Uroptychus angustus, 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 : 57-61

Uroptychus angustus n. sp.

Figures 12 , 13

TYPE MATERIAL — Holotype: Tonga. BORDAU 2 Stn DW 1602, 20°49’S, 174°57’W, 263-320 m, 15.VI.2000, ov. ♀ 1.9 mm ( MNHN-IU-2014-17284 ).

ETYMOLOGY„ From the Latin angustus (narrow), referring to the ultimate article of antennular peduncle that is as broad as the antennal peduncle, characteristic of the new species. This article is usually much broader than the antennal peduncle in other species.

DISTRIBUTION„ Tonga; 263- 320 m.

DESCRIPTION — Small species. Carapace: slightly broader than long; greatest breadth 1.4 × distance between anterolateral spines. Dorsal surface moderately convex from side to side and anterior to posterior, with weak depression between gastric and cardiac regions, bearing 3 spines in midline (1 on median gastric region, 1 on posterior gastric region, 1 on cardiac region), anteriormost of these flanked by 1 spine on each side; with sparse coarse setae. Lateral margins slightly convex and slightly divergent posteriorly, bearing 6 relatively large spines, first anterolateral, overreaching small lateral orbital spine, remaining spines nearly equidistant on branchial margin, second to fourth somewhat dorsal to level of first, sixth (last) somewhat posterior to midpoint between fifth and posterior end of lateral margin; small tubercle at midlength between first and second spines. Rostrum sharp triangular, with interior angle of 20°, directed slightly dorsally; length slightly more than half that of carapace, breadth half carapace breadth measured at posterior carapace margin; dorsal surface concave, lateral margin with small spine at anterior quarter. Lateral orbital spine about at same level as and close to anterolateral spine. Pterygostomian flap smooth on surface, anteriorly produced to sharp spine.

Sternum: Excavated sternum with sharp ridge in midline of surface, anterior margin triangular, reaching distal end of basal article of Mxp1. Sternal plastron slightly broader than long, lateral extremities gently divergent posteriorly. Sternite 3 moderately depressed, anterior margin moderately concave, with shallow V-shaped median notch, without submedian spines; anterolateral corner angular. Sternite 4 with interrupted transverse ridge bearing coarse setae, anterolateral margin nearly straight, anteriorly ending in strong spine mesially accompanying small tubercle-like spine, length subequal to that of posterolateral margin. Sternite 5 having anterolateral margin strongly convex, shorter than posterolateral margin of sternite 4.

Abdomen: With sparse coarse setae. Somite 1 with transverse ridge. Somite 2 tergite 2.2 × broader than long, with setae transversely arranged on anterior portion; pleural lateral margins concave and strongly divergent posteriorly, posterior end bluntly angular. Pleura of somites 3 and 4 laterally tapering. Telson half as long as broad; posterior plate 1.5 × longer and slightly narrower than anterior plate, posterior margin nearly transverse, not emarginate.

Eye: Slightly overreaching midlength of rostrum, distally narrowed, length 1.9 × breadth; lateral margin slightly convex proximally. Cornea not dilated, half as long as remaining eyestalk.

Antennule and antenna: Ultimate article of antennule 4.0 × longer than high. Antennal peduncle nearly reaching apex of rostrum. Article 2 with small lateral spine. Antennal scale as broad as article 5, slightly falling short of distal end of article 5. Article 4 with strong distomesial spine. Article 5 about twice as long as article 4, with strong, elongate distomesial spine distinctly overreaching rostral tip and another strong ventromesial spine at midlength, breadth slightly more than height of antennular ultimate article. Flagellum consisting of 7 segments, falling short of distal end of P1 merus.

Mxp: Mxp1 with bases broadly separated. Mxp3 basis lacking denticles on mesial ridge. Ischium having flexor margin with rounded distal end mesial to small spine flanked by a few long setae; crista dentata with about 20 very small denticles. Merus 1.7 × longer than ischium, well compressed; mesial face flattish or slightly concave; flexor margin cristiform, angular at distal third, bearing distinct spine and long setae there (absent on right side); with prominent distolateral spine. Carpus also with prominent distolateral spine.

