Uroptychus depressus, 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 : 170-174

Uroptychus depressus n. sp.

Figures 71 , 72

TYPE MATERIAL — Holotype: New Caledonia, Norfolk Ridge. CHALCAL 2 Stn CP22, 24°40’S, 168°39’E, 650-750 m, 29.X.1986, ♀ 4.5 mm (MNHN-IU-2012-691) . Paratypes: Wallis and Futuna Islands. MUSORSTOM 7 Stn DW578, 13°08’S, 176°16’W, 640-730 m, 22.V.1992, 1 ♂ 3.6 mm (MNHN-IU-2014-16387) . Tonga. BORDAU 2 Stn DW1553, 20°42’S, 174°54’W, 650-676 m, 6.VI.2000, 1 ♂ 3.0 mm (MNHN-IU-2014-16388) .

ETYMOLOGY„ From the Latin depressus (= depressed), alluding to the depressed rostral surface clearly bordering the gastric and rostral regions.

DISTRIBUTION„ Wallis and Futuna Islands, Tonga and Norfolk Ridge; 640- 750 m.

DESCRIPTION — Small species. Carapace: Slightly broader than long (0.9 × as long as broad), greatest breadth 1.7 × distance between anterolateral spines. Dorsal surface glabrous, nearly horizontal or weakly convex from anterior to posterior, with feeble depression between gastric and cardiac regions; epigastric region with transverse row of small spines (median spine flanked by 2 denticles placed side by side), preceded by depressed rostrum. Lateral margin posteriorly divergent along hepatic region, slightly convexly divergent along branchial region; anterolateral spine well developed, slightly overreaching lateral orbital spine; branchial margin with 5-7 posteriorly diminishing spines, anteriormost as large as or slightly larger than anterolateral spine, last spine followed by distinct ridge; small spine between and ventral to level of anterolateral and anteriormost branchial marginal spines. Small spine mesial to anteriormost branchial spine. Rostrum narrow subtriangular, with interior angle of 18°, nearly horizontal, dorsal surface excavated; lateral margin unarmed or with 2 tiny denticle-like spines on distal portion; length half that of remaining carapace. Lateral orbital spine small, situated slightly anterior to level of anterolateral spine. Pterygostomian flap smooth or with a few small spines on anterior surface, anteriorly more or less angular, ending in distinct spine.

Sternum: Excavated sternum anteriorly triangular, surface with weak ridge in midline. Sternal plastron 0.9-1.0 × as long as broad, lateral extremities somewhat divergent posteriorly. Sternite 3 moderately depressed, anterior margin concave, laterally sharp angular, with narrow U-shaped median sinus flanked by small or obsolescent spine; lateral margin with small blunt spine. Sternite 4 with anterolateral margin straightly divergent posteriorly, anteriorly angular or produced; posterolateral margin longer than anterolateral margin.

Abdomen: Smooth and glabrous. Somite 1 convex from anterior to posterior, forming rounded transverse ridge. Somite 2 tergite 2.4 × broader than long; pleural lateral margin feebly convex, slightly divergent posteriorly, anterior and posterior ends both rounded. Pleural lateral margin of somite 3 blunt on posterior end. Telson slightly less than half as long as broad; posterior plate feebly concave on posterior margin, length 1.3-1.4 × that of anterior plate, greatest breadth not more than distance between left and right constrictions of telson.

Eye: Short relative to breadth (length 1.4 × breath), barely reaching or slightly overreaching midlength of rostrum, narrowed proximally and distally, mesial and lateral margins convex, cornea more than half length of remaining eyestalk.

Antennule and antenna: Ultimate article of antennule 3.0-3.1 × longer than high. Antennal peduncle overreaching eye, falling short of apex of rostrum. Article 2 of antennal peduncle with distinct lateral spine. Antennal scale overreaching article 5, reaching proximal first or second segment of flagellum, breadth more than twice that of article 5. Article 4 with short distomesial spine. Article 5 unarmed, length 1.3-1.4 × that of article 4, breadth half height of antennular ultimate article. Flagellum consisting of 9-11 segments, falling short of end of P1 merus, length less than that of rostrum.

Mxp: Mxp1 with bases broadly separated. Mxp3 basis without denticles on mesial ridge. Ischium with tuft of long setae lateral to rounded distal end of flexor margin, no distinct denticles on crista dentata. Merus 2.1 × longer than ischium, flexor margin somewhat roundly ridged, bearing small blunt spine distal to midlength; distolateral spine on each of merus and carpus.

