Uroptychus septimus, 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 : 470-473

Uroptychus septimus n. sp.

Figures 235 , 236

TYPE MATERIAL — Holotype: Wallis and Futuna Islands. MUSORSTOM 7 Stn DW 523, 13°12’S, 176°16’W, 455-515 m, with corals of Chrysogorgiidae (Calcaxonia) , 13.V.1992, ov. ♀ 7.1 mm ( MNHN-IU-2014-16947 ).

ETYMOLOGY„ From the Latin septimus (seventh), alluding to the seventh cruise of MUSORSTOM, by which the species was taken.

DISTRIBUTION„ Wallis and Futuna Islands (SW Pacific); 455- 515 m.

DESCRIPTION„ Medium-sized species. Carapace: Nearly as long as broad; greatest breadth 1.5 × distance between anterolateral spines. Dorsal surface smooth and glabrous, nearly horizontal in profile, smoothly sloping down anteriorly to rostrum. Lateral margins slightly convex; anterolateral spine small, located somewhat posterior to level of lateral orbital angle, and not overreaching that spine; tubercle-like small spine at point one-fifth from anterior end (anterior end of branchial margin), followed by granulation; no ridge along posterior portion. Rostrum narrow triangular, with interior angle of 23°, slightly overreaching eyes; dorsal surface somewhat concave; ventral surface straight horizontal; lateral margins somewhat concave; length less than half that of remaining carapace, breadth half carapace breadth at posterior carapace margin. Lateral limit of orbit acuminate, lacking distinct spine. Pterygostomian flap with somewhat roundish anterior margin lacking distinct spine; surface smooth.

Sternum: Excavated sternum with anterior margin with small median spine between bases of Mxp1; surface with small spine in center. Sternal plastron 1.1 × broader than long, lateral extremities straight divergent posteriorly. Sternite 3 depressed well, anterior margin strongly excavated in broad V-shape, with pair of sharp submedian spines separated by V-shaped notch, anterolateral angle rounded. Sternite 4 having convex anterolateral margin anteriorly ending in spine nearly as large as submedian spines of sternite 3, followed by posteriorly diminishing denticles; posterolateral margin about half as long as anterolateral margin. Sternite 5 having anterolateral margin strongly convex, 1.3 × longer than posterolateral margin of sternite 4.

Abdomen: Smooth and glabrous, with relatively long somites. Somite 1 feebly convex from anterior to posterior. Somite 2 tergite 2.1 × broader than long; pleuron posterolaterally blunt; lateral margins concavely strongly divergent posteriorly. Pleuron of somite 3 with blunt lateral terminus. Telson two-thirds as long as broad; posterior plate distinctly emarginate, length 1.8 × that of anterior plate.

Eye: Slightly falling short of apex of rostrum, about twice as long as broad, lateral and mesial margins somewhat concave. Cornea somewhat inflated, length much more than half that of remaining eyestalk. Antennule and antenna: Ultimate article of antennular peduncle 2.5 × longer than high. Antennal peduncle relatively slender, reaching distal end of cornea. Article 2 distolaterally acuminate, lacking distinct spine. Antennal scale 1.5 × broader than article 5, tapering, slightly falling short of distal end of article 5 and distal end of eye. Article 4 unarmed. Article 5 with small distomesial spine; length 2.7 × that of article 4, breadth half height of ultimate article of antennule. Flagellum consisting of 17 or 20 segments, nearly reaching distal margin of P1 merus.

Mxp: Mxp1 with bases very close to each other. Mxp3 scarcely setose laterally. Basis with 1 distal denticle proximally followed by 1 or 2 obsolescent denticles. Ischium with 25-26 denticles on crista dentata, flexor margin distally not rounded. Merus 1.9 × longer than ischium, unarmed, not well compressed mesio-laterally, ridged along smoothly convex flexor margin. Carpus with obsolescent distolateral spine.

P1: Moderately massive, 5.2 × longer than carapace; sparsely setose except for fingers, setae relatively short. Ischium dorsally with broad short spine, ventromesially feebly denticulate, without subterminal spine. Merus 1.3 × longer than carapace, unarmed except for very small distomesial and distolateral spines on ventral surface, ventromesially feebly granular. Carpus 1.2 × longer than merus. Palm smooth dorsally, rounded on mesial margin, 2.8 × longer than broad, 0.9 × length of carpus. Fingers slightly gaping, distally crossing when closed; fixed finger with low median eminence on opposable margin; movable finger about half as long as palm, opposable margin with disto-proximally broad, bluntly bidentate proximal process.

