Uroptychus spinulus Baba 2018, n. sp.

Uroptychus spinulus n. sp.

Figures 248, 249

TYPE MATERIAL — Holotype: Vanuatu. MUSORSTOM 8 Stn DW 1030, 17°51.80’S, 168°30.44’E, 180-190 m, 29.IX.1994, ♂ 3.5 mm (MNHN-IU-2014-16964). Paratypes: Vanuatu. MUSORSTOM 8 Stn DW 1030, collected with holotype, 1 ♀ 3.8 mm (MNHN-IU-2014-16965). – Stn CP1084, 15°50.29’S, 167°17.48’E, 207-280 m, 5.X.1994: 1 ♂ 3.8 mm, 2 ov. ♀ 3.3, 3.5 mm (MNHN-IU-2014-16966).

ETYMOLOGY„ From the Latin spinulus (dim. of spina, small spine), referring to small spines (two in number) on the dorsal proximal margin of P2 merus, a character to help separate the species from related species.

DISTRIBUTION„ Vanuatu; 180- 280 m.

SIZE„ Males, 3.5-3.8 mm; females, 3.3-3.8 mm; ovigerous females from 3.3 mm.

DESCRIPTION„ Small species. Carapace: Slightly broader than long (0.9 × as long as broad); greatest breadth 1.6 × distance between anterolateral spines. Dorsal surface smooth and nearly glabrous; cardiac region very weakly convex; gastric region almost horizontal, preceded by depressed rostrum. Lateral margins slightly convexly divergent posteriorly, bearing 6 spines; first anterolateral spine, overreaching tiny lateral orbital spine and situated slightly posterior to level of and separated from that spine at most by its basal breadth; second remote from first, equidistant between first and third; fifth located at midlength of posterior branchial margin, sixth very small or absent, occasionally followed by a few tubercle-like processes. Rostrum sharp triangular, with interior angle of about 30°; dorsal surface straight horizontal and concave, ventral surface directed dorsally; length about half that of carapace, breadth half carapace breadth at posterior carapace margin. Pterygostomian flap with roundish anterior margin bearing small spine; surface smooth, bearing spine or tubercle on anterior portion.

Sternum: Excavated sternum with sharp ridge in midline, anterior margin triangular. Sternal plastron slightly broader than long, lateral extremities divergent posteriorly on sternites 4-7. Sternite 3 moderately depressed, anterior margin gently concave with U-shaped median notch without flanking spine, anterolateral corner angular. Sternite 4 having anterolateral margin entire and slightly concave, anterior end angular, posterolateral margin slightly shorter than anterolateral margin.

Anterolateral margin of sternite 5 anteriorly rounded, divergent posteriorly, length 0.7 × that of posterolateral margin of sternite 4.

Abdomen: Dorsal surface smooth with very sparse short setae. Somite 1 with somewhat elevated transverse ridge. Somite 2 tergite 2.6-2.8 × broader than long; pleuron posterolaterally blunt angular, lateral margin moderately concave and divergent posteriorly. Pleuron of somite 3 laterally blunt. Telson slightly less than half as long as broad; posterior plate slightly longer than anterior plate, feebly concave on posterior margin.

Eye: Elongate, 2 × as long as broad, overreaching midlength of rostrum, somewhat narrowed distally. Cornea about half as long as remaining eyestalk.

Antennule and antenna: Antennular ultimate article about 3 × longer than high. Antennal peduncle overreaching cornea, slightly falling short of rostral tip. Article 2 with small or obsolescent distolateral spine. Antennal scale 2 × as broad as article 5, sharply tapering, slightly overreaching midlength of article 5. Article 4 with distomesial spine. Article 5 with very small or obsolescent distomesial spine, length 1.5-1.7 × that of article 4, breadth less than half height of ultimate article of antennular peduncle. Flagellum of 11-14 segments not reaching distal end of P1 merus.

