Uroptychus tuberculatus, 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 : 535-539

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Uroptychus tuberculatus

n. sp.

Uroptychus tuberculatus n. sp.

Figures 270 View FIGURE 270 , 271 View FIGURE 271

TYPE MATERIAL — Holotype: New Caledonia, Chesterfield Islands . MUSORSTOM 5 Stn DW 355, 19°36’S, 158°43’E, 580 m, 18.X.1986, ♀ 3.5 mm ( MNHN-IU-2014-17005 ) GoogleMaps . Paratypes: Collected with holotype, 2 ♀ 3.6 mm (carapace in 1 ♀ broken) (MNHN-IU-2014-17006) .

ETYMOLOGY„ From the Latin tuberculatus (tuberculate), referring to a tuberculate dorsal surface of the carapace.

DISTRIBUTION„ Chesterfield Islands, in 580 m.

DESCRIPTION„ Small species. Carapace: Broader than long (0.8 × as long as broad); greatest breadth 1.6 × distance between anterolateral spines. Dorsal surface slightly convex from anterior to posterior, with feeble depression between gastric and cardiac regions, and between anterior and posterior branchial regions, sparingly tuberculose; epigastric region with tubercles roughly arranged in transverse row. Lateral margins subparallel; anterolateral spine well-developed, overreaching much smaller lateral orbital spine, followed by row of tubercle-like spines subparalleling another row of small spines above linea anomurica; ridged along posterior third. Rostrum narrow triangular, with interior angle of 22°; length slightly less than half that of remaining carapace, breadth much less than half carapace breadth at posterior carapace margin; dorsal surface deflected ventrally and concave, devoid of tubercles; ventral surface horizontal. Lateral orbital spine slightly anterior to level of anterolateral spine and separated from that spine by its basal breadth. Pterygostomian flap anteriorly angular, produced to well-developed spine; surface with row of spines directly below linea anomurica (spines on anterior half larger than lateral marginal spines of carapace, those in posterior half obsolescent), and scattered obsolescent spines further ventral to this row.

Sternum: Excavated sternum obtusely produced on anterior margin, surface with sharp, elevated ridge in midline. Sternal plastron slightly broader than long, lateral extremities gently divergent posteriorly on sternites 4-7. Sternite 3 moderately depressed; anterior margin strongly concave, bearing deep, broad median notch without flanking spine; anterolaterally sharp angular. Sternite 4 having anterolateral margin relatively short and slightly concave, anteriorly bearing 2 small processes placed side by side; posterolateral margin longer than anterolateral margin. Anterolateral margin of sternite 5 straight divergent posteriorly, slightly rounded on anterior end, about half as long as posterolateral margin of sternite 4.

Abdomen: Smooth and glabrous. Somite 1 dorsally convex from anterior to posterior, without transverse ridge. Somite 2 tergite 2.1-2.3 × broader than long; pleuron posterolaterally blunt, lateral margin feebly concave and weakly divergent posteriorly. Pleuron of somite 3 with blunt lateral end. Telson 0.4 × as long as broad; posterior margin not emarginate, nearly transverse, length 1.3 × that of anterior plate.

Eye: Relatively short, 1.4-1.5 × longer than broad, overreaching midlength of rostrum; mesial and lateral margins convex. Cornea distinctly (in holotype) or somewhat (paratypes) narrower than greatest breadth of remaining eyestalk, length subequal to or slightly less than that of remaining eyestalk.

Antennule and antenna: Ultimate article of antennule 3.4 × longer than high. Antennal peduncle overreaching cornea by full length of article 5, reaching apex of rostrum. Article 2 with small distolateral spine. Antennal scale 2 × broader than article 5, proportionately broad, overreaching midlength of article 5, barely reaching its distal end, with or without small lateral spine. Article 4 distomesially produced to short spine. Article 5 unarmed, 1.5 × longer than article 4; breadth 0.5 × height of antennular ultimate article. Flagellum of 6-7 segments falling short of distal end of P 1 merus.

Mxp: Mxp1 with bases close to each other, slightly separated. Mxp3 barely setose on lateral surface. Coxa with blunt ventrolateral process. Basis with 3 or 4 obsolescent denticles on mesial ridge. Ischium having flexor margin not rounded distally, crista dentata with no distinct denticles. Merus twice as long as ischium, with blunt distolateral spine and 2 similar spines on distal third of flexor margin. Carpus with blunt distolateral spine.

P 1: 6.2 × longer than carapace, relatively slender. Ischium with short blunt dorsal spine, ventromesially with several proximally diminishing spines (distalmost subterminal and well developed) subparalleling another row of 4 or 5 small mesial spines. Merus 1.3-1.4 × longer than carapace, with small mesial and ventral spines, in addition to short, blunt ventral distolateral and distomesial spines; dorsal small spines present or obsolescent. Carpus