Uroptychus minor, 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 : 319-322

Uroptychus minor n. sp.

Figures 152 , 153

TYPE MATERIAL — Holotype: New Caledonia. BIOCAL Stn DW 51, 23°05’S, 167°45’E, 680-700 m, 31.VIII.1985, ♂ 2.2 mm ( MNHN-IU-2013-8518 ) . Paratypes: New Caledonia. Collected with holotype, 2 ♂ 1.6, 2.3 mm (MNHN-IU-2014-16730). CALSUB Dive PL 20, 22°53,7’S, 167°23’E, 616- 555 m, 10.III.1989, 2 ♀ 1.6, 2.1 mm (MNHN-IU-2014-16731). MUSORS- TOM 4 Stn DW 151, 19°07.0’S, 163°22.0’E, 200 m, 14.IX.1985, 1 ♀ 2.0 mm (MNHN-IU-2014-16732) . – Stn DW 197, 18°51’S, 163°21’E, 560 m, 20.IX.1985, 1 ♀ 2.4 mm (MNHN-IU-2014-16733). SMIB 6 Stn DW 123, 18°56.6’S, 163°25.0’E, 330-360 m, 3.III.1990, 1 ov. ♀ 2.6 mm (MNHN-IU-2014-16734). BATHUS 4 Stn DW 924, 18°54.85’S, 163°24.34’E, 344- 360 m, 7.VIII.1994, 1 ♀ 2.4 mm (MNHN-IU-2014-16735). New Caledonia, Norfolk Ridge. SMIB 4 Stn DW 55, 23°21’S, 168°05’E, 215-260 m, 09.III.1989, 1 ♂ 2.0 mm, 2 ov. ♀ 1.5, 1.6 mm (MNHN-IU-2014-16736) . – Stn DW 57, 23°21’S, 168°04’E, 210-260 m, 09.III.1989, 1 ♂ 1.7 mm (MNHN-IU-2014-16737). New Caledonia, Chesterfield Islands . MU- SORSTOM 5 Stn DW 308, 22°09’S, 159°23’E, 450-635 m, 12.X.1986, 1 ♀ 2.4 mm (MNHN-IU-2014-16738). EBISCO Stn DW 2606, 19°36.0’S, 158°42.0’E, 442-443 m, 18.X.2005, 1 ♀ 3.0 mm (MNHN-IU-2014-16739) .

ETYMOLOGY„ From the Latin minor (smaller), alluding to the small size of the species.

DISTRIBUTION„ New Caledonia, Norfolk Ridge and Chesterfield Islands; 200- 700 m.

SIZE„ Males, 1.6-2.3 mm; females, 1.5-3.0 mm; ovigerous females from 1.5 mm.

DESCRIPTION„ Small species. Body elongate and subcylindrical. Carapace: Much longer than broad (1.3-1.4 × longer); greatest breadth 1.4 × distance between anterolateral spines. Dorsal surface strongly convex from side to side, nearly straight from anterior to posterior, feebly depressed on gastric-cardiac and gastric-branchial boundaries; sparsely or moderately with short fine setae. Lateral margins slightly divergent posteriorly or slightly convex medially, with row of very fine, short, oblique ridges often barely discernible; anterolateral spine slightly overreaching smaller lateral orbital spine. Rostrum very short, broad triangular, with interior angle of 46-48°, slightly deflected ventrally, varying from barely reaching to slightly overreaching midlength of eye, never reaching cornea, length 0.12-0.27 × that of remaining carapace, breadth half carapace breadth at posterior carapace margin. Lateral orbital spine small, situated directly mesial to anterolateral spine. Pterygostomian flap anteriorly angular, produced to distinct spine, smooth on surface.

Sternum: Excavated sternum with sharp ridge in ventral midline, anterior margin subtriangular. Sternal plastron 1.2 × longer than broad. Sternite 3 strongly depressed, anterolateral angle sharply produced anteriorly, anterior margin of broad V-shape with or without small median notch. Sternite 4 as broad as sternite 6, anterolateral margin slightly convex, anteriorly angular; posterolateral margin 0.7 × length of anterolateral margin. Sternite 5 narrower than sternite 4, anterolateral margin roundly produced anteriorly, about as long as posterolateral margin of sternite 4. Sternite 7 broader than sternite 6.

Abdomen: Somites long relative to breadth, covered with short fine setae. Somite 1 without transverse ridge. Somite 2 tergite 1.8-2.2 × broader than long; pleuron posterolaterally rounded, lateral margins feebly concave and nearly subparallel. Pleura of somites 3 and 4 with rounded lateral margin. Telson slightly more than half as long as broad; posterior plate semicircular, not emarginate on posterior margin, length 1.2-1.7 × that of anterior plate.

