Uroptychus paraplesius, 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 : 376-381

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Uroptychus paraplesius

n. sp.

Uroptychus paraplesius n. sp.

Figures 185-188 View FIGURE 185 View FIGURE 186 View FIGURE 187 View FIGURE 188

TYPE MATERIAL — Holotype: Indonesia, Kai Islands. KARUBAR Stn CP16, 5°17’S, 132°50’E, 315-349 m, 24.X.1991, ♂ 5.3 mm ( MNHN-IU-2014-16837 ) GoogleMaps . Paratype: Collected with holotype, 1 ov. ♀ 6.0 mm (MNHN-IU-2014-16838) . New Caledonia, Isle of Pines. BIOCAL Stn CP52, 23°06’S, 167°47’E, 600- 540 m, 31.VIII.1985, with rhizocephalan parasite, 1 ♂ 3.2 mm (MNHN-IU-2013-8574).

DISTRIBUTION„ Kai Islands ( Indonesia) and Isle of Pines; 315- 600 m.

ETYMOLOGY„ From the Greek paraplesios (somewhat similar), alluding to the morphological characteristics of the species, which are somewhat similar to those of U. trispinatus n. sp. described in this paper.

DESCRIPTION„ Small species. Carapace: Broader than long (0.8-0.9 × as long as broad); greatest breadth 1.8 × distance between anterolateral spines. Dorsal surface smooth, moderately convex from anterior to posterior, with shallow depression between gastric and cardiac regions; epigastric region with pair of small spines. Lateral margins with constriction at anterior third; anterior part (anterior to constrictions) divergent posteriorly, with 3 prominent spines, all directed anteriorly and somewhat laterally, first anterolateral, overreaching base of antennal scale, second slightly smaller than first, situated at same level as first, third strongest, distinctly dorsal to level of first and second; posterior part (posterior to constrictions) gently convex, with 4 or 5 sharp, posteriorly diminishing spines, all directed anterolaterally like those on anterior part, last spine followed by feeble ridge leading to posterior end. Rostrum narrow triangular, with interior angle of 21-25°, straight horizontal, dorsal surface concave; length 0.4 × that of remaining carapace, breadth much less than half carapace breadth at posterior carapace margin. Lateral orbital spine small, slightly anterior to level of anterolateral spine. Pterygostomian flap anteriorly angular, produced to strong spine, followed by a few well-developed spines on anterior part; height of posterior portion 0.5 × that of anterior portion.

Sternum: Excavated sternum sharply ridged in midline on surface, anterior margin produced triangularly between bases of Mxp1. Sternal plastron 1.3-1.5 × broader than long, lateral extremities convexly divergent behind sternite 4, sternites 6 and 7 subequal in breadth. Sternite 3 shallowly depressed; anterior margin excavated in shallow V-shape, with V-shaped median notch. Sternite 4 having anterolateral margin feebly convex, anteriorly blunt angular, 1.7-1.9 × longer than posterolateral margin. Sternite 5 with medially convex anterolateral margin longer than posterolateral margin of sternite 4.

Abdomen: Somite 1 convex from anterior to posterior. Somite 2 tergite 3.3 × longer than broad, pleuron posterolaterally moderately produced, somewhat more produced in female. Pleuron of somite 3 blunt on lateral terminus, those of somites 4 and 5 laterally rounded. Telson about half as long as broad; posterior plate 1.7 × longer than anterior plate, posterior margin feebly emarginate.

Eye: Elongate, 2.0-2.1 × longer than broad, overreaching midlength of, not overreaching point distal third of rostrum, distally narrowed. Cornea feebly dilated, about half as long as remaining eyestalk.

Antennule and antenna: Ultimate article of antennular peduncle 2.4-2.9 × longer than high. Antennal peduncle reaching apex of rostrum. Article 2 with strong distolateral spine. Antennal scale 1.5 × as broad as article 5, reaching end of first segment of flagellum. Article 4 with strong distomesial spine accompanying smaller spine at its ventromesial base. Article 5 with short distomesial spine, length 1.4-1.5 × that of article 4, breadth 0.5-0.6 × height of ultimate article of antennule. Flagellum of 9 segments not reaching distal end of P 1 merus.

