Uroptychus benthaus, 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 : 96-99

Uroptychus benthaus n. sp.

Figures 32 , 33

TYPE MATERIAL — Holotype: French Polynesia, Austral Islands. BENTHAUS Stn DW1873, 29°00’S, 140°15’W, 456- 813 m, with? Chrysogorgiidae gen. sp. ( Calcaxonia ), 4.XI.2002, ♂ 4.6 mm ( MNHN-IU-2014-16327 ) . Paratypes: French Polynesia, Austral Islands. BENTHAUS, collected with holotype, 1 ♂ 6.4 mm, 1 ov. ♀ 6.2 mm (MNHN-IU-2014-16328) . – Stn DW1894, 27°40.1’S, 144°21.5’W, 100 m, 8.XI.2002, 1 ♀ 8.3 mm (MNHN-IU-2014-16329) . – Stn DW1956, 23°18.4’S, 149°27’W, 600-990 m, 18.XI.2002, 1 ♂ 4.9 mm (MNHN-IU-2014-16330) .

ETYMOLOGY„ Named for the cruise Benthaus, by which the type material was collected; used as a noun in apposition.

DISTRIBUTION„ French Polynesia; 100- 813 m.

SIZE„ Males, 4.6-6.4 mm; females, 6.2-8.3 mm; ovigerous females from 6.2 mm.

DESCRIPTION — Medium-sized species. Carapace: 1.1 × longer than broad; greatest breadth 1.5 × distance between anterolateral spines. Dorsal surface smooth, glabrous, moderately convex from anterior to posterior, without distinct depression or groove. Epigastric region with pair of very small spines. Lateral margins convex or convexly divergent posteriorly; anterolateral spine small, situated somewhat posterior to level of but terminating at tip of smaller lateral orbital spine; branchial lateral margin with short protuberant ridge at anterior end, followed by obsolescent granules, weakly ridged along posterior third. Rostrum narrow triangular, with interior angle of 20°, straight horizontal, length half that remaining carapace, breadth subequal to carapace breadth measured at posterior carapace margin; dorsal surface flattish. Pterygostomian flap smooth on surface, anteriorly angular, ending in small sharp spine.

Sternum: Excavated sternum anteriorly produced, ending in spine; surface with small spine in center. Sternal plastron slightly shorter than broad, posteriorly broadened. Sternite 3 well depressed; wide V-shaped anterior margin bearing pair of submedian spines separated by shallow V-shaped notch, laterally angular. Sternite 4 with denticulate, setiferous interrupted transverse ridge; anterolateral margin convex, anteriorly ending in short spine followed by row of denticles, length slightly more than 1.5 × that of posterolateral margin. Anterolateral margin of sternite 5 strongly convex anteriorly and denticulate, about as long as posterolateral margin of sternite 4.

Abdomen: Smooth and glabrous. Somite 1 moderately convex from anterior to posterior. Somite 2 tergite 2.3-2.8 × broader than long; pleuron posterolaterally blunt, lateral margin gently concave and moderately divergent posteriorly. Pleuron of somite 3 bluntly angular laterally. Telson 0.7 × as long as broad; posterior plate sharply emarginate on posterior margin, length twice that of anterior plate.

Eye: Broad relative to length, 1.3-1.4 × longer than broad, proximally slightly narrower, overreaching midlength of rostrum. Cornea slightly broader than and nearly as long as remaining eyestalk.

Antennule and antenna: Ultimate article of antennule 2.1-2.7 × longer than high. Antennal peduncle slightly overreaching cornea. Article 2 with small distolateral spine. Antennal scale slightly falling short of distal end of article 5, breadth 1.2 × that of article 4. Distal 2 articles unarmed. Article 5 2.0-2.2 × length of article 4, breadth less than half height of ultimate antennular article. Flagellum of 12 segments not reaching distal end of P1 merus.

Mxp: Mxp1 with bases close to each other. Mxp3 barely setose on lateral surface. Basis with 1-3 denticles on mesial ridge. Ischium with 10-14 denticles on crista dentata; flexor margin not rounded distally. Merus 2.3 × longer than ischium, moderately thick mesio-laterally, flexor margin unarmed, not sharply ridged. No spine on carpus.

P1: Relatively slender, 4.8-5.5 × longer than carapace; surface smooth and glabrous except for setose fingers. Ischium with short, triangular dorsal spine, ventromesially unarmed. Merus 1.1-1.3 × longer than carapace. Carpus 1.3-1.4 × longer than merus. Palm 4.0-4.1 × (males), 3.7-4.6 × (females) longer than broad, 0.8-0.9 × length of carpus. Fingers gaping in males, not gaping in females, slightly incurved at tip; in females, opposable margin of movable finger with very low proximal process fitting to opposing concavity when closed; in males, opposable margins nearly straight in distal half, gaping in proximal half, bearing process as figured; length of movable finger 0.51-0.54 × that of palm.

P2-4: Moderately compressed, relatively slender, with sparse long setae but meri glabrous. P2 merus slightly shorter than carapace, 1.1 × length of P2 propodus; P3 merus subequal to P2 merus in length and breadth or slightly shorter, subequal to length of P3 propodus; P4 merus 0.7 × length and 0.9 × breadth of P3 merus, 0.8-0.9 × length of P4 propodus; length-breadth ratio, 6.6-6.8 on P2, 6.1-7.0 on P3, 4.8-5.1 on P4; ventrolateral margin with very small terminal spine. Carpi subequal in length on P2 and P3, shorter on P4 (P4 carpus 0.8 × length of P3 carpus); length 0.5-0.6 × that of propodus on P2, 0.5 × on P3 and P4. Propodus longest on P3, shortest on P4; flexor margin ending in pair of spines preceded by 7-9 slender spines on distal half on P2, 6 or 7 on P3, 5 or 6 on P4. Dactyli proximally curved, 0.7 × length of carpi on P2 and P3, 0.95 × on P4, 0.4 × length of propodi on P2-4; flexor margin with 8 or 9 loosely arranged, obliquely directed, proximally diminishing spines, penultimate closer to ultimate than to antepenultimate.

Eggs. Number of eggs carried, 9; size, 1.30 mm × 1.77 mm - 1.33 mm × 1.58 mm.

REMARKS — The species resembles U. sagamiae Baba, 2005 and U. pollostadelphus n. sp. in having a pair of epigastric spines, in having the antennal articles 4 and 5 unarmed, and in having the P2-4 propodi with a row of flexor marginal spines distally ending in paired spines. Uroptychus benthaus is readily distinguished from U. sagamiae by the pterygostomian flap that is sharply angular anteriorly and produced to a distinct spine, instead of being roundish with a tiny spine; and P2-4 are more slender, e.g., the P2 merus being at least 6.6 instead of 3.7 times longer than broad. The relationships with U. pollostadelphus are discussed under the remarks of that species (see below).

Figures

FIGURE 32 Uroptychus benthaus n. sp., holotype, male 4.6 mm (MNHN-IU-2014-16327).A, carapace and anterior part of abdomen, proximal part of left 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, left P1, proximal part omitted, dorsal. Scale bars: 1 mm.

FIGURE 33 Uroptychus benthausn.sp.,holotype,male 4.6 mm (MNHN-IU-2014-16327).A,left P2,lateral.B, same,distal part,setae omitted,lateral.C, right P3, setae omitted, lateral. D, right P4,setae omitted, lateral. Scale bars:1 mm.