Uroptychus smib, 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 : 484-486

Uroptychus smib n. sp.

Figures 242 , 243

TYPE MATERIAL — Holotype: New Caledonia, Norfolk Ridge. SMIB 5 Stn DW 103, 23°16’S, 168°04’E, 300-315 m, 14.IX.1989, ov. ♀ 2.9 mm ( MNHN-IU-2013-8520 ).

ETYMOLOGY„ Named for the SMIB 5 cruise by which the new species was collected; used as a noun in apposition.

DISTRIBUTION„ Norfolk Ridge; 315 m.

DESCRIPTION„ Small species. Carapace: 1.1 × broader than long (0.9 × as long as broad); greatest breadth 2.0 × distance between anterolateral spines. Dorsal surface moderately convex from anterior to posterior, with weak depression between gastric and cardiac regions; very small tubercle-like spines or denticles scattered on anterior gastric and hepatic regions. Lateral margins convex and moderately divergent posteriorly; anterolateral spine well developed, directly lateral to ill-defined lateral limit of orbit; 6 small spines on branchial margin, last one situated at midlength of posterior branchial margin, followed by ridge leading to posterior end. Rostrum relatively broad triangular, with interior angle of 40°, length one-third that of remaining carapace, breadth slightly less than half carapace breadth at posterior carapace margin; dorsal surface nearly straight, horizontal, and moderately concave; lateral margin with small subapical spine on left side, absent on right side. Pterygostomian flap anteriorly somewhat roundish, with very small spine at anterior end and a few small spines on anterior surface.

Sternum: Excavated sternum anteriorly narrow triangular, surface cristate on anterior half in midline. Sternal plastron 1.4 × broader than long, lateral extremities straight divergent posteriorly. Sternite 3 shallowly depressed, relatively short; anterior margin moderately concave, with 2 small submedian spines separated by shallow notch. Anterolateral margin of sternite 4 somewhat convex, anteriorly produced to anterolaterally directed short spine, 1.4 × longer than posterolateral margin. Anterolateral margin of sternite 5 slightly convexly divergent posteriorly, slightly longer than posterolateral margin of sternite 4.

Abdomen: Glabrous and polished. Somite 1 without transverse ridge. Somite 2 tergite 1.9 × broader than long; pleuron blunt on anterolateral and posterolateral ends, lateral margin feebly concave and strongly divergent posteriorly. Pleuron of somite 3 with blunt lateral terminus. Telson about half as long as broad; posterior plate 1.8 × longer than anterior plate, posterior margin feebly concave.

Eye: Elongate, 2 × longer than broad at base, distally narrowed, reaching apex of rostrum. Cornea much less than half as long as remaining eyestalk.

Antennule and antenna: Ultimate article of antennule 2.7 × longer than high. Antennal peduncle overreaching rostrum, relatively slender. Article 2 with small distolateral spine. Antennal scale 1.4 × broader than article 5, ending in midlength of that article. Distal 2 articles each with distomesial spine. Article 5 2.7 × longer than article 4, breadth about half height of antennular ultimate article. Flagellum consisting of 12 segments.

Mxp: Mxp1 with bases nearly contiguous. Mxp3 barely setose on lateral surface. Basis with 3 denticles on mesial ridge. Ischium with 16 (left) or 18 (right) denticles on crista dentata, flexor margin distally not rounded. Merus 2.6 × longer than ischium, flexor margin not well ridged, lateral surface with 1 spine close to distal end of flexor margin and another spine at proximal third (between flexor and extensor margins); distolateral spine distinct. Carpus with distolateral spine and another spine on proximal part of extensor margin.

P1: Missing.

P2-4: Slender, compressed mesio-laterally, sparsely setose on meri and carpi, more setose on distal articles. Meri successively shorter posteriorly (P3 merus 0.9 × length of P2 merus, P4 merus 0.8 × length of P3 merus); P2-3 meri equally broad; P4 merus slightly narrower than P3 merus; length-breadth ratio, 5.2 on P2, 4.7 on P3, 4.2 on P4; P2 merus about as long as carapace, 1.1 × longer than P2 propodus; P3 merus about as long as P3 propodus; P4 merus 0.9 × length of P4 propodus; dorsal margins with a few very small spines on proximal portion on P2 and P3, smooth on P4. Carpi unarmed, successively shorter posteriorly; carpus-propodus length ratio, 0.6 on P2-4, much longer than dactyli (carpus-dactylus length ratio, 1.9 on P2, 1.7 on P3, 1.6 on P4). Propodi subequal in length on P2 and P3, shorter on P4; flexor margin somewhat convex distally in lateral view, with pair of terminal spines preceded by row of spines closely arranged distally, loosely arranged proximally, proximalmost situated at point proximal third and remotely equidistant between proximal second and proximal end of article. Dactyli subequal, about one-third as long as propodi, much shorter than carpi (dactylus-carpus length ratio, 0.5 on P2, 0.6 on P3 and P4), moderately curving; extensor margin with row of plumose setae; flexor margin ending in slender spine preceded by 8-9 proximally diminishing, somewhat inclined sharp spines, penultimate and antepenultimate subequal and distinctly larger than ultimate.

Eggs. Number of eggs carried, 5; size, 0.9-1.0 mm × 1.0- 1.1 mm.

REMARKS — The spination of both the carapace and the P2-4 dactyli displayed by the new species is similar to that of U. lanatus n. sp. (see above). Uroptychus smib is differentiated from U. lanatus by the ill-defined lateral orbital angle, the elongate eyes, the short antennal scale terminating in midlength of the ultimate article, sternite 3 having a pair of median spines on the anterior margin, and P2-4 being more slender and propodi much longer relative to dactyli.

Figures

FIGURE 242 Uroptychus smib n.sp.,holotype,ovigerous female 2.9 mm (MNHN-IU-2013-8520).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, right antenna,ventral.F, right Mxp3,setae omitted, ventral.G, same,setae omitted, lateral. Scale bars: 1 mm.

FIGURE 243 Uroptychus smib n. sp., holotype,ovigerous female 2.9 mm (MNHN-IU-2013-8520).A, left P2, lateral.B, same,distal part, lateral.C, left P3, setae omitted, lateral.D, left P4, setae omitted,lateral.Scale bars:1 mm.