Mxp: Mxp1 with bases moderately separated. Mxp3 basis with 1 distal denticle on mesial ridge. Ischium having flexor margin distally rounded, crista dentata with 20-23 distally diminishing denticles. Merus twice as long as ischium; mesial face flattish; flexor margin roundly ridged on proximal half, sharply ridged on distal half, produced around distal third bearing 2 or 3 small spines; lateral face with distinct distal spine. Carpus unarmed.

P 1: 5.2-5.4 × longer than carapace, smooth and sparsely setose, more setose on fingers. Ischium with strong dorsal spine; ventromesially with small blunt subterminal spine not overreaching distal end of ischium, and several low protuberances on proximal half of length. Merus mesially with relatively stout spines roughly in 3 rows (mesial, ventromesial, dorsomesial; dorsal spines smaller), and a few protuberances on proximal ventral surface; length slightly more (1.04-1.15 x) than that of carapace. Carpus 1.4 × length of merus, with several small spines in 2 rows along mesial margin. Palm unarmed, somewhat depressed (height-breadth ratio, 0.8), with lateral and mesial margins subparallel or slightly convex; length 3.0-3.2 × breadth, 1.2 × that of carpus. Fingers relatively stout, moderately gaping, feebly incurved distally, slightly crossing when closed; not spooned along opposable margins; fixed finger inclined somewhat laterally, opposable margin sinuous; movable finger 0.4 × as long as palm, opposable margin with prominent median process (distal margin of process perpendicular to opposable margin) fitting into narrow longitudinal groove on opposite ventromesial face of fixed finger when closed.

P 2-4: Relatively slender, well compressed mesio-laterally, with sparse simple setae, more setose on dactyli. Ischia with 2 short dorsal spines. Meri subequal in length on P 2 and P 3 (female) or very slightly shorter on P 3 than on P 2 (male), shortest on P 4 ( P 4 merus 0.7 × length of P 3 merus); subequally broad on P 2 and P 3, narrower on P 4; dorsal margins unarmed; length-breadth ratio, 3.5-4.0 on P 2, 3.3-3.7 on P 3, 2.5 on P 4; P 2 merus 0.7-0.8 × length of carapace, subequal to length of P 2 propodus; P 3 merus very slightly shorter than P 3 propodus. P 4 merus 0.7 × length of P 4 propodus. Carpi subequal in length on P 2 and P 3 and shorter on P 4; 0.4 × as long as propodus on P 2-4. Propodi subequal in length on P 2 and P 3, shorter on P 4; flexor margin slightly concave in lateral view, with pair of slender terminal spines only. Dactyli subequal in length on P 2-4, slightly less than half as long as propodus; dactylus-carpus length ratio, 1.0 on P 2, 1.1 on P 3, 1.3-1.5 on P 4; flexor margin slightly curving, with 7 or 8 sharp spines loosely arranged, proximally diminishing and nearly perpendicular to margin, ultimate spine slightly more slender than penultimate.

Eggs. Number of eggs carried, 30; size, 1.08 × 1.29 mm - 1.13-1.29 mm.

REMARKS — As mentioned under the remarks of U. clarki n. sp., U. paraplesius resembles U. mesodme n. sp. and U. trispinatus n. sp., sharing the carapace lateral margin having a group of 3 spines on the anterior part remotely separated from another 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. Uroptychus paraplesius is distinguished from U. mesodme by the anterolateral spine of the carapace that is directed anterolaterally instead of straight forward; a pair of epigastric spines are small instead of well-developed with an additional pair of smaller spines between; the eyes are more narrowed distally; the antennal articles 4 and 5 each bear a distinct distomesial spine, instead of being unarmed (although article 5 is distomesially bluntly produced). The relationships between U. paraplesius and U. trispinatus are discussed under the account of the latter species (see below).

The male paratype (poc, 3.2 mm) from the Isle of Pines (MNHN-IU-2013-8574) differs from the other two types (poc, 5.3, 6.0 mm) from the Kai Islands in having the antennal article 5 unarmed and article 4 lacking a small spine at the base of the well-developed distomesial spine, in having the anterolateral spine of the carapace directed straight forward, in having the P 1 ischium and merus longer relative to breadth, and the carpus bearing low eminences along the mesial margin ( Figures 187 View FIGURE 187 , 188 View FIGURE 188 ). These differences appear to be size-related. Discovery of additional material would allow genetic analyses to clarify its systematic status.