Uroptychus disangulatus, 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 : 178-181

Uroptychus disangulatus n. sp.

Figures 76 , 77

TYPE MATERIAL — Holotype: French Polynesia, Austral Islands . BENTHAUS Stn DW 1898, 27°34.3’S, 144°26.6’W, 580- 820 m, 8.XI.2002, ov. ♀ 8.0 mm ( MNHN-IU-2014-16390 ) . Paratypes: French Polynesia, Austral Islands. Station data as for the holotype, 1 ♂ 4.7 mm (MNHN-IU-2014-16391) . – Stn DW 2001, 22°26.6’S, 151°20.1’W, 200-550 m, with Chrysogorgiidae gen. sp. ( Calcaxonia ), 23.XI.2002, 1 ♂ 8.1 mm (MNHN-IU-2014-16392). New Caledonia, Hunter and Matthew Islands . VOLSMAR Stn DW 05, 22°26’S, 171°46’E, 620-700 m, 01.VI.1989, 1 ♀ 7.8 mm (MNHN-IU-2014-16393). New Caledonia, Norfolk Ridge. NORFOLK 2 Stn DW 2027, 23°26.34’S, 167°51.38’E, 465-650 m, 21.X.2003, 2 ♂ 7.1, 8.6 mm, 1 ov. ♀ 9.9 mm (MNHN-IU-2014-16394) .

ETYMOLOGY„ From the Latin dis (without) plus angulatus (having angles), alluding to the absence of lateral orbit spine, a character to distinguish the species from U. brevisquamatus .

DISTRIBUTION„ Hunter-Matthew, Norfolk Ridge and French Polynesia; in 200- 820 m.

DESCRIPTION„ Medium-sized species. Carapace: As long as broad; greatest breadth 1.7 × distance between anterolateral spines. Dorsal surface smooth or somewhat granulose, moderately convex from anterior to posterior, with depression between gastric and cardiac regions; epigastric region with pair of denticulate ridges. Lateral margins convex posteriorly, with somewhat elevated, short granulate ridge at anterior end of branchial region, and ridged along posterior third or posterior half; anterolateral spine relatively large, overreaching lateral limit of orbit without spine. Rostrum anteriorly ending in blunt or rounded margin, with interior angle of 22-27°, somewhat overreaching eyes; length at most one-third postorbital carapace length, breadth less than half carapace breadth measured at posterior carapace margin; dorsal surface flattish. Lateral limit of orbit rounded, not angular, lacking spine. Pterygostomian flap anteriorly roundish, ending in small spine; surface somewhat granulose.

Sternum: Excavated sternum with low ridge in midline or weak tubercle-like process in center, anterior margin sharp or blunt triangular. Sternal plastron moderately broadened posteriorly, slightly shorter than broad. Sternite 3 depressed well, anterior margin deeply excavated, with pair of small submedian spines separated by narrow or small V-shaped median notch; lateral margin with distinct spine at midlength. Sternite 4 with anterolateral margin convex and anteriorly ending in roundish terminus; posterolateral margin relatively long, more than half length of anterolateral margin. Anterolateral margin of sternite 5 convex well, about as long as posterolateral margin of sternite 4.

Abdomen: Smooth, barely setose. Somite 1 strongly convex from anterior to posterior. Somite 2 tergite 2.3-2.5 × broader than long; lateral margin strongly divergent, posterolateral corner bluntly angular. Pleura of sternites 3 and 4 posterolaterally angular. Telson half as long as broad; posterior plate emarginate on posterior margin, length 1.3-1.6 × that of anterior plate.

Eye: Long relative to breadth, about twice as long as broad, reaching distal quarter of rostrum; mesial margin concave proximal to cornea. Cornea slightly more than half length of remaining eyestalk.

Antennule and antenna: Ultimate article of antennular peduncle 2.1-2.5 × longer than high. Antennal peduncle slightly overreaching cornea. Article 2 produced to short, stout spine on distal lateral margin. Antennal scale relatively broad (1.7-2.0 × as broad as article 4), roundly truncate or ending in blunt tip, varying from overreaching to barely reaching midlength of antennal article 5, not reaching its distal end. Distal 2 articles unarmed; article 5 2.0 × longer than article 4, breadth slightly less than half height of ultimate antennular article. Flagellum consisting of 13-17 segments, reaching or barely reaching distal end of P1 merus.

Mxp: Mxp1 with bases close to each other, slightly separated or nearly contiguous. Mxp3 unarmed on merus and carpus. Basis with 3-4 denticles on mesial ridge. Ischium short relative to merus, flexor margin not rounded distally, crista dentata with 22-26 denticles. Merus 2.4 × longer than ischium, thick mesio-laterally, with rounded ridge along flexor margin. No spine on carpus.

P1: Relatively massive, 4.0-4.4 × longer than carapace, barely setose except for fingers, bearing tubercles on ventral surface of ischium, merus and carpus (smooth in smallest male). Ischium dorsally with basally broad, depressed, relatively short distal spine, ventrally with rudimentary subterminal spine on mesial margin. Merus subequal to or slightly longer than carapace, ventrally weakly granulose bearing distomesial and distolateral spines occasionally obsolescent. Carpus 1.0-1.2 × longer than merus. Palm 2.2-2.6 × longer than broad, as long as carpus. Fingers distally incurved, crossing when closed, slightly gaping in males, not gaping in females; opposable margin of movable finger with low proximal process (bidentate in males); that of fixed finger sinuous in proximal third in males, nearly straight in females; movable finger 0.6 × as long as palm.

