Uroptychus exilis, 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 : 211-214

Uroptychus exilis n. sp.

Figures 94 , 95

TYPE MATERIAL — Holotype: New Caledonia, Isle of Pines. MUSORSTOM 4 Stn DW 222, 22°57.6’S, 167°33.0’E, 410- 440 m, 30.IX.1985, ♀ 3.1 mm ( MNHN-IU-2010-1793 ).

ETYMOLOGY„ From the Latin exilis (small, slender) referring to slender eyes of the species.

DISTRIBUTION„ Isle of Pines; 410- 440 m.

DESCRIPTION„ Small species. Carapace: Broader than long (0.8 × as long as broad); greatest breadth 1.7 × distance between anterolateral spines. Dorsal surface feebly convex on gastric region, without distinct groove; with sparse short setae. Lateral margins divergent posteriorly to point one-fifth from posterior end, then convergent, bearing 7 spines: first anterolateral, slightly falling short of tip of lateral orbital spine; second larger than first, situated at anterior end of anterior branchial region, equidistant between first and fourth, with accompanying small spine dorsomesial to it on left side only; third very small; fourth largest, situated at anterior end of posterior branchial margin, followed by 4 posteriorly diminishing spines, last rudimentary. Rostrum elongate triangular, with interior angle of 34°, 0.4 × as long as remaining carapace, breadth slightly less than half carapace breadth measured at posterior carapace margin; dorsal surface concave, ventral surface straight horizontal. Lateral orbital spine subequal to anterolateral spine, situated directly mesial to and moderately remote from that spine. Pterygostomian flap unarmed on surface, anteriorly angular, produced to small spine.

Sternum: Excavated sternum with convex anterior margin, smooth on surface. Sternal plastron 1.2 × as broad as long, successively broader posteriorly. Sternite 3 shallowly depressed, anterior margin excavated in broad V-shape, with small median notch. Sternite 4 having anterolateral margin relatively short, nearly straight, anteriorly ending in 2 small spines placed side by side, posterolateral margin half as long as anterolateral margin. Anterolateral margin of sternite 5 moderately convexly divergent posteriorly, 1.3 × longer than posterolateral margin of sternite 4

Abdomen: With sparse fine setae. Somite 1 smooth on surface, without ridge. Somite 2 tergite 2.4 × broader than long; pleuron posterolaterally bluntly angular, lateral margins moderately concave and divergent posteriorly. Pleuron of somite 3 tapering, with blunt lateral terminus. Telson 0.4 × as long as broad; posterior plate distinctly emarginate on posterior margin, length four-fifths that of anterior plate.

Eye: Elongate, more than 2 × longer than broad, distally narrowed, reaching distal fifth of rostrum. Cornea not dilated, less than half as long as remaining eyestalk.

Antennule and antenna: Ultimate article of antennule 2.7 × longer than high. Antennal peduncle reaching distal end of cornea. Article 2 with small but distinct distolateral spine. Antennal scale reaching end of first segment of flagellum, breadth 1.8 × that of article 5. Article 4 unarmed. Article 5 1.5 × longer than article 4, bluntly produced distomesially without distinct spine, breadth 0.7 × height of antennular ultimate article. Flagellum of 11 segments overreaching distal end of P1 merus by 2 distal segments of flagellum.

Mxp: Mxp1 with bases broadly separated. Mxp3 barely setose on lateral surface. Basis without denticles on mesial ridge. Ischium with very small denticles on crista dentata, flexor margin distally rounded. Merus 1.5 × longer than ischium, sharply ridged along distal half of flexor margin bearing small spine at distal third. Carpus unarmed.

P1: Unequal, right one slightly larger, left one possibly regenerated. Right P1 3.5 × longer than carapace; very setose, setae plumose, moderate in length. Ischium with distinct dorsal spine and small subterminal spine on ventromesial margin. Merus 0.9 × length of carapace, ventrally bearing small distomesial and distolateral spines, dorsally with distomesial spine, terminal margin in juncture with carpus with a few dorsal denticles. Carpus 0.9 × length of merus, ventrally bearing distomesial and distolateral spines. Palm 2.4 × longer than broad, unarmed, length 1.2 × that of carpus. Fingers gently curving ventrally, distally incurved, crossing when closed; opposable margins denticulate, that of movable finger with blunt

subtriangular process at proximal third, that of fixed finger sinuous, bearing low prominence slightly distal to position of opposite process on movable finger; movable finger 0.6 × length of palm.

P2-4: Moderately compressed mesio-laterally and setose. Meri successively shorter posteriorly (P3 merus 0.9 × length of P2 merus; P4 merus 0.8 × length of P3 merus), equally broad on P2-4; length-breadth ratio, 3.3 on P2, 2.9 on P3, 2.5 × on P4; P2 two-thirds as long as carapace, 1.1 × length of P2 propodus; P3 merus 0.9 × length of P3 propodus; P4 merus 0.8 × length of P4 propodus; dorsal margin unarmed, ventral margin with small distal spine on P2 and P3, unarmed on P4. Carpi subequal on P3 and P4, P3 carpus 0.9 × length of P2 carpus; length 0.5 × that of propodus on P2, 0.45 × on P3-4. Propodi successively slightly longer posteriorly; flexor margin nearly straight, ending in pair of movable spines preceded by row of 5 spines. Dactyli successively slightly longer posteriorly, moderately curving, 0.5 × length of propodi on P2 and P3, 0.6 × on P4, 1.1 × length of carpi on P2-4; flexor margin somewhat curving, with 10 loosely arranged, slightly obliquely directed spines, ultimate much more slender and shorter than penultimate, remaining spines sharp subtriangular, gradually diminishing toward base of article.

REMARKS — Uroptychus exilis most closely resembles U. posticus in the spination of the carapace lateral margin, the shape of the antenna and the spination of P2-4. Distinguishing characters of these species are outlined under the remarks of the latter species (see below). The new species also resembles U. baeomma n. sp. and U. elongatus n. sp. (see above), in the elongate eyestalks and the spination of the P2-4 dactyli. Uroptychus exilis is distinguished from these congeners by the following: the anterolateral spine of the carapace is subequal to instead of much larger than the lateral orbital spine; sternite 3 has the anterior margin excavated in a broad V-shape bearing a small median notch, instead of being shallowly excavated with 2 submedian spines flanking a subovate or narrow notch. In addition, U. exilis differs from U. baeomma in having the antennal scale distinctly overreaching, instead of at most ending in, the distal end of article 5. Uroptychus exilis also differs from U. elongatus in having the P1 ischium with a small instead of well-developed subterminal spine on the ventromesial margin.

Figures

FIGURE 94 Uroptychus exilis n. sp., holotype, female 3.1 mm (MNHN-IU-2010-1793). A, carapace and anterior part of abdomen, 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, same,lateral.H, right P1, proximal part, setae omitted, ventral.I, same,dorsal.Scale bars:1 mm.

FIGURE 95 Uroptychus exilis n. sp.,holotype,female 3.1 mm (MNHN-IU-2010-1793).A, right P2,lateral.B, same,distal part,setae omitted,lateral.C, right P3, setae omitted, lateral. D, same, distal part, setae omitted,lateral.E, right P4,setae omitted, lateral. Scale bars: 1 mm.