Males, 4.4 mm; females, 4.2-5.1 mm.

DESCRIPTION„ Medium-sized species. Carapace: Usually shorter (0.9 ×) than, rarely as long as broad; greatest breadth 1.7 × distance between anterolateral angles. Dorsal surface smooth, slightly convex, with very faint depression between gastric and cardiac regions, sparsely or thickly with short fine setae; gastric region anteriorly abruptly descending to depressed rostrum. Lateral margins convex on branchial region, with small denticles and short setae; anterolateral cor- ner rounded, with a few denticles or small spines (subequal to or smaller than lateral orbital spine). Rostrum straight horizontal, subtriangular with interior angle of 34-40°, distally blunt or roundish with very small denticles, dorsally flattish or slightly concave; length 0.3-0.4 × that of remaining carapace, breadth half carapace breadth measured at posterior carapace margin. Pterygostomian flap anteriorly angular, produced to sharp, anterolaterally directed spine, surface with plumose setae; posterior portion about half as high as anterior portion.

Sternum: Excavated sternum bluntly subtriangular on anterior margin; surface with rounded ridge in midline. Sternal plastron about as long as broad, slightly longer or slightly shorter, with subparallel lateral extremities. Sternite 3 well depressed, anterior margin excavated in broad V-shape, with ovate or V-shaped median notch flanked by small spine. Sternite 4 slightly narrower than sternite 5; anterolateral margin nearly straight or somewhat convex, with or without a few denticles on anterior portion, anteriorly ending in angular terminus; posterolateral margin about as long as anterolateral margin. Anterolateral margin of sternite 5 somewhat convexly divergent posteriorly, distinctly shorter than posterolateral margin of sternite 4.

Abdomen: Somite 1 moderately convex from anterior to posterior. Somite 2 tergite 2.1-2.4 × broader than long; pleuron slightly concave and slightly divergent posteriorly, posterolaterally blunt. Pleuron of somite 3 laterally blunt. Telson about half as long as broad; posterior plate 1.3-1.5 × longer than anterior plate, posterior margin feebly or distinctly emarginate.

Eye: Less than twice (1.6-1.8 x) as long as broad, slightly narrowed distally, slightly overreaching midlength of rostrum. Cornea not dilated, about half as long as remaining eyestalk.

Antennule and antenna: Ultimate article of antennule 3.0-3.3 × longer than high. Antennal peduncle reaching or slightly overreaching rostrum. Article 2 with strong distolateral spine. Antennal scale 1.5 × as broad as article 5, reaching or slightly overreaching article 4; lateral margin occasionally with a few small spines. Distal 2 articles unarmed. Article 5 1.4-1.5 × longer than article 4, breadth‰.4 × height of antennular ultimate article. Flagellum of 11-12 segments not reaching distal end of P1 merus.

Mxp: Mxp1 with bases broadly separated. Mxp3 with plumose setae on lateral surface of merus and carpus. Basis with 1 distal denticle. Ischium having crista dentata with 16-20 denticles much smaller in distal half; flexor margin not rounded distally. Merus 2.3 × longer than ischium, with small distolateral spine and 2-6 small spines distal to midlength of flexor crest. Carpus unarmed.

P1: Slender, subcylindrical, length 4.2-5.3 × (females), 5.6 × (male; missing in another male), 7.3 × (sex indet.) that of carapace, with soft fine setae dense on merus, moderate on fingers, sparse on carpus and palm. Ischium with short broad dorsal spine usually laciniate, rarely not laciniate; unarmed elsewhere. Merus dorsally with denticles and fine setae, length 1.1-1.5 × that of carapace. Carpus 1.3-1.5 × longer than merus. Palm 7.6-7.8 × (male and females), 10.0 × (sex indet.) longer than broad, 1.0-1.1 × length of carpus. Fingers not gaping (slightly gaping in proximal third in sex-indeterminate paratype), distally well incurved, crossing when closed; movable finger quarter to one-fifth length of palm, opposable margin slightly convex or with low prominence proximal to midlength in male, nearly straight in females.

P2-4: Thick mesio-laterally, sparingly with soft setae. Meri successively shorter posteriorly (P3 merus 0.8-0.9 × length of P2 merus, P4 merus 0.8-1.0 × length of P3 merus), equally broad on P2-4; dorsal margin with denticles along proximal half on P2-4; length-breadth ratio, 4.7-5.0 on P2, 4.0-4.2 on P3, 3.3-4.0 on P4; P2 merus 0.8-0.9 × length of carapace, 1.0-1.1 × length of P2 propodus; P3 merus 0.8 × length of P3 propodus; P4 merus 0.7-0.8 × length of P4 propodus. P3 carpus subequal to or very slightly shorter than P2 carpus, P4 carpus 0.9 × length of P3 carpus; length one-third that of propodus on P2-4. Propodi subequal in length on P2-4; flexor margin slightly curving, ending in pair of terminal spines (mesial one often obsolete). Dactyli subequal or slightly shorter on P2 than on P3 and P4, length 1.3-1.4 × that of carpus on P2-4, 0.4-0.5 × length of propodus on P2, 0.4 × on P3 and P4; flexor margin curving, with 2 terminal spines only, proximal much larger than distal.

REMARKS — The present material is identical with the male reported under U. pilosus by Ahyong & Poore (2004) from New South Wales. Ahyong & Poore listed a number of characters that do not fit the original account of U. pilosus and suggested the possibility of either polymorphism or the existence of another related species. Some of the differences they enumerated are actually displayed as intraspecific variations by the present material, but the broad rostrum appears to be consistent: the interior angle of the rostrum is 34-40° in U. pilosus , 23° in the present species. An additional difference worth noting is that the P2-4 dactyli in U. inaequalis are distinctly longer than instead of subequal to the carpi. In addition, the distal of the two terminal spines on the dactyli is much more slender than instead of subequal to the proximal spine.

Figures

FIGURE 107 Uroptychus inaequalis n. sp., holotype, female 5.1 mm (MNHN-IU-2011-5948). A, carapace and anterior part of abdomen, proximal part of right P1 included, dorsal. B, same, lateral.C, sternal plastron with excavated sternum and basal parts of Mxp1. D, telson. E, left antenna, ventral.F, left Mxp3, ventral.G, same, lateral.H, right P1, dorsal. Scale bars:1 mm.

FIGURE 108 Uroptychus inaequalis n. sp.,holotype,female 5.1 mm (MNHN-IU-2011-5948).A, right P2,lateral. B, same,distal part,setae omitted,lateral.C, right P3,lateral.D, right P4,lateral. Scale bars:1 mm.