P1: Right P1 much shorter and narrower than left, probably regenerated. Left P1 5.3 × longer than carapace, slender, subcylindrical except for palm and fingers, moderately setose on all articles. Ischium dorsally with sharp strong spine, ventromesially with somewhat smaller subterminal spine proximally followed by 2 much smaller spines (obsolescent on right P1). Merus 1.2 × longer than carapace; 4 rows of spines (2 dorsal, 1 mesial, 1 mesioventral) continued on to carpus. Carpus 1.2 × longer than merus. Palm slightly broadened distally, 4.3 × longer than broad, 1.2 × longer than carpus; mesial margin with 4 spines on proximal two-thirds (unarmed on right P1). Fingers directed somewhat laterally, distally somewhat incurved, crossing when closed; opposable margins sinuous; movable finger one-third length of palm, opposable margin with process of moderate size proximal to midlength, fitting to opposing concave margin of fixed finger when closed.

P2-4: Setose like P1; P3 and P4 much shorter on right than on left, presumably regenerated (each article of P3-4 on right side about 0.8 × that on left side except for propodus). Meri moderately compressed, successively diminishing 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, 5.4 on P2, 4.6 on P3, 4.1 on P4; dorsal margin not crested but rounded, with 5 spines on P2-4; ventrolateral margin ending in acute spine on P2-4; ventromesial margin with 3 remotely separated small spines on P2, unarmed on P3-4; P2 merus slightly shorter than carapace, slightly longer than P2 propodus; P3 merus 0.9 × length of P3 propodus; P4 merus 0.8 × length of P4 propodus. Carpi successively slightly shorter posteriorly (P3 carpus 0.97 length of P2 carpus, P4 carpus 0.94 length of P3 carpus); carpus-propodus length ratio, 0.46 on P2, 0.48 on P3, 0.43 on P4; extensor margin with row of 4 spines paralleling row of 3 spines on lateral surface. Propodi subequal on P2-3, longer on P4 (posteriorly shorter on right side); extensor margin with 2 or 3 spines; flexor margin ending in pair of terminal spines preceded by 4 or 5 relatively broadly separated movable spines on P2, 4 on P3, 2-4 on P4. Dactyli well compressed, subequal in length on P2-4; dactylus-carpus length ratio, 1.1 on P2, 1.2 on P3, 1.3 on P4; dactylus-propodus length ratio, 0.5 on P2-4; flexor margin slightly concave in lateral view, with row of 7-9 loosely arranged, sharp spines diminishing toward base of article, penultimate about twice as broad as antepenultimate as well as ultimate, closer to ultimate than to antepenultimate.

Eggs. Two eggs carried, measuring 0.72 × 0.69 mm.

REMARKS„ Uroptychus angustus keys out in a couplet together with U. tracey Ahyong, Schnabel and Baba, 2015 (see above under the key to species), but they are morphologically largely different. In U. angustus , the carapace dorsal surface bears fewer spines, the antennal article 5 bears a strong distomesial spine instead of being unarmed, and the P2-4 dactyli bear 7-9 loosely arranged instead of 21 closely arranged flexor marginal spines. The spination of the carapace dorsal surface is similar to that of U. setifer n. sp. Their relationships are discussed under the accounts of that species (see below). The spinose carapace and pereopods 1-4, unarmed abdomen, and the long posterolateral margin of sternite 4 link the species to U. anoploetron n. sp., but the carapace in U. angustus has much smaller, fewer spines and the flexor marginal spines of the P2-4 dactyli are loosely arranged, not contiguous to one another as in U. anoploetron .

Uroptychus angustus and U. buantennatus n. sp. (see below) possess the antennal article 5 that is broader than the height of the ultimate article of antennule, an unusual character among the members of the genus. However, this article is as broad as the antennal scale in U. angustus , whereas it is much broader in U. buantennatus .

Figures

FIGURE 12 Uroptychus angustus n. sp., holotype, ovigerous female 1.9 mm (MNHN-IU-2014-17284). A, carapace and anterior abdomen (setae omitted on right half),proximal part ofleft P1 included,dorsal.B, same,lateral.C, sternal plastron,with excavated sternum, basal parts of Mxp1 included.D, telson. E, left antenna,ventral.F, right Mxp3,distal articles omitted,ventral.Scale bars:1 mm.

FIGURE 13 Uroptychus angustus n. sp.,holotype,ovigerous female 1.9 mm (MNHN-IU-2014-17284).A, left P1, proximal part,setae omitted, ventral. B, same, proximal part omitted, dorsal. C, right P2, lateral. D, same, distal part, setae omitted, lateral. E, right P3, setae omitted,lateral.F, right P4, lateral. G, same,distal part, lateral.Scale bars:A,B,C, E,F,1 mm; D,G, 0.5 mm.