Uroptychus cylindropus, 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 : 152-155

Uroptychus cylindropus n. sp.

Figures 61 , 62

TYPE MATERIAL — Holotype: New Caledonia, Norfolk Ridge. SMIB 8 Stn DW 156, 24°46’S, 168°08’E, 275-300 m, 28.I.1993, ov. ♀ 5.3 mm ( MNHN-IU-2014-16370 ) . Paratypes: New Caledonia, Loyalty Islands. MUSORSTOM 6 Stn DW 483, 21°19.80’S, 167°47.80’E, 600 m, 23.II.1989, 1 ♂ 4.2 mm (MNHN-IU-2014-16371). New Caledonia, Norfolk Ridge. NOR- FOLK 1 Stn DW 1689, 24°54’S, 168°23’E, 600-620 m, 23.VI.2001, 1 ♀ 5.5 mm (MNHN-IU-2014-16372). NORFOLK 2 Stn DW 2064, 25°16.59’S, 168°55.64’E, 609-691 m, 26.X.2003, 1 ov. ♀ 4.8 mm (MNHN-IU-2014-16373) . – Stn CP2089, 24°44’S, 168°09’E, 227-230 m, 29.X.2003, 4 ♂ 4.9-5.7 mm, 1 ov. ♀ 4.9 mm, 1 ♀ 5.4 mm (MNHN-IU-2014-16374).

ETYMOLOGY„ The specific name is a noun in apposition from the Greek kylindros (a cylinder) and pous (a foot), referring to subcylindrical pereopods of the species.

DISTRIBUTION„ Loyalty Islands and Norfolk Ridge; 227- 691 m.

SIZE„ Males, 4.2-5.7 mm, females 4.8-5.5 mm; ovigerous females from 4.8 mm.

DESCRIPTION„ Medium-sized species. Carapace: As long as broad; greatest breadth 1.8 × distance between ordinary places of anterolateral spines. Dorsal surface with very fine setae discernible only under high magnification, convex from side to side, with very weak depression lateral to cardiac region, dorsal midline very slightly convex in profile continuing onto rostral dorsum. Lateral margins anteriorly rounded, with no distinct anterolateral angle and no anterolateral spine, somewhat divergent posteriorly to point one-third from anterior end, then convexly divergent further posteriorly. Rostrum elongate sharp triangular, with interior angle of 15°, nearly horizontal but slightly arched in profile, 2.5 × longer than broad, 0.7-0.8 × length of remaining carapace, breadth less than half carapace breadth measured at posterior carapace margin; dorsal surface flattish proximally, somewhat convex from side to side, with very fine short setae. Lateral limit of orbit with small spine. Pterygostomian flap anteriorly angular, produced to small, often blunt spine; surface smooth.

Sternum: Excavated sternum blunt triangular or convex on anterior margin, and smooth on surface. Sternal plastron slightly shorter than broad; sternite 5 as broad as or slightly narrower than sternite 4, narrower than sternit 6. Sternite 3 moderately depressed; anterior margin deeply excavated, representing broad V-shape, with no median notch and no median spines, anterolateral angle rounded. Sternite 4 with anterolateral margin well convex, without spine; posterolateral margin as long as anterolateral margin. Anterolateral margin of sternite 5 stongly convex, two-thirds length of posterolateral margin of sternite 4.

Abdomen: Smooth, nearly glabrous, long relative to breadth. Somite 1 antero-posteriorly convex, without distinct transverse ridge. Somite 2 tergite 1.9-2.2 × broader than long; lateral margin concavely divergent posteriorly, ending in rounded terminus. Pleuron of somite 3 bluntly produced. Telson slightly more than half as long as broad; posterior plate 1.3-1.4 × longer than anterior plate, posterior margin slightly concave or transverse medially.

Eye: Relatively short (length 1.6-1.7 × breath), falling short of proximal third of rostrum, mesial margin slightly concave, lateral margin slightly convex. Cornea not dilated, length about half that of remaining eyestalk.

