Uroptychus mesodme, 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 : 308-311

Uroptychus mesodme n. sp.

Figures 145 , 146

TYPE MATERIAL — Holotype: Fiji Islands. BORDAU 1 Stn CP 1461, 18°09’S, 178°48’W, 560 m, 6.III.1999, 1 ♂ 3.9 mm ( MNHN-IU-2014-16729 ).

ETYMOLOGY„ From the Greek mesodme (something between), alluding to a pair of small spines between two larger epigastric spines.

DISTRIBUTION„ Fiji Islands, 560 m.

DESCRIPTION — Carapace: Broader than long (0.8 × as long as broad); greatest breadth 1.6 × distance between anterolateral spines. Dorsal surface smooth, gastric region smoothly sloping down to rostrum, posterior portion (cardiac and intestinal regions) somewhat convex; somewhat ridged along posterior fifth of lateral margin; epigastric region with 2 pairs of spines, mesial pair small, situated behind eyes, lateral pair well developed, somewhat lateral to midpoint of upper orbital margin. Lateral margins constricted at anterior third; anterior part (anterior to constrictions) gently divergent posteriorly, with 3 spines, first anterolateral, strong, directed straight forward, reaching proximal part of cornea, second small, situated at level of first, directed anteriorly, third strong, somewhat dorsal to level of second, directed anterolaterally; posterior part (posterior to constrictions) well convex, with 5 short, posteriorly diminishing spines (anteriormost preceded by small spine on left side; left second small). Rostrum narrow triangular, distally curving dorsally, with interior angle of 21°; length 1.2 × breadth, 0.4 × that of remaining carapace; dorsal surface moderately concave; breadth less than half carapace breadth at posterior carapace margin. Lateral orbital spine small, situated somewhat anterior to level of anterolateral spine. Pterygostomian flap anteriorly angular, produced to strong spine, surface with 2 (right) or 4 (left) spines on anterior part; height of posterior portion 0.5 × that of anterior portion.

Sternum: Excavated sternum with sharp ridge in midline leading onto anterior margin produced triangularly between bases of Mxp1. Sternal plastron 1.5 × broader than long; lateral extremities convexly divergent behind sternite 4, sternite 7 slightly narrower than sternite 6. Sternite 3 shallowly depressed; anterior margin moderately concave, with V-shaped median notch without flanking spine. Sternite 4 short relative to breadth; anterolateral margin slightly convex, anteriorly rounded, length 1.6 × that of posterolateral margin. Sternite 5 with convex anterolateral margin as long as posterolateral margin of sternite 4.

Abdomen: Somites short relative to breadth. Somite 1 well convex from anterior to posterior. Somite 2 tergite 3.0 × broader than long; pleuron moderately produced posterolaterally, ending in blunt margin. Pleuron of somite 3 laterally tapering to blunt end, those of somites 4-5 laterally rounded. Telson 0.5 × as long as broad; posterior plate 1.3 × longer anterior plate, posterior margin slightly concave.

Eye: Elongate, 2.0 × longer than broad, barely reaching apex of rostrum, slightly broadened proximally. Cornea 0.6 × length of remaining eyestalk.

Antennule and antenna: Ultimate article of antennular peduncle 2.9 × longer than high. Antennal article 2 with strong distolateral spine. Antennal scale proportionately broad, 1.3 × broader than article 5, ending in point two-thirds of length of article 5. Article 4 with bluntly produced distomesial spine. Article 5 unarmed, length 1.3 × that of article 4, breadth 0.5 × height of ultimate article of antennule. Flagellum of 14 segments reaching distal end of P1 merus.

Mxp: Mxp1 with bases broadly separated. Mxp3 basis without denticle on mesial ridge. Ischium having flexor margin distally rounded, crista dentata with denticles nearly obsolete, only visible under high magnification. Merus twice as long as ischium, mesial face flattish; flexor margin roundly ridged on proximal half, sharply ridged on distal half, bearing 1 blunt very short spine at distal third; lateral face with short blunt distal spine. Carpus unarmed.

P1: 7.2 × longer than carapace, smooth and barely setose except for fingers. Ischium with strong dorsal spine accompanying small spine proximally; ventromesial margin with subterminal spine very short and blunt, not reaching distal end of ischium, proximally with a few obsolescent protuberances. Merus with 2 rows each of short blunt spines (dorsomesial row of 2 spines, ventromesial row of 5 spines), ventral distomesial spine blunt and short; length 1.4 × that of carapace. Carpus 1.5 × length of merus, mesial margin with terminal spine followed proximally by 3 rudimentary spines. Palm unarmed, depressed, twothirds as high as broad, 4.5 × longer than broad, lateral and mesial margins subparallel. Fingers relatively slender distally, sparingly setose, moderately gaping in proximal two-thirds, not incurved distally; fixed finger directed slightly laterally, with low eminence at distal third; movable finger 0.4 × as long as palm, opposable margin with prominent median process (distal margin of process perpendicular to opposable margin); no longitudinal groove on ventromesial face of fixed finger.

P2-4: Relatively slender, well compressed mesio-laterally, with sparse simple setae, more setose on propodi and dactyli. Ischia with 2 short dorsal spines. Meri subequal in length on P2 and P3, shortest on P4 (P4 merus 0.6 × length of P3 merus); subequally broad on P2 and P3, slightly narrower on P4; dorsal margins unarmed; length-breadth ratio, 5.0 on P2 and P3, 3.2 on P4; P2 merus as long as carapace, 1.1 × longer than P2 propodus; P3 merus 1.1 × length of P3 propodus, P4 merus 0.6 × length of P4 propodus. Carpi successively shorter posteriorly, 0.5 × length of propodus on P2, 0.4 × on P3 and P4. Propodi subequal in length on P2 and P3, shortest on P4; flexor margin slightly concave in lateral view, with pair of slender terminal spines only. Dactyli subequal in length on P2-4; dactylus-carpus length ratio, 1.0 on P2, 1.2 on P3, 1.7 on P4; dactylus-propodus length ratio, 0.5 on P2 and P3, 0.6 on P4; flexor margin slightly curving in lateral view, with 9 sharp spines proximally diminishing, loosely arranged and nearly perpendicular to margin, ultimate spine more slender than penultimate.

REMARKS — As mentioned above under the account of U. clarki n. sp., U. mesodme resembles U. paraplesius n. sp. and U. trispinatus n. sp., sharing the carapace lateral margin with a group of 3 spines on the anterior part remotely separated from a group of 3-5 spines on the posterior part, the antennal scale overreaching the midlength of article 5, and article 4 bearing a distomesial spine. Characters distinguishing U. mesodme from U. paraplesius and U. trispinatus are discussed under the latter two species (see below).

Figures

FIGURE 145 Uroptychus mesodme n. sp.,holotype, male 3.9 mm (MNHN-IU-2014-16729).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, right pleura of abdominal somites 2-5,dorsolateral. E, telson.F, left antenna,ventral.G, right Mxp3,crista dentata,ventral.H, left Mxp3, setae omitted, lateral. Scale bars: 1 mm.

FIGURE 146 Uroptychus mesodme n. sp.,holotype,male holotype 3.9 mm (MNHN-IU-2014-16729).A, right P1, proximal part,lateral. B, same,ventral.C, same, distal three articles,dorsal.D, right P2,lateral.E, same,distal part,setae omitted,lateral.F, right P3,setae omitted,lateral.G, right P4,setae omitted, lateral.Scale bars: 1 mm.