Uroptychus baeomma, 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 : 87-91

Uroptychus baeomma n. sp.

Figures 28 , 29

TYPE MATERIAL — Holotype: New Caledonia, Loyalty Islands. BIOCAL Stn DW 83, 20°35’S, 166°54’E, 460 m, 6.IX.1985, ov. ♀ 9.8 mm (MNHN-IU-2014-16310) . Paratypes: Station data as for the holotype, 1 ♂ 7.5 mm, 1 ♀ 5.0 mm ( MNHN- IU-2014-12786). New Caledonia, MUSORSTOM 4 Stn CP 216, 22°59.5’S, 167°22.0’E, 490-515 m, 29.IX.1985, 1 ♂ 7.6 mm, 3 ov. ♀ 9.7-10.0 mm, 1 ♀ 10.1 mm (MNHN-IU-2014-16311) . – Stn CP 238, 22°13.0’S, 167°14.0’E, 500-510 m, 2.X.1985, 1 ♂ 7.5 mm, 1 ov. ♀ 7.6 mm (MNHN-IU-2014-16312). New Caledonia, Hunter and Matthew Islands. VOL- SMAR Stn DW 16, 22°25’S, 171°41’E, 420-500 m, 03.VI.1989, 1 ♂ 4.7 mm, 1 ♀ 5.8 mm (MNHN-IU-2014-16313). Vanuatu. MUSORSTOM 8 Stn CP 974, 19°21.51’S, 169°28.26’E, 492-520 m, 22.IX.1994, 2 ov. ♀ 7.5, 7.8 mm ( MNHN- IU-2014-16314) . – Stn CP983, 19°21.61’S, 169°27.76’E, 480- 475 m, 23.IX.1994, 1 ov. ♀ 7.3 mm (MNHN-IU-2014-16315).

ETYMOLOGY„ The specific name is a noun in apposition from the Greek baios (small) and omma (eye), referring to relatively small corneae of the species.

DISTRIBUTION„ Loyalty Islands, New Caledonia, Hunter and Matthew Islands, and Vanuatu; 460- 520 m.

SIZE„ Males, 4.7-7.6; females, 5.0-10.0 mm; ovigerous females from 7.3 mm.

DESCRIPTION„ Medium-sized species. Carapace: Slightly broader than long (0.9 × as long as broad); greatest breadth 1.9-2.0 × distance between anterolateral spines. Dorsal surface smooth with scattered setae, slightly convex from anterior to posterior, with or without laterally diminishing cervical groove. Lateral margins well convex, with 5 well-developed spines on anterior two-thirds of length: first anterolateral, overreaching small lateral orbital spine, located at level of that spine; remaining 4 strong, situated on branchial region, directed anteriorly, somewhat diminishing posteriorly, third spine rarely preceded by small spine, last spine followed by distinct ridge leading to posterior end; 1-3 very small tubercle-like spines often obsolescent between first (anterolateral) and second spines. Rostrum broad triangular, with interior angle of 37°, slightly deflected ventrally, length about half or less than half that of remaining carapace, breadth less than half carapace breadth measured at posterior carapace margin; dorsal surface concave, ventral surface horizontal; lateral margin with subapical spine usually very small, often obsolescent. Pterygostomian flap with scattered small spines or tubercles on anterior portion, anterior margin sharply angular, terminating in distinct spine.

Sternites: Excavated sternum with strongly convex anterior margin between Mxp1, surface with weak broad longitudinal ridge in midline. Sternal plastron slightly broader than long; lateral extremities moderately divergent posterolaterally. Sternite 3 strongly depressed; anterior margin shallowly concave, with narrow, U-shaped median sinus flanked by distinct or indistinct spine, anterolaterally angular; lateral margin with small spine or process at midlength. Sternite 4 with anterolateral margin nearly entire, somewhat convex, anterolateral angle minutely denticulate, rounded or somewhat angular; posterolateral margin relatively short, about two-thirds of anterolateral margin. Anterolateral margin of sternite 5 strongly convex anteriorly, about as long as posterolateral margin of sternite 4.

Abdomen: Smooth, glabrous. Somite 1 feebly convex from anterior to posterior on dorsal surface. Somite 2 tergite 2.3- 2.5 × broader than long; pleuron with lateral margin slightly concave, anterolateral and posterolateral margins rounded. Pleuron of somite 3 laterally blunt. Telson 0.4 × as long as broad; posterior plate 1.2-1.4 × longer than anterior plate, posterior margin feebly convex, nearly transversal or feebly concave.

Eye: Relatively small, moderately elongate, about 2 × longer than broad, overreaching midlength of rostrum, slightly narrowed distally or with lateral and mesial margins subparallel. Cornea not inflated, about half as long as remaining eyestalk.

Antennule and antenna: Ultimate article of antennular peduncle 2.6-3.5 × longer than high. Antennal peduncle relatively slender and short, overreaching cornea, not reaching apex of rostrum. Article 2 with sharp distolateral spine. Antennal scale nearly reaching or slightly falling short of distal end of article 5, breadth distinctly more than twice that of article 5. Articles 4 and 5 each with small distomesial spine, that of article 4 often larger. Article 5 1.5-2.0 × longer than article 4, breadth 0.7-0.8 × height of ultimate antennular article. Flagellum of 20-22 segments barely reaching distal end of P1 merus.