P2-4: Unarmed on meri and carpi, distal 2 articles with sparse long setae. Meri moderately compressed mesio-laterally, distally narrowed, successively shorter posteriorly (P3 merus‰.9 × length of P2 merus, P4 merus‰.8-0.9 × length of P3 merus), subequal in breadth on P2-4; length-breadth ratio, 4.8-5.3 on P2, 4.2-4.7 on P3, 3.4-3.8 on P4; P2 merus 0.9-1.0 × length of carapace, 1.3-1.4 × length of P2 propodus; P3 merus 1.2 × length of P3 propodus; P4 merus 0.8-0.9 × length of P4 propodus. Carpi subequal or successively shorter posteriorly (P3 carpus 0.9-1.0 × length of P2 carpus, P4 carpus 0.9 × length of P3 carpus), carpus-propodus length ratio, 0.5-0.6 on P2, 0.5 on P3, 0.4-0.5 on P4. Propodi subequal on P2-4 or somewhat longer on P4 than on P2 and P3; flexor margin nearly straight, terminating in pair of spines preceded by 6-9 spines on P2, 6-8 on P3, 4-6 on P4. Dactyli slender relative to propodi, subequal, about one-third (max. 0.4) length of propodi; dactylus-carpus length ratio, 0.6-0.7 on P2 and P3, 0.7-0.8 on P4; flexor margin with 11 moderately loosely arranged spines, ultimate longest, penultimate and antepenultimate subequal and shorter than ultimate, remaining spines small, blunt and oriented parallel to flexor margin, all obscured by setae.

Eggs. Number of eggs carried, 4-13; size, 1.48 mm × 1.65 mm - 1.55 mm × 1.68 mm; 4 ova carried by the specimen from Norfolk 2, Stn DW2027 nearly ready to hatch.

REMARKS — The ocular peduncles in the specimens from the Norfolk Ridge (MNHN-IU-2014-16394) are much more slender than in the other specimens, and the carapace is finely granulose in the female (9.9 mm) and the smaller male (7.1 mm), faintly so in the larger male (8.6 mm).

This species has a carapace bearing an anterolateral spine only on the lateral margin and the P2-4 dactyli bearing small spines oriented parallel to the flexor margin, characters also possessed by U. australis ( Henderson, 1885) and U. brevirostris Van Dam, 1933 . Uroptychus disangulatus is distinguished from these species by the lateral limit of the orbit, which is rounded and unarmed instead of produced to a distinct spine; the antennal scale, which is broader and distally blunt or rounded instead of distally tapering; and the flexor marginal spines of the P2-4 dactyli, which are much shorter. In addition, U. disangulatus differs from U. australis in the P4 merus-P3 merus length ratio which is 0.8-0.9 instead of 0.6, and in having the anterolateral spine located very slightly posterior to the lateral orbital angle instead of being more posterior. Uroptychus brevirostris has broader P2-4 meri, i.e., the length-breadth ratio on P2 merus being 3.5-3.6 instead of more than 4.8 as in U. australis and U. disangulatus .

The new species also strongly resembles U. brevisquamatus Baba, 1988 (see above) and U. webberi Schnabel, 2009 from the Kermadec Ridge, in the shape of the carapace, sternal plastron, and in the spination of the P2-4 dactyli. In U. brevisquamatus , the lateral orbital spine is distinct; the P1 ischium bears a distinct subterminal spine rather than being unarmed on the ventromesial margin; and the terminal of the flexor marginal spines of P2-4 propodi is single, not paired as in the present new species. Uroptychus disangulatus differs from U. webberi in the following particulars: the lateral limit of the orbit is rounded instead of ending in a spine; the carapace lateral margins are convex instead of subparallel along the branchial region; the Mxp3 ischium bears 22-26 instead of 12 denticles on the crista dentata; and the P1 ischium bears a rudimentary instead of small but distinct subterminal spine on the ventromesial margin.

Figures

FIGURE 76 Uroptychus disangulatus n. sp.,holotype, ovigerous female 8.0 mm (MNHN-IU-2014-16390).A, carapace and anterior part of abdomen,proximal part of P1 included, dorsal. B, same,lateral.C, sternal plastron, with excavated sternum and basal parts of Mxp1. D, telson. E, left antenna, ventral.F, right Mxp3, ventral. G, same, lateral.H, right P1, proximal part, ventral.I, same, proximal part omitted, dorsal.Scale bars: A, B,H, I, 5 mm; C-G,1 mm.

FIGURE 77 Uroptychus disangulatus n. sp., holotype, ovigerous female 8.0 mm (MNHN-IU-2014-16390).A, right P2, lateral. B, same, distal part, setae omitted, lateral.C, left P3,setae omitted,lateral. D, left P4,lateral. Scale bars:1 mm.