Mxp: Mxp1 with bases close to each other or nearly contiguous. Mxp3 scarcely setose on lateral surface. Basis without denticles on mesial ridge. Ischium with flexor margin distally rounded; crista dentata almost entire, without denticles. Merus twice as long as ischium, flexor margin moderately ridged, bearing 2 very small spines distal to point one-third from distal end; distolateral spine distinct. Carpus also with distolateral spine.

P1: More slender in females than in males, 5.3-5.8 × longer than carapace, smooth, bearing long setae on fingers, sparsely setose elsewhere. Ischium dorsally with long spine, ventromesially with well-developed subterminal spine. Merus 1.1-1.2 × longer than carapace, dorsally with very small distomesial spine, ventrally with distomesial and distolateral spines. Carpus with mesial and lateral distoventral spines and 2 tubercle-like processes distal to dorsal juncture with merus, length 1.3 × that of merus. Palm massive in males, 3.0-3.1 × (males), 4.6-4.9 × (females) longer than broad, 2.2-2.4 × (males), 2.8-2.9 × (females) longer than movable finger, 1.1-1.2 × longer than carpus. Fingers distally ending in incurved small spine, not spooned; in females, opposable margin of movable finger with strong median process distal to proximal process of fixed finger; in males, fingers gaping, opposable margins fitting to each other (or slightly crossing) in distal third of length when closed, fixed finger lacking proximal process, movable finger with prominent process on midlength of gaping margin; movable finger 0.3-0.4 × length of palm.

P2-4: With fine plumose setae, denser on dactyli. Ischium with 2 small distal spines on extensor margin. Meri successively diminishing posteriorly (P3 merus 0.7-0.8 × length of P2 merus, P4 merus 0.7-0.8 × length of P3 merus); breadths subequal on P2-4; length-breadth ratio, 6.1-7.3 on P2, 4.5-5.0 on P3, 3.7-3.8 on P4; dorsal margin with 1 or 2 (usually 2) spines distinct near proximal end on P2, occasionally obsolescent on P3, vestigial or absent on P4; row of tubercle-like small spines along entire ventromesial margin on P2 only, and distinct spine at distal end of ventrolateral margin (obsolescent on P3 and P4); P2 merus 1.2 × longer than carapace, 1.5-1.7 × longer than P2 propodus; P3 merus 0.9 × length of P3 propodus; P4 merus 0.9 × length of P4 propodus. Carpi successively slightly shorter posteriorly or subequal on P3-4; carpus-propodus length ratio, 0.4-0.5 on P2, 0.4 on P3, 0.3-0.4 on P4; extensor margin with small distal spine distinct or obsolescent on P2, absent on P3 and P4. Propodi subequal on P2 and P4, longest on P3, or subequal on P2-4; flexor margin straight, with pair of terminal spines preceded by 14-17 slender movable spines in zigzag arrangement along entire length. Dactyli as long as carpi on P2, 1.3 × longer on P3, 1.5 × longer on P4; dactylus-propodus length ratio, 0.4 on P2, 0.5 on P3, 0.5-0.6 on P4; flexor margin slightly curving, with 12-14 obliquely directed spines closely arranged and obscured by dense setae, ultimate spine slender, penultimate 2 × broader than antepenultimate, remaining spines slender, close to one another but not contiguous.

Eggs. Number of eggs carried, 6; size, 0.93 mm × 0.98 mm - 0.93 mm × 1.19 mm.

REMARKS — The arrangements of spines on the carapace and P2-4 dactyli are very much like those of U. dissitus n. sp. (see above). Uroptychus spinulus is distinguished from U. dissitus by the following: the pterygostomian flap is anteriorly roundish instead of angular, although ending in a small spine in both species; the antennal scale slightly overreaches the midlength of article 5, not reaching the end of that article, instead of slightly overreaching the distal end of article 5; the P1 merus is mesially smooth and unarmed instead of bearing strong spines; the P2 merus bears 1 or 2 (usually 2) dorsal spines on the proximal portion instead of being unarmed; and the P2-4 propodi bear a row of 14-17 flexor spines, other than the terminal pair, along the entire length, instead of at most 5 spines on the distal half.