Uroptychus alophus, 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 : 53-57

Uroptychus alophus n. sp.

Figures 10 , 11

TYPE MATERIAL — Holotype: New Caledonia, Chesterfield Islands . MUSORSTOM 5 Stn DW 272, 24°40.91’S, 159°43.00’E, 500-540 m, 9.X.1986, 1 ♀ 3.7 mm ( MNHN-IU-2014-17276 ) . Paratypes: New Caledonia, Chesterfield Islands. Station data as for the holotype, 2 ♂ 2.6, 3.4 mm, 1 ov. ♀ 3.0 mm, 2 ♀ 3.5, 3.5 mm (MNHN-IU-2014-17277). New Caledonia, Norfolk Ridge. BIOCAL Stn CP 52, 23°06’S, 167°47’E, 540-600 m, 31.VIII.1985, 1 ♂ 4.1 mm (MNHN-IU-2014-17278). BATHUS 3 Stn DW 817, 23°42’S, 168°16’E, 405-410 m, 28.XI.1993, 1 ♂ 3.3 mm (MNHN-IU-2014-17279). CHALCAL 2 Stn CC 01, 24°54.96’S, 168°21.91’E, 500-580 m, 28.X.1986, 1 ov. ♀ 4.7 mm (MNHN-IU-2014-17280). NORFOLK 2 Stn DW 2041, 23°40.93’S, 168°01.29’E, 400 m, 23.X.2003, 6 ♂ 2.9-4.8 mm, 2 ov. ♀ 3.2, 3.5 mm (MNHN-IU-2014-17281) . – Stn DW2042, 23°40.51’S, 168°00.58’E, 235-245 m, 23.X.2003, 1 ov. ♀ 3.7 mm (MNHN-IU-2014-17282) . – Stn CP2083, 24°53.23’S, 168°21.86’E, 530-540 m, 28.X.2003, 3 ♂ 4.0- 4.4 mm (MNHN-IU-2014-17283).

ETYMOLOGY„ From the Greek lophos (ridge) with suffix a -, meaning without ridge, referring to the absence of sharp transverse ridge on the first abdominal tergite by which the species is readily distinguished from the related species, U. longior Baba, 2005 .

DISTRIBUTION„ Chesterfield Islands and Norfolk Ridge; 235- 600 m.

SIZE„ Males, 2.6-4.8 mm; females 3.0- 4.7 mm; ovigerous female from 3.0 mm.

DESCRIPTION — Small species. Carapace: Somewhat broader than long (0.9 × as long as broad); greatest breadth measured between bases of last lateral marginal spines, 1.6 × distance between anterolateral spines. Dorsal surface polished, somewhat convex from anterior to posterior, without distinct groove; with sparse short setae. Lateral margins weakly convex, usually with 8 (rarely 9) spines; first anterolateral, reaching tip of smaller lateral orbital spine; second and third small; remainder acute, posteriorly diminishing, fourth situated at anterior end of branchial region, mesially accompanying 1 or 2 small spines, last followed by ridged margin. Rostrum broad triangular, with interior angle of 25-28°, horizontal; length about half that of remaining carapace (two-thirds in paratype MNHN-IU-2014-17282), breadth half carapace breadth measured at posterior carapace margin; dorsal surface somewhat concave; lateral margin with a few distinct or indistinct small spines distally (7 spines in one of male paratypes MNHN-IU-2014-17281). Lateral orbital spine relatively close to but distinctly anterior to level of anterolateral spine. Pterygostomian flap with anterior margin produced to acute spine followed by a few spines along anterior part of linea anomurica.

Sternum: Excavated sternum blunt triangular on anterior margin, bearing distinct (often sharp) ridge in midline of surface. Sternal plastron slightly broader than long, lateral extremities gently divergent posteriorly. Sternite 3 moderately depressed; anterior margin weakly concave, with broad U-shaped median sinus separating 2 small spines; anterolateral angle rounded or sharply angular. Sternite 4 with anterolateral margin slightly longer than posterolateral margin, moderately or slightly convex, or straight, anteriorly ending in pronounced process occasionally with accompanying small spine directly lateral and/or mesial to it. Anterolateral margin of sternite 5 moderately convex, about as long as posterolateral margin of sternite 4.

Abdomen: Smooth. Somite 1 moderately convex from anterior to posterior. Somite 2 tergite 2.3-2.7 × broader than long; pleuron rounded on anterolateral and posterolateral ends, somewhat concave on lateral margin. Pleuron of somite 3 laterally blunt. Telson 0.4-0.5 × as long as broad; posterior plate distinctly or slightly emarginate on posterior margin, length 1.2-1.4 × that of anterior plate.

Eye: about 2 × longer than broad, overreaching midlength of rostrum, lateral and mesial margins subparallel. Cornea not dilated, length about half or more than half that of remaining eyestalk.

Antennule and antenna: Antennular ultimate article 2.8-3.3 × longer than high. Antennal peduncle distinctly overreaching cornea, not reaching apex of rostrum. Article 2 with small, distinct spine. Antennal scale 1.5-1.7 × broader than article 5, reaching or slightly overreaching tip of distal spine of article 5, reaching or slightly falling short of apex of rostrum. Distal 2 articles each with strong distomesial ventral spine; article 5 1.7-2.0 × longer than article 4, breadth 0.7-0.8 × height of antennular ultimate article. Flagellum of 8-11 segments barely reaching distal end of P1 merus.

