Uroptychus buantennatus, 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 : 131-134

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Uroptychus buantennatus

n. sp.

Uroptychus buantennatus n. sp.

Figures 50 View FIGURE 50 , 51 View FIGURE 51

TYPE MATERIAL — Holotype: New Caledonia, Hunter and Matthew Islands . VOLSMAR Stn DW 20, 22°21’S, 171°24’E, 460-500 m, 03.VI.1989, with corals of Antipatharia (Hexacorallia), ov. ♀ 3.0 mm ( MNHN-IU-2014-16354 ) GoogleMaps . Paratypes: same station as for the holotype, same host, 1 ♂ 2.5 mm (MNHN-IU-2014-16355). New Caledonia, Norfolk Ridge. NORFOLK 1 Stn DW1704, 23°45’S, 168°16’E, 400-420 m, 25.VI.2001, 1 ♂ 2.5 mm (MNHN-IU-2014-16356).

ETYMOLOGY„ From the Latin bu (prefix meaning large, huge) plus antenna plus tus (suffix denoting possession), referring to the relatively large size of the antennal peduncle displayed by the species.

DISTRIBUTION„ Hunter-Matthew Islands and Norfolk Ridge; 400- 500 m.

DESCRIPTION — Small species. Carapace: 1.3 × broader than long; greatest breadth 1.8 × distance between anterolateral spines. Dorsal surface smooth and unarmed, slightly convex from anterior to posterior, without distinct depression in profile. Lateral margins armed with 5 spines, divergent posterolaterally toward last spine and convergent behind it; first anterolateral, medium-sized, more or less close to and barely overreaching lateral orbital spine; second much smaller than first (absent on left side on male paratype), distinctly anterior to midpoint between first and third, third largest, situated at midlength; fourth somewhat smaller than third, about at point one-third from posterior end; last very small or obsolete. Rostrum nearly horizontal, narrow triangular, with interior angle of 15-19°, overreaching distal end of P 1 merus, length subequal to postorbital carapace length, breadth less than half carapace breadth measured at posterior carapace margin; dorsal surface concave; lateral margin entire. Lateral orbital spine subequal to or slightly smaller than anterolateral spine. Pterygostomian flap smooth on surface, anteriorly angular, ending in distinct spine.

Sternum: Excavated sternum subtriangular on anterior margin, surface with ridge in midline. Sternal plastron 1.4 × broader than long, lateral extremities posteriorly divergent. Sternite 3 moderately depressed, anterior margin of broad V-shape (medially rounded in male paratype, MNHN-IU-2014-16356), anterolaterally sharply angular. Sternite 4 with anterolateral margin convex, bearing a few small blunt spines anteriorly, posterolateral margin two-thirds length of anterolateral margin. Anterolateral margin of sternite 5 anteriorly convex, about as long as posterolateral margin of sternite 4.

Abdomen: Smooth and glabrous. Somite 1 smooth on surface, feebly convex from anterior to posterior. Somite 2 tergite 2.5-2.8 × broader than long; pleuron anterolaterally blunt angular, lateral margins strongly concave and posteriorly produced to angular point. Pleuron of somite 3 moderately angular on lateral end. Telson about half as long as broad; posterior plate feebly concave on posterior margin, length 1.5 × that of anterior plate.

Eye: 1.7-1.8 × longer than broad, not reaching midlength of rostrum; lateral and mesial margins subparallel. Cornea not dilated, length about half that of remaining eyestalk.

Antennule and antenna: Ultimate article of antennular peduncle 3.3-3.5 × longer than high. Antennal peduncle broad relative to length, article 5 in particular, overreaching midlength of rostrum. Article 2 with sharp distolateral spine. Antennal scale slender, slightly narrower than article 4, reaching distal end of article 5. Article 4 with small distomesial spine. Article 5 broadened distally, with very strong distomesial spine (mesially with small accompanying spine in holotype); greatest breadth 1.5 × that of antennal scale, 1.5 × height of antennular ultimate article; length 1.3-1.4 × that of article 4. Flagellum consisting of 7-8 segments, slightly overreaching distal ends of both rostrum and P 1 merus.