P2-4: Slender, with sparse long setae. Meri moderately compressed mesio-laterally, dorsally unarmed, ventrolaterally ending in small spine; successively diminishing posteriorly (P3 merus 0.9 × length of P2 merus, P4 merus 0.9 × length of P3 merus), subequally broad on P2 and P3, somewhat narrower on P4 (P4 merus 0.9 × breadth of P3 merus); lengthbreadth ratio, 6.2 on P2, 5.6 on P3 and P4; P2 merus as long as carapace, 1.5 × longer than P2 propodus; P3 merus 1.2 × length of P3 propodus; P4 merus as long as P4 propodus. Carpi subequal in length on P2 and P3, shortest on P4; much longer than dactyli (carpus-dactylus length ratio, 2.0 on P2, 1.7 on P3, 1.5 on P4); carpus-propodus length ratio, 0.7 on P2, 0.6 on P3, 0.5 on P4; extensor margin with small distal spine at most on P2. Propodi longest on P3, shortest on P2; flexor margin nearly straight, with pair of distal spines slightly distant from juncture with dactylus and preceded by row of spines (8 or 11 on P2, 8 on P3, 6 or 7 on P4) nearly along entire length on P2, slightly more distally on P3 and P4, distalmost of these unpaired spines equidistant between distal second and terminal pair. Dactyli relatively slender, strongly curving at proximal third, ending in prominent spine preceded by 7-8 smaller flexor marginal spines moderately inclined, loosely arranged and diminishing toward base of article; dactylus-carpus length ratio, 0.5 on P2, 0.6 on P3, 0.7 on P4; dactyluspropodus length ratio, 0.35-0.36 on P2, 0.35 on P3, 0.36 on P4.

Eggs. Number of eggs carried, 7; diameter, 1.4 mm.

REMARKS„ The new species resembles U. comptus Baba, 1988 , U. empheres Ahyong & Poore, 2004 , U. pollostadelphus n. sp. and U. sagamiae Baba, 2005 in the carapace shape, in having the pterygostomian flap roundish on the anterior margin, and in having the P2-4 dactyli with the ultimate of the flexor spines strongest. Uroptychus comptus and U. empheres can be separated from the other species including U. septimus by having no epigastric spines. They also differ from U. septimus in having no spine on the antennal article 5 and in having a ventrally granulose P1 merus. Uroptychus septimus is differentiated from U. pollostadelphus by the P2-4 meri that are successively shorter posteriorly, with the P4 merus 0.9 times as long as the P3 merus (in U. pollostadelphus , the P2 merus is as long as the P3 merus and the P4 merus is much shorter, 0.6 times the length of the P3 merus); the antennal article 2 is distolaterally acuminate instead of bearing a distinct spine, and the article 5 bears a distinct distomesial spine instead of being unarmed. Uroptychus septimus differs from U. sagamiae Baba, 2005 in having the antennal article 2 distolaterally acuminate instead of bearing a distolateral spine; the antennal scale is barely reaching instead of overreaching the distal end of the article 5; the P1 palm is smooth instead of denticulate on the ventral surface; the P2 merus is as long as instead of much shorter than the carapace and 1.5 times longer than instead of as long as the P2 propodus; and the P2 carpus is longer, being 0.7 instead of 0.5 times the length of the P2 propodus.

Figures

FIGURE 235 Uroptychus septimus n. sp., holotype, ovigerous female 7.1 mm (MNHN-IU-2014-16947). A, carapace and anterior part of abdomen, proximal part of left P1 included, dorsal. B, same, lateral.C, right eye and part of rostrum, dorsal. D, sternal plastron, with excavated sternum and basal parts of Mxp1.E, telson.F, left antenna,ventral.G, right Mxp3,setae omitted, ventral.H, same,lateral.I, left P1,dorsal. Scale bars:A, B, I, 5 mm; C-H,1 mm.

FIGURE 236 Uroptychus septimus n. sp.,holotype,ovigerous female 7.1 mm (MNHN-IU-2014-16947).A, right P2,lateral.B, same,distal part,setae omitted, lateral.C, left P3, setae omitted,lateral.D, right P4, setae omitted, lateral.Scale bars: 1 mm.