Antennule and antenna: Ultimate antennular article 3.5-4.0 × longer than high. Antennal peduncle terminating in midlength of rostrum. Article 2 without lateral spine. Antennal scale slightly broader than article 5, falling short of distal end of article 4. Distal 2 articles unarmed; article 5 subequal to or slightly longer than article 4, breadth less than half height of antennular ultimate article. Flagellum consisting of 7-9 segments, not reaching rostral tip and distal end of P1 merus.

Mxp: Mxp1 with bases broadly separated. Mxp3 basis without denticles on mesial ridge. Ischium without distinct denticles on crista dentata, flexor margin not rounded distally. Merus 2.1 × longer than ischium, relatively thick mesiolaterally, unarmed. Carpus also unarmed.

P1: Slender (more so in females than in males), subcylindrical on merus and carpus, 5.0-5.6 × longer than carapace, covered with very short fine setae. Ischium with very small, often obsolescent dorsal spine, unarmed elsewhere. Merus 1.1-1.2 × longer than carapace. Carpus 1.3-1.4 × (males), 1.6-1.8 × (females) longer than merus. Palm 3.8-4.0 × (males), 7.0-9.0 × (females) longer than broad, slightly longer than or as long as carpus, moderately depressed. Fingers gaping (strongly gaping in males), setose on gaping portions and ventral surface, ending in small incurved spine, and distally slightly crossing, not spooned; movable finger with subtriangular process at one-third from proximal end (or at midlength of opposable margin in largely gaping fingers), length 0.3 × (females) or 0.4 × (males) that of palm; in females, fixed finger with opposable margin denticulate on distal third of length, fitting to opposite denticulate margin of movable finger when closed. P2-4: Relatively short, subcylindrical, meri and carpi with sparse short fine setae. Meri unarmed, longest on P2, shortest on P3, equally broad on P2-4; length-breadth ratio, 4.5-4.7 on P2, 3.2-3.7 on P3, 3.9-4.2 on P4; P2 merus 0.6-0.7 × length of carapace, 1.1-1.2 × length of P2 propodus; P3 merus 0.7 × as long as P2 merus, 0.7 × length of P3 propodus; P4 merus 1.1-1.3 × length of P3 merus, 0.8-0.9 × length of P4 propodus. Carpi subequal on P2-4, unarmed; length about one-third that of propodi. Propodi longer on P4 than on P2 and P3; length 4.5-5.4 × breadth on P2, 4.6-5.8 × on P3, 5.4- 5.9 × on P4; somewhat curving along flexor margin, sparsely setose; flexor margin with single terminal spine occasionally obsolete. Dactyli moderately curved, length about two-thirds that of propodus (in holotype, dactylus-propodus length ratio, 0.72-0.73 on P2, 0.61-0.66 on P3, 0.60-0.63 on P4), and 2 × longer than carpi on P2-4; flexor margin very setose, with 9-10 loosely arranged, sharp spines nearly perpendicular to margin, proximally diminishing, ultimate much more slender and shorter than penultimate.

Eggs. Number of eggs carried, 8-11; size, 1.04 mm × 1.08 mm - 1.32 mm × 1.56 mm.

REMARKS — Pereopod 1 in the new species shows sex-related differences: the palm length-breadth ratio is greater in females than in males (7.0-8.8 versus 3.8-3.9); the carpus-merus length ratio is greater in females than in males (1.7-1.8 versus 1.3-1.4), as also is the dactylus-palm length ratio greater in males than in females (0.4 versus 0.3).

The species is differentiated from all other known species of the genus by the absence of the anterolateral spine of the carapace, and by the very long rostrum, subcylindrical pereopods, and the P3 merus that is much shorter than the P2 merus as well as P4 merus.

Figures

FIGURE 61 Uroptychus cylindropus n.sp.,holotype,ovigerous female 5.3 mm (MNHN-IU-2014-16370).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,ventral. G, same, lateral.H, left P1, dorsal. Scale bars:1 mm.

FIGURE 62 Uroptychus cylindropus n. sp., holotype, ovigerous female 5.3 mm (MNHN-IU-2014-16370). A, right P2, lateral. B, same, distal part, lateral. C, right P3, lateral. D, right P4, lateral. Scale bars: 1 mm.