Mxp: Mxp1 with bases broadly separated. Mxp3 basis with 1 distal denticle on mesial ridge. Ischium having flexor margin sharply ridged, distally rounded; crista dentata with 23-30 denticles proximally obsolescent, medially distinct, distally smaller. Merus short relative to breadth, 1.6 × longer than ischium, flattish on mesial face, sharply ridged along flexor margin, occasionally with small distolateral spine; extensor and flexor margins subparallel in distal half, flexor margin with very small tubercles or denticles distal to midlength. Carpus unarmed.

P1: 3.8-4.4 × longer than carapace, massive, moderately or sparsely setose. Ischium dorsally with basally broad, flattened, short blunt spine, ventromesially with row of short, tubercle-like processes or small spines,without distinct subterminal spine. Merus nearly as long as or slightly shorter than carapace, dorsally with distomesial spine distinct in small specimens, obsolescent or absent in large specimens, mesially with small (often distinct) spines, tubercles or granules on proximal portion, ventrally with distomesial and distolateral spines, distomesial one large and acute in small specimens. Carpus distally broadened, dorsally with 3 small blunt processes in transverse row on proximal portion, ventrally with distomesial and distolateral spines, both obtuse and small; length 1.0-1.2 × that of merus. Palm moderately depressed, 1.6-2.6 × longer than broad, 1.2-1.4 × longer than carpus; mesial margin with rounded ridge well developed in large specimens, distally diminishing in small specimens. Fingers distally curved ventrally, short relative to breadth, distally incurved, crossing when closed; opposable margin of fixed finger sinuous, that of movable finger with proximal process fitting to opposite longitudinal narrow groove on fixed finger when closed; movable finger 0.5- 0.6 × as long as palm.

P2-4: Mesio-laterally compressed, relatively broad, bearing sparse short fine setae. Meri successively shorter posteriorly (P3 merus 0.9 × length of P2 merus, P4 merus 0.8 × length of P3 merus), slightly narrower on P4 than on P2 and P3; length-breadth ratio, 3.0-3.5 on P2, 3.1-3.3 on P3, 3.2 on P4; dorsally with 3 or 4 small spines or denticles often obsolescent on P2, obsolete on P3 and P4, ventrally with small distolateral spine; P2 merus much shorter than (three-quarters) carapace, 1.1 × longer than P2 propodus; P3 merus as long as P3 propodus; P4 merus 0.8 × length of P4 propodus. Carpi subequal to or slightly shorter than length of dactyli (carpus-dactylus length ratio, 0.9 on P2 and on P3, 0.8 on P 4 in holotype), dactylus-propodus length ratio, 0.4-0.5 on P2, 0.4 on P3, 0.3-0.4 on P4; unarmed. Propodi shorter on P2 than on P3-4; flexor margin nearly straight, ending in pair of spines preceded by 4-6, 3-6, 1-5 slender spines on P2, P3 and P4, respectively. Dactyli shorter on P2 than on P3 and P4, very setose along flexor and extensor margins; length 0.4-0.5 × that of propodus on P2-4; flexor margin slightly curving, ending in slender terminal spine preceded by 8-10 loosely arranged, slightly inclined, sharp triangular spines gradually diminishing toward base of article.

Eggs. Number of eggs carried, 3-40; size, 1.16 mm × 1.00 mm - 1.25 mm × 1.48 mm.

REMARKS — Uroptychus baeomma is very close to U. elongatus n. sp. and U. modicus n. sp. Their relationships are discussed under the remarks of these species (see below).

The species also resembles U. crassipes Van Dam, 1939 in the carapace spination and the shape of the sternal plastron. However, it is differentiated from that species by the absence instead of presence of a pronounced subterminal spine on the ventromesial margin of P1 ischium; the antennal articles 4 and 5 each have a very tiny instead of strong terminal spine; the antennal scale terminates short of instead of distinctly overreaching the tip of article 5; and the P2-4 dactyli bear a slender terminal spine preceded by relatively sharp, slightly inclined, loosely arranged spines, instead of a broad penultimate spine preceded by slender, distinctly obliquely directed, closely arranged, spines.

Figures

FIGURE 28 Uroptychus baeomma n.sp.,holotype,ovigerous female 9.8 mm (MNHN-IU-2014-16310).A, carapace and anterior part of abdomen, proximal part of left P1 included,dorsal.B, same,lateral.C, anterior part of sternal plastron,with excavated sternum and basal parts of Mxp 1. D, telson. E, left antenna,ventral.F, left Mxp3, ventral.G, same, merus and carpus,lateral. Scale bars:1 mm.

FIGURE 29 Uroptychus baeomma n. sp., holotype, ovigerous female 9.8 mm (MNHN-IU-2014-16310). A, left P1, proximal part, ventral. B, same, distal part, dorsal. C, left P2, lateral. D, same, distal part, setae omitted. E, right P3, lateral. F, same, distal part, lateral. G, right P4,lateral.H, same, distal part, lateral. Scale bars: A, B, 5 mm; C-H, 1 mm.