Uroptychus dissitus, 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 : 182-185

Uroptychus dissitus n. sp.

Figures 78 , 79

TYPE MATERIAL — Holotype: Vanuatu. MUSORSTOM 8 Stn DW 1060, 16°14’S, 167°21’E, 394- 375 m, 2.X.1994, ♂ 2.4 mm ( MNHN-IU-2014-16395 ).

ETYMOLOGY„ From the Latin dissitus (distant), alluding to the anterior second of the carapace lateral marginal spines that is remotely separated from the first anterolateral spine.

DISTRIBUTION„ Vanuatu; 397- 375 m.

DESCRIPTION„ Carapace: Slightly broader than long (0.9 × as long as broad); greatest breadth 1.4 × distance between anterolateral spines. Dorsal surface smooth, bearing scattered short setae, nearly horizontal from anterior to posterior, with feebly depression between gastric and cardiac regions. Lateral margins slightly convex and slightly divergent posteriorly, bearing 6 spines: first spine anterolateral, reaching tip of smaller lateral orbital spine, and close to that spine; second to sixth situated on branchial margin, posteriorly diminishing, second nearly as large as first, placed at anterior end of branchial margin and remotely equidistant between first and third; last followed by 1 or 2 tubercles. Rostrum sharp triangular, with interior angle of 22°; dorsal surface moderately concave; length about half length of carapace, breadth half carapace breadth measured at posterior carapace margin. Pterygostomian flap nearly smooth but scattered very tiny tubercles supporting short setae on surface, anterior margin angular, produced to small spine.

Sternum: Excavated sternum anteriorly triangular, bearing ridge in midline. Sternal plastron about as long as broad; lateral extremities subparallel between sternites 4-7. Sternite 3 shallowly depressed, anterior margin weakly concave, with narrow U-shaped median sinus without flanking spine, anterolaterally angular. Sternite 4 having anterolateral margin nearly straight, anteriorly bidentate; posterolateral margin slightly shorter than anterolateral margin. Anterolateral margin of sternite 5 convex anteriorly, length 0.8 × that of posterolateral margin of sternite 4.

Abdomen: With very sparse short setae. Somite 1 moderately convex from anterior to posterior. Somite 2 tergite 2.8 × broader than long; pleuron anterolaterally blunt angular, posterolaterally rounded, lateral margin somewhat concave, slightly divergent posteriorly. Pleuron of somite 3 bluntly angular on posterolateral terminus. Telson slightly less than half as long as broad; posterior plate with convex posterior margin, length 1.2 × that of anterior plate.

Eye: Slightly falling short of rostral tip, 1.6 × longer than broad, lateral and mesial margins slightly convex. Cornea not dilated, more than half as long as remaining eyestalk.

Antennule and antenna: Ultimate antennular article 2.9 × longer than high. Antennal peduncle overreaching eye, nearly reaching rostral tip. Article 2 with acute short distolateral spine. Antennal scale slightly overreaching article 5; breadth about 1.7 × that of article 5. Articles 4 and 5 each with distomesial spine. Article 5 1.3 × longer than article 4, breadth slightly less than half height of antennular ultimate article. Flagellum consisting of 10-11 segments, barely reaching distal end of P1 merus.

Mxp: Mxp1 with bases close to each other. Mxp3 basis smooth, without denticles on mesial ridge. Ischium having flexor margin distally rounded; crista dentata with obsolescent denticles. Merus 2.0 × longer than ischium, broad relative to length, flattish, and concave on mesial face; flexor margin sharply cristate and convex on distal third, bearing a few obsolete denticles. Small but distinct distolateral spine on each of merus and carpus.

P1: 5.5 × longer than carapace, smooth, moderately setose but glabrous on ventral surface, setae arising from short transverse or scale-like granulate ridges. Ischium with long, sharp dorsal spine, ventromesially with strong subterminal spine. Merus 1.2 × length of carapace, dorsally with a few distal spines near juncture with carpus, and row of small spines along dorsomesial margin, mesially with 3-4 strong, proximally diminishing spines on proximal half of length; ventrally with sparse granules supporting setae, and small distolateral and strong distomesial spines. Carpus also with 2 distoventral (mesial and lateral) spines, 3 small distodorsal spines, a few tubercles distal to dorsal juncture with merus; length slightly more than that of merus. Palm unarmed, somewhat massive but moderately depressed, somewhat broader distally, 2.7- 2.8 × longer than broad, 1.2 × longer than carpus. Fingers gaping, distally incurved, crossing when closed; movable finger half as long as palm, opposable margin angular at distal quarter, with process of moderate size proximal to midlength, opposing margin of fixed finger somewhat sinuous.

P2-4: Setose like P1, moderately compressed mesio-laterally. Meri dorsally unarmed, ventrally with distolateral spine, successively shorter posteriorly (P3 merus 0.95 × length of P2 merus, P4 merus 0.8 × length of P3 merus), subequally broad on P2-4; length-breadth ratio, 4.6 on P2, 3.7 on P3, 3.0 on P4; P2 merus slightly shorter than carapace, 1.2 × longer than P2 propodus; P3 merus as long as P3 propodus; P4 merus 0.8 × length of P4 propodus. Carpi subequal; each carpus less than half as long as propodus (carpus-propodus length ratio, 0.45 on P2, 0.40 on P3, 0.37 on P4), distinctly shorter than dactylus. Propodi shortest on P2, subequal on P3 and P4; flexor margin ending in pair of spines located at juncture with dactylus, preceded by 4 or 5 spines on P2 and P3, 2 or 3 on P4. Dactyli subequal on P3 and P4 and shorter on P2; dactylus-propodus length ratio, 0.6 on P2, 0.5 on P3 and P4; 1.4 × longer than carpi on P2-4 (1.2 × longer on left P2); flexor margin nearly straight, with 13-15 obliquely directed, closely arranged spines obscured by setae, penultimate spine more than twice breadth of other spines and distally blunt, remainder slender, distal spines nearly contiguous to one another.

REMARKS — The carapace shape and the spination of the P2-4 dactyli of the species are very similar to those of U. spinu-

lus n. sp. Their relationships are discussed under that species (see below).

Figures

FIGURE 78 Uroptychus dissitus n. sp., holotype, male 2.4 mm (MNHN-IU-2014-16395). A, carapace and anterior part of abdomen, setae omitted on right half,proximal part of right P1 included,dorsal. B, same, setae omitted,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.Scale bars:1 mm.

FIGURE 79 Uroptychus dissitus n. sp., holotype, male 2.4 mm (MNHN-IU-2014-16395). A, left P1, proximal part, ventral. B, same, distal part, dorsal. C, left P2, lateral.D, same,distal part,setae omitted, lateral. E, right P3, setae omitted,lateral.F, right P4,lateral. Scale bars:1 mm.