Eye: Elongate (1.7 × longer than broad), overreaching rostrum, broad relative to carapace breadth, one-third as broad as distance between anterolateral spines of carapace; lateral and mesial margins somewhat convex. Cornea not dilated, length about half that of remaining eyestalk.

Antennule and antenna: Ultimate article of antennular peduncle 2.3-2.7 × longer than high. Antennal peduncle extending far beyond eyes. Article 2 with very small distolateral spine. Antennal scale slightly broader than article 5, proportionately broad distally, terminating in midlength of article 5. Distal 2 articles unarmed; article 5 1.5 × longer than article 4, breadth slightly less than half height of ultimate article of antennule. Flagellum of 7-11 segments barely reaching distal end of P1 merus.

Mxp: Mxp1 with bases broadly separated. Mxp3 sparsely setose on lateral surfaces of merus and carpus. Basis without denticles on mesial ridge. Ischium with very small, rather obsolescent denticles on crista dentata; flexor margin rounded distally. Merus 2.3 × longer than ischium, moderately compressed mesio-laterally; flexor margin with a few very small denticles distal to point one-third from distal end. Carpus unarmed.

P1: Massive especially on palm, almost unarmed, 3.7-5.4 × longer than carapace, sparsely with short soft setae. Ischium dorsally bearing basally broad, short, blunt spine, ventrally unarmed but a few obsolescent tubercles on proximal mesial margin. Merus and carpus with weak short ridges supporting setae. Merus as long as or slightly longer than carapace. Carpus 1.1-1.5 × longer than merus. Palm 2.1-3.4 × longer than broad, 1.0-1.4 × length of carpus. Fingers more setose than proximal articles, distally incurved, crossing when closed; movable finger 0.4-0.6 × length of palm, opposable margin with low obtuse proximal process somewhat proximal to position of opposite low eminence on fixed finger.

P2-4: Slender, sparsely setose, unarmed on meri and carpi. Meri successively shorter posteriorly (P3 merus 0.7-0.8 × length of P2 merus, P4 merus 0.9 × length of P3 merus); breadths subequal on P2-4; length-breadth ratio, 3.9-4.0 on P2, 3.3 on P3, 2.8-2.9 on P4; P2 merus 0.7-0.8 × length of carapace, about as long as or slightly shorter than P2 propodus; P3 merus 0.8 × length of P3 propodus; P4 merus 0.7 × length of P4 propodus. Carpi subequal, much shorter than dactyli (carpus-dactylus length ratio, 0.7 on P2, 0.5-0.6 on P3 and P4); carpus-propodus length ratio, 0.4 on P2, 0.3-0.4 on P3, 0.3 on P4. Propodi shorter on P2 than on P3 and P4 and subequal on P3 and P4 or longer on P2 than on P3 and P4; propodusdactylus length ratio, 1.5-1.6 on P2-4; flexor margin nearly straight, ending in pair of spines preceded by 2 or 3 spines on P2, 1 spine on P3 and P4. Dactyli gently narrowed distally; dactylus-carpus length ratio, 1.4-1.5 on P2, 1.7-1.8 on P3 and P4; more than half length of propodi on P2-4; flexor margin slightly curving, ending in slender spine preceded by 8-12 spines, penultimate spine pronounced, more than twice broader than ultimate and antepenultimate spines, remaining spines slender and much shorter than ultimate, obliquely directed, closely arranged but not contiguous to one another, successively diminishing toward base of article.

Eggs. Number of eggs carried, 2-5; size; 0.7 mm × 0.8 mm - 0.9 mm × 1.0 mm.

REMARKS — The elongate, subcylindrical body with the short rostrum in the shape of an equilateral triangle is unique among the species of Uroptychus . It is interesting to note that the body size is small relative to the size of eggs. Two eggs carried by the smallest ovigerous female (1.5 mm) each measure two-thirds the greatest breadth of the carapace.

The elongate carapace is also possessed by U. lacunatus n. sp. (see above). However, U. lacunatus is characterized by the narrowly triangular rostrum overreaching the eyes, the anterolateral spine of the carapace well developed, extending far beyond the lateral orbital spine, the P2-4 carpi longer than the dactyli, and the dactyli having proximally diminishing spines on the flexor margin (the ultimate and penultimate subequal); all distinctive differences from U. minor .

Figures

FIGURE 152 Uroptychus minor n. sp., holotype, male 2.2 mm (MNHN-IU-2013-8518). A, carapace and abdomen, proximal part of right 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, setae omitted, ventral.G, same, lateral. H, right P1, proximal part, setae omitted, ventral.I, same, dorsal. Scale bars: 1 mm.

FIGURE 153 Uroptychus minor n. sp., holotype, male 2.2 mm (MNHN-IU-2013-8518). A, right P2, lateral. B, same, distal part, setae omitted, lateral.C, right P3, setae omitted,lateral.D, left P4,setae omitted, lateral. Scale bars:1 mm.