Mxp: Mxp1 with bases more or less close to each other but distinctly separated. Mxp3 barely setose on ischium and merus. Basis with a few obsolescent denticles on mesial ridge. Ischium relatively thick, with about 20 denticles on crista dentata, flexor margin not rounded distally. Merus 1.8 × longer than ischium, flexor margin not cristate but rounded, with very small spine at distal quarter of length; distolateral spine small. Carpus with small distolateral spine.

P 1: 4.5 × longer than carapace, massive, subcylindrical except for palm and fingers, sparsely bearing short, fine setae along lateral and mesial margins. Ischium dorsally with short blunt spine, ventromesially with no subterminal spine

(additional small spine at point proximal quarter in holotype); row of very small ventral spines along mesial margin. Merus as long as carapace, armed with 4 terminal spines (2 dorsal and 1 dorsolateral much pronounced, ventromesial smaller and blunt, no ventrolateral) plus strong mesial spine somewhat distal to midlength (2 additional small spines proximal to 2 dorsal terminal on left side in holotype); length subequal to that of carapace. Carpus 1.3 × longer than merus, with 2 rows of dorsal spines. Palm 2.5 × longer than broad, 1.3 × longer than carpus, 2.1-2.5 × longer than movable finger; dorsal surface with several small spines on proximal portion. Fingers broad relative to length, strongly incurved distally, crossing when closed, not gaping; fixed finger having opposable margin with dorsoventrally depressed, low triangular process distal to opposite proximal process of movable finger; movable finger slightly falling short of distal end of fixed finger, length half that of palm.

P 2-4: Sparsely setose, meri successively shorter posteriorly ( P 3 merus 0.91-0.95 × length of P 2 merus, P 4 merus 0.80- 0.87 × length of P 3 merus), equally broad on P 2 and P 3, slightly narrower (0.9) on P 4 than on P 3; length-breadth ratio, 3.5-3.9 on P 2, 3.3-3.6 on P 3, 3.0-3.3 on P 4; dorsal margin with 4-5 proximally diminishing spines on P 2 and P 3, 0 or 2 on P 4; no spine on ventrolateral margin; P 2 merus 0.8 × as long as carapace, about as long as or slightly longer than P 2 propodus; P 3 merus 0.8-0.9 × length of P 3 propodus; P 4 merus 0.9 × length of P 4 propodus. P 3 carpus subequal to or slightly longer than P 4 carpus, 0.8-0.9 × length of P 2 carpus, carpus-propodus length ratio, 0.54-56 on P 2, 0.43-0.45 on P 3, 0.42 on P 4; extensor margin with row of small spines, 6 on P 2, 3 on P 3 and P 4 (spines obsolescent on P 3 and P 4 in paratype of MNHN-IU-2014-16355). Propodi subequal; flexor margin somewhat convex around distal quarter, ending in pair of movable spines preceded by 5 ( P 2) or 3-4 ( P 3, P 4) elongate slender spines at least on distal half. Dactyli somewhat curved, longer on P 3 and P 4 than on P 2; slightly longer than carpi on P 2, as long as or slightly longer on P 3, subequal to or slightly shorter on P 4; flexor margin with 7 or 8 loosely arranged spines, ultimate slender, remaining spines subtriangular, moderately inclined, gradually diminishing toward base of article, penultimate much broader, twice as broad as antepenultimate on P 2, less than so on P 3 and P 4.

Eggs. Eggs carried 4 in number; size, 1.0 mm × 1.1 mm.

REMARKS — The combination of the following characters easily distinguishes the new species from the other members of the genus: the long rostrum is subequal to the length of carapace, and the relatively stout antennal peduncle has article 5 distally noticeably broadened with a strong terminal spine, and the massive P 1. The antennal article 5 in the new species is broader than the height of antennular ultimate article as in U. angustus n. sp. (see above) but U. buantennatus is readily distinguished from that species by having no spine on the carapace dorsal surface, by having the sternite 3 anterior margin V-shaped without median notch, and by having P 1-4 broader relative to length, with P 1 ischium unarmed on the ventromesial margin.

The species is somewhat similar to U. triangularis Miyake & Baba, 1967 in the spination of the carapace and P 2-4 meri. In addition to the above-mentioned differences, U. buantennatus is distinguished from that species by the P 2-4 carpi bearing distinct spines (rarely obsolescent on P 3-4) instead of being unarmed on the extensor margin; and the anterior margin of sternite 3 is V-shaped instead of semicircular.