Mxp: Mxp1 with bases separated. Mxp3 basis with 1 denticle near distal end of mesial ridge. Ischium with 14-23 denticles on crista dentata; flexor margin sharply crested, rounded distally. Merus 2.1 × longer than ischium, flattish and smooth on mesial face; flexor margin well ridged with a few to several small, occasionally obtuse spines on distal half; distolateral spine distinct, occasionally accompanying additional small spine. Carpus with distolateral spine and a few small spines on extensor margin.

P1: 4 × longer than carapace; relatively massive and setose. Ischium dorsally with sharp, procurved distal spine occasionally followed by small spine, ventromesially with well-developed, subterminal spine occasionally distantly followed by a few small proximal spines. Merus mesially with a few spines of moderate size, laterally unarmed, dorsally with 2 or 3 rows of spines usually small, often obsolete, ventrally with 2 rows of spines and well-developed distomesial and distolateral spines; length subequal to that of carapace. Carpus subequal to or slightly longer than merus, dorsally with 2-3 rows of spines continued from merus, ventrally with well-developed distomesial and distolateral spines. Palm 2.1-2.5 × longer than broad, about as long as carpus, somewhat depressed, unarmed. Fingers curved slightly ventrally, relatively broad, distally ending in slightly incurved spine, crossing when closed; denticulate opposable margins sinuous (proximal obtuse process of movable finger fitting to between 2 eminences on immovable finger when closed), not spooned; movable finger 0.6-0.7 × length of palm.

P2-4: Compressed mesio-laterally, moderately setose, broad relative to length, meri in particular. Meri successively shorter posteriorly (P3 merus 0.9-1.0 × length of P2 merus, P4 merus 0.8-0.9 × length of P3 merus), subequal in breadth on P2-4; length-breadth ratio, 2.8-3.2 on P2, 2.6-2.9 on P3, 2.3-2.5 on P4; P2 merus 0.7 × length of carapace, 0.7-0.9 × length of P2 propodus; P3 merus 0.8 × length of P3 propodus; P4 merus 0.7-0.8 × length of P4 propodus; extensor margin with row of spines continued onto carpus, distinct on P2 and P3, obsolescent on P4; ventrolateral margin with 1 or 2 distal spines on P2-4. Carpi subequal, carpus-propodus length ratio, 0.4 on P2 and P3, 0.3-0.4 on P4; extensor margin with row of small spines, distalmost somewhat larger, with smaller or subequal-sized accompanying spine lateral to it (another row of a few spines lateral to extensor row in male paratype of MNHN-IU-2014-17281). Propodi slightly longer on P3 than on P2 and P4 or subequal on P3 and P4 and somewhat shorter on P2; extensor margin with a few proximal spines distinct on P2 and P3 but occasionally obsolete; flexor margin ending in pair of spines preceded by 1-3 spines on P2, 0 or 1 on P3-4. Dactyli shorter on P2 than on P3 and P4, subequal on P3 and P4; distinctly longer than carpi (dactylus-carpus length ratio, 1.5 on P2, 1.6 on P3 and P4) and more than half length of propodi (dactylus-propodus length ratio, 0.6-0.7 on P2 and P3, 0.6 on P4), proportionately broad; flexor margin nearly straight, with 9-13 (usually 9) spines obliquely directed and close (nearly contiguous) to each other, ultimate slender, smaller than antepenultimate, penultimate prominent, about twice as broad as antepenultimate.

Eggs. Up to 25 eggs carried; size, 0.80 mm × 0.94 mm - 1.15 mm × 1.19 mm.

Color. P1 with orangish bands in preservative, 1 on merus, 2 on each of carpus and palm ( Figure 11A ).

REMARKS„ The arrangements of spines on the carapace and P2-4, the shape of sternal plastron, and the long antennal scale are very similar to those of U. longior Baba, 2005 . However, the new species has a low instead of sharp transverse ridge on the abdominal somite 1; P1 is much broader and shorter, with the merus as long as instead of distinctly longer than the carapace; the P1 carpus bears a pronounced instead of small distomesial spine.

The rostrum having a few very small lateral spines, the carapace lateral margin spinose, and the P2-4 dactyli well compressed mesio-laterally, with obliquely directed spines on the flexor margin suggest that U. alophus n. sp. is close to U. nanophyes McArdle, 1901 . The new species is distinguished from that species by more pronounced spines on the carapace lateral margin; the anterolateral spine of sternite 4 is very short instead of reaching the anterior end of sternite 3; and no row of ventromesial spines is present on the P2 merus.

Figures

FIGURE 10 Uroptychus alophus n. sp., holotype, female 3.7 mm (MNHN-IU-2014-17276).A, carapace and anterior part of abdomen, dorsal. B, same, lateral. C, sternal plastron, excavated sternum included. D, telson. E, right antenna, ventral. F, left Mxp3, setae omitted, ventral.G, same, lateral.Scale bars: 1 mm.

FIGURE 11 Uroptychus alophus n. sp.,holotype,female 3.7 mm (MNHN-IU-2014-17276).A, left P1,dorsal.B, right P1,proximal part,ventral.C, right P2, lateral. D, same, distal part, setae omitted, lateral.E, right P3,lateral.F, right P4, lateral. Scale bars: 1 mm.