Uroptychus lacunatus, 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 : 253-256

Uroptychus lacunatus n. sp.

Figures 115 , 116

TYPE MATERIAL — Holotype: Vanuatu. MUSORSTOM 8 Stn CP982, 19°21.80’S, 169°26.47’E, 408-410 m, 23.IX.1994,

♂ 6.1 mm ( MNHN-IU-2014-16609 ). Paratype: Collected with holotype, 1 ov. ♀ 6.0 mm (MNHN-IU-2014-16610) .

ETYMOLOGY„ From the Latin lacunatus (hollowed out), alluding to a deeply excavated anterior margin of the sternal plastron that separates the species from U. minor n. sp.

DISTRIBUTION„ Vanuatu; 408- 410 m.

DESCRIPTION„ Medium-sized species. Carapace: 1.2-1.3 × longer than broad; greatest breadth 1.5 × distance between anterolateral spines. Dorsal surface smooth and glabrous. Gastric and cardiac regions moderately inflated, bordered by depression; no spine on surface. Lateral margins slightly divergent posteriorly; anterolateral spine well developed, distinctly overreaching much smaller lateral orbital spine; finely denticulate, short, oblique ridge discernible under high magnification on anteriormost part of branchial region. Rostrum relatively long triangular, with interior angle of 23- 25°; length 0.3-0.4 × that of remaining carapace, breadth slightly less than half carapace breadth at posterior carapace margin; dorsal surface moderately concave, ventral surface horizontal. Lateral orbital spine slightly anterior to level of anterolateral spine and separated from that spine by its basal breadth. Pterygostomian flap smooth on surface, anteriorly angular, ending in small spine.

Sternum: Excavated sternum anteriorly ending in sharp spine between bases of Mxp1, surface with small spine in center. Sternal plastron slightly longer than broad; lateral extremities divergent posteriorly. Sternite 3 strongly depressed; anterior margin strongly excavated in broad U-shape, with pair of submedian spines without notch between. Sternite 4 having anterolateral margin nearly straight, bluntly produced anteriorly; posterolateral margin somewhat more than half as long as anterolateral margin; surface with medially interrupted setiferous transverse ridge. Anterolateral margin of sternite 5 gently convexly divergent, slightly longer than posterolateral margin of sternite 4.

Abdomen: barely setose, smooth. Somite 1 convex from anterior and posterior, without distinct ridge. Somite 2 tergite 2.1 × broader than long, lateral margins slightly divergent posteriorly, posterolaterally blunt. Pleuron of somite 3 laterally blunt. Telson slightly more than half as long as broad; posterior plate 1.5 × (or slightly more) longer than anterior plate, feebly emarginate on posterior margin.

Eye: 1.6 × longer than broad, mesial and lateral margins subparallel, barely reaching apex of rostrum. Cornea not dilated, more than half as long as remaining eyestalk.

Antennule and antenna: Antennular ultimate article 1.7-1.9 × longer than high. Antennal peduncle slightly overreaching cornea but barely reaching apex of rostrum. Article 2 with small distolateral spine. Antennal scale as broad as or slightly broader than article 5, slightly overreaching midlength of article 5. Distal 2 articles unarmed; article 5 twice as long as article 4, breadth 0.4-0.5 height of antennular ultimate article. Flagellum consisting of 14 segments, barely reaching distal end of P1 merus.

Mxp: Mxp1 with bases nearly contiguous. Mxp3 glabrous on lateral surface, lacking spines on merus and carpus. Basis with 2 denticles on distal part of mesial margin. Ischium thick, crista dentata with 11-13 denticles, flexor margin distally not rounded. Merus 1.9 × longer than ischium, mesio-laterally compressed, ridged along flexor margin.

P1: Massive, 3.8-4.0 × longer than carapace, with small sharp distodorsal spine on ischium, unarmed elsewhere; ventral surface of ischium and carpus with tubercles somewhat more numerous in female paratype than in male holotype; dorsal surfaces smooth, merus and carpus barely setose. Merus slightly longer (holotype) or slightly shorter (paratype) than carapace. Carpus 1.2 × longer than merus. Palm distally setose (bearing simple setae), 2.2-2.3 × longer than broad, 0.9 × as long as carpus; lateral and mesial margins slightly convex. Fingers broad relative to length, distally incurved,

crossing when closed; opposable margins minutely denticulate, nearly straight along entire length of fixed finger, with prominent but low proximal process on movable finger; movable finger about half as long as palm.

P2-4: Moderately compressed mesio-laterally, broad relative to length. Meri successively shorter posteriorly (P3 merus 0.8 × length of P2 merus, P4 merus 0.7-0.8 × length of P3 merus), successively narrower posteriorly; length-breadth ratio, 4.0-4.5 on P2, 3.6-3.9 on P3, 3.4-3.7 on P4; dorsal margin not cristiform but rounded and unarmed; P2 merus 0.9 × length of carapace, 1.3-1.5 × length of P2 propodus; P3 merus 1.3 × length of P3 propodus; P4 merus 0.9 × length of P4 propodus. Carpi successively shorter posteriorly; carpus-propodus length ratio, 0.6 on P2, 0.5-0.6 on P3, 0.5 on P4. Propodi longest on P2 or subequal on P2 and P3, shortest on P4; flexor margin straight, ending in pair of spines located near juncture with dactylus, preceded by 8-10 movable spines on P2, 7-8 spines on P3, 6-7 spines on P4. Dactyli moderately curving at proximal third; dactylus-carpus length ratio, 0.7 on P2, 0.7-0.8 on P3, 1.0 on P4; dactylus-propodus length ratio, 0.4 on P2, 0.4-0.5 on P3, 0.5 on P4; flexor margin with 9-12 sharp triangular, loosely arranged, proximally diminishing and somewhat inclined spines obscured by setae, ultimate subequal to penultimate.

Eggs. 13 eggs, 1.04 mm × 1.10 mm - 1.18 mm × 1.39 mm.

REMARKS — The elongate carapace and relatively massive P1 as displayed by the species are possessed by U. minor n. sp. Also, U. lacunatus resembles U. stenorhynchus n. sp. in having the elongate carapace and the anteriorly angular pterygostomian flap, in the shape of sternum 3, and in the spination of the P2-4 dactyli. Their relationships are discussed under the remarks of those species (see below).

Figures

FIGURE 115 Uroptychuslacunatus n.sp.,A-C, E-H,holotype,male 6.1 mm (MNHN-IU-2014-16609);D,paratype,ovigerous female (MNHN-IU-2014-16610). A, carapace and anterior part of abdomen,proximal part of right P1 included,dorsal.B, same,lateral.C, sternal plastron,with excavated sternum and basal parts of Mxp1.D, telson.E, left antenna,ventral.F, right Mxp3,setae omitted,ventral.G, left P3,setae omitted from distal articles, lateral.H, right P1, dorsal. Scale bars: 1 mm.

FIGURE 116 Uroptychus lacunatus n. sp.,holotype,male 6.1 mm (MNHN-IU-2014-16609).A, right P2,lateral.B, same,setae omitted,lateral.C, same, distal part, lateral. D, right P3,lateral.E, right P4, lateral. Scale bars:1 mm.