Uroptychus angustus,

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

publication ID

http://doi.org/10.5281/zenodo.3760976

DOI

http://doi.org/10.5281/zenodo.3805233

persistent identifier

http://treatment.plazi.org/id/2A1C87B5-FFAE-4D51-FF3D-DADAFB477F25

treatment provided by

Felipe

scientific name

Uroptychus angustus
status

n. sp.

Uroptychus angustus  n. sp.

Figures 12View FIGURE 12, 13View FIGURE 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).GoogleMaps 

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 P 1 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.

P 1: Right P 1 much shorter and narrower than left, probably regenerated. Left P 1 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 P 1). 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 P 1). 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.

P 2-4: Setose like P 1; P 3 and P 4 much shorter on right than on left, presumably regenerated (each article of P 3-4 on right side about 0.8 × that on left side except for propodus). Meri moderately compressed, successively diminishing posteriorly ( P 3 merus 0.9 × length of P 2 merus, P 4 merus 0.8 × length of P 3 merus), equally broad on P 2-4; length-breadth ratio, 5.4 on P 2, 4.6 on P 3, 4.1 on P 4; dorsal margin not crested but rounded, with 5 spines on P 2-4; ventrolateral margin ending in acute spine on P 2-4; ventromesial margin with 3 remotely separated small spines on P 2, unarmed on P 3-4; P 2 merus slightly shorter than carapace, slightly longer than P 2 propodus; P 3 merus 0.9 × length of P 3 propodus; P 4 merus 0.8 × length of P 4 propodus. Carpi successively slightly shorter posteriorly ( P 3 carpus 0.97 length of P 2 carpus, P 4 carpus 0.94 length of P 3 carpus); carpus-propodus length ratio, 0.46 on P 2, 0.48 on P 3, 0.43 on P 4; extensor margin with row of 4 spines paralleling row of 3 spines on lateral surface. Propodi subequal on P 2-3, longer on P 4 (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 P 2, 4 on P 3, 2-4 on P 4. Dactyli well compressed, subequal in length on P 2-4; dactylus-carpus length ratio, 1.1 on P 2, 1.2 on P 3, 1.3 on P 4; dactylus-propodus length ratio, 0.5 on P 2-4; 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 P 2-4 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 P 2-4 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  .