P1: Slender, smooth and polished, sparsely setose except for fingers; length 5.5-6.0 × that of carapace. Ischium with distinct dorsal spine, ventromesially with strong subterminal spine followed by 2 distal and 2 much smaller proximal spines. Merus with 3 tiny dorsal spines on distal margin, ventrally with small spines not numerous but moderate in number, ventrolaterally with small distal spine, ventromesially with 3 well-developed spines, distal spine terminal and strongest, median spine at point one-third from proximal end; length 1.2 × that of carapace. Carpus as long as or slightly shorter than palm, with 2 small ventral (ventomesial and ventrolateral) and 2 dorsal (on distal margin) spines. Palm 3.7 × (males) or 5.9 × (female) longer than broad, 3 × longer than fingers. Fingers gaping in proximal half, feebly crossing at tip, not spooned; opposable margin of movable finger with prominent blunt proximal process of subtriangular shape fitting to opposing concavity of fixed finger when closed.

P2-4: Relatively thick mesio-laterally, sparsely setose on meri and carpi, moderately so on distal part of propodi and entire dactyli. Meri successively shorter posteriorly (P3 merus 0.9 × length of P2 merus, P4 merus 0.8 × length of P3 merus), subequally broad on P2-4; length-breadth ratio, 3.2-3.8 on P2, 2.8-3.1 on P3, 2.4-2.5 on P4; dorsal margin not crested, rounded; ventrolateral margin ending in small spine. P2 merus 0.7 × length of carapace, subequal to length of P2 propodus; P3 merus 0.9 × length of P3 propodus; P4 merus 0.7-0.8 × length of P4 propodus. Carpi subequal, length less than half that of propodus (0.4 on P2 and P3, 0.3 on P4). Propodi subequal on P2 and P3, longer on P4; flexor margin straight, ending in pair of slender movable spines preceded by row of 4 or 5 (P2 and P3), 3 or 4 (P4) single movable spines at most on distal half. Dactyli successively longer posteriorly, length 1.4 × that of carpus on P2, 1.7 × on P3, 1.9 × on P4, 0.5 × length of propodus on P2, 0.6 × on P3 and P4; flexor margin slightly curving, with row of 18 or 19 obliquely directed spines obscured by setae, ultimate slender, penultimate prominent, slightly more than 2 × broader than antepenultimate, remaining proximal spines including antepenultimate close to each other, subequal to ultimate in breadth; antepenultimate spine 2.7-2.9 × longer than broad.

REMARKS — This new species is very similar to U. levicrustus Baba, 1988 from the Moluccas and U. kareenae n. sp. (see below) in having a row of branchial marginal spines, in having the anterior margin of sternite 3 with a median sinus separated by obsolescent submedian spines, and in the spination of P2-4. Uroptychus depressus is distinguished from U. levicrustus by having the epigastric region anteriorly preceded by the depressed rostrum, instead of being gently sloping down on to the rostrum ( Figure 73 ); the eyes are medially swollen and narrowed distally and proximally, instead of having subparallel lateral and mesial margins; the antennal scale overreaches the first segment of the antennal flagellum, instead of barely reaching the distal end of antennal article 5; and the ultimate spines of the P2-4 dactyli are more slender than instead of as slender as the antepenultimae. The relationships with U. kareenae are discussed under the remarks of that species (see below).

Figures

FIGURE 71 Uroptychus depressus n. sp., holotype, female 4.5 mm (MNHN-IU-2012-691). A, Carapace and anterior part of abdomen, dorsal. B, same, lateral. C, sternal plastron,with excavated sternum and basal parts of Mxp1. D, telson.E, left antenna,ventral.F, right Mxp3,setae omitted,ventral.G, same, lateral. Scale bars:1 mm.

FIGURE 72 Uroptychusdepressus n.sp.,holotype,female 4.5 mm (MNHN-IU-2012-691).A, left P1,proximal part,ventral.B,same,dorsal.C, same,mesial.D,same, proximal part omitted, dorsal. E, same, fingers, ventral. F, right P2, lateral. G, same, distal part, setae omitted, lateral. H, right P3, setae omitted, lateral.I, same,distal part,setae omitted,lateral. J, right P4, setae omitted, lateral.K, same,distal part, setae omitted,lateral.Scale bars:1 mm.

FIGURE 73 Uroptychus levicrustus Baba, 1988,holotype,ovigerous female 4.7 mm (USNM 150309). A, carapace and anterior part of abdomen, lateral. B, right Mxp3,ventral.C, P1,proximal articles,ventral.D, right P2,lateral.E, same,distal part,setae omitted,lateral.F, right P3,setae omitted, lateral.G, right P4, setae omitted,lateral.H, same, distal part, lateral. Scale bars: 1 mm.