Uroptychus obtusus, 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 : 363-366

Uroptychus obtusus n. sp.

Figures 178 , 179

TYPE MATERIAL — Holotype: New Caledonia, Norfolk Ridge. NORFOLK 2 Stn DW 2049, 23°42.88’S, 168°15.43’E, 470- 621 m, 24.X.2003, ♂ 2.6 mm ( MNHN-IU-2014-16832 ).

ETYMOLOGY„ From the Latin obtusus (blunt, dull), alluding to distomesial spines of antennal articles 4-5 that are distally blunt, not sharp as in other species, characteristic of the new species.

DISTRIBUTION„ Norfolk Ridge; 470- 621 m.

DESCRIPTION — Carapace 1.4 × as broad as long; greatest breadth 1.4 × distance between anterolateral spines. Dorsal surface nearly horizontal in profile on gastric region; cardiac and branchial regions somewhat inflated; hepatic and branchial regions with very tiny spines laterally (1 slightly larger spine directly behind anterolateral spine on right side in holotype). Lateral margins convex on hepatic region, and again well convex on branchial region; anterolateral spine strong, directed straight forward, extending far beyond antennal article 2, reaching midlength of cornea. Rostrum horizontal, with interior angle of 30°, dorsally excavated, laterally slightly convex, with denticle-like small spines distally; length about three-quarters that of remaining carapace, breadth half carapace breadth at posterior carapace margin. Lateral orbital spine very small, situated at same level as anterolateral spine. Pterygostomian flap anteriorly produced to strong spine reaching distal end of cornea; surface with tubercle-like spines.

Sternum: Excavated sternum with sharp ridge in midline, anteriorly subtriangular between bases of Mxp1. Sternal plastron slightly shorter than broad, sternites successively broader posteriorly. Sternite 3 well depressed, anterolaterally angular; anterior margin very weakly excavated, with deep narrow median notch. Sternite 4 having anterolateral margin very weakly divergent posteriorly, about as long as posterolateral margin, anterior end rounded or bluntly angular. Sternite 5 with anterior lobe smaller than posterior lobe.

Abdomen: Glabrous. Somite 1 antero-posteriorly convex. Somite 2 tergite 2.7 × broader than long; pleuron with slightly concave lateral margin very weakly divergent posteriorly, ending in blunt tip. Pleuron of somite 3 laterally blunt. Telson half as long as broad; posterior plate moderately emarginate, length 1.4 × that of anterior plate.

Eye: Short relative to breadth (1.4-1.5 × longer than broad), ending in midlength of rostrum, slightly broadened at midlength. Cornea not dilated, slightly more than half as long as remaining eyestalk.

Antennule and antenna: Ultimate article of antennular peduncle 3 × longer than high. Antennal peduncle overreaching cornea by length of article 5. Article 2 fused with antennal scale, with blunt spine at ordinary place of distolateral margin. Antennal scale with 2 small, blunt lateral spines, slightly overreaching midlength of article 5, breadth 1.5 × that of article 5. Articles 4 with blunt distomesial spine ventrally. Article 5 produced ventrodistally into bluntly truncate mesial spine reaching second segment of antennal flagellum, bearing a few small spines in ventral midline; length 1.3 × that of article 4, breadth three-quarters height of antennular ultimate article. Flagellum consisting of 8 segments, falling short of distal end of P1 merus.

Mxp: Mxp1 with bases broadly separated. Mxp3 basis with 4 or 5 obsolescent denticles on mesial ridge. Ischium with 7 or 8 obsolescent denticles on crista dentata, flexor margin distally rounded. Merus about 3 × longer than ischium, flexor margin not cristate but roundly ridged, bearing 2 blunt spines in distal third; distolateral spine distinct. Carpus with distolateral spine and small extensor proximal spine, and another small spine between.

P1: Subcylindrical, scarcely setose, length 8.6 × that of carapace. Ischium dorsally with strong spine, ventrally with a few tubercle-like proximal spines only. Merus 1.7 × longer than carapace; dorsally with spines arranged roughly in 2 longitudinal rows; ventrally with distolateral and distomesial spines, and a few proximal spines; mesially with a few strong spines. Carpus narrower than merus, covered with very small spines, distally lacking ventrolateral and ventromesial spines; length 1.8 × that of merus. Palm 4.7 × longer than broad, 0.9 × length of carpus, bearing tubercle-like spines on proximal part of dorsal surface, smooth elsewhere. Fingers with relatively short, sparse setae, tips slightly incurved, crossing when closed; opposable margin of fixed finger sinuous; that of movable finger with lobe-like process at proximal third fitting to longitudinal groove on opposite face of fixed finger when closed; length 0.4 × that of palm.

P2-4: Right P2 and P3 missing. Relatively thick, barely setose except for dactyli. Meri equally broad on P2-4, subequal in length on P2 and P3, shortest on P4 (P4 merus 0.8 × length of P3 merus); length-breadth ratio, 3.2 on P2 and P3, 2.6 on P4; dorsal margin dully crested, with row of short spines (10 on P2 and P3, 7 on P4) continued onto carpi; ventral surface more or less flattish; ventrolateral margin with terminal spine distinct on P2 and P3, obsolete on P4; P2 merus 0.9 × length of carapace, slightly shorter than P2 propodus; P3 merus 0.8 × length of P3 propodus; P4 merus 0.7 × length

of P4 propodus. Carpi subequal on P2-4, length less than half that of propodi (carpus-propodus length ratio, 0.4 on P2 and P3, 0.3 on P4); extensor margin with 6 spines subparalleling 4 or 5 smaller spines on lateral surface. Propodi shorter on P2 than on P3 and P4; extensor margin with 1 or 2 small spines proximally; flexor margin straight on P2 and P3, slightly concave on P4, bearing pair of terminal spines only. Dactyli shorter on P2 than on P3 and P4, subequal on P3 and P4; length much more than that of carpi (dactylus-carpus length ratio, 1.5 on P2 and P3, 1.7 on P4) and 0.6 that of propodi; flexor margin nearly straight, with short, broad penultimate spine preceded by much smaller, obliquely directed, blunt, very closely arranged spines, ultimate spine very slender and shorter than penultimate; penultimate spine 1.5 × broader than antepenultimate; extensor margin fringed with plumose setae.

REMARKS — The spination of pereopods in the new species is very similar to that of U. vulcanus n. sp. Their relationships are discussed under the account of that species (see below).

Figures

FIGURE 178 Uroptychus obtusus n. sp.,holotype,male 2.6 mm (MNHN-IU-2014-16832).A, carapace and anterior part of abdomen,proximal parts of P1 included, 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, lateral.H, left P1, dorsal.Scale bars:1 mm.

FIGURE 179 Uroptychus obtusus n.sp.,holotype,male 2.6 mm (MNHN-IU-2014-16832).A, left P2,lateral.B, same,distal part,setae omitted,lateral.C, left P3,setae omitted,lateral. D, same, distal part, lateral. E, left P4, lateral.F, same, distal part, lateral. Scale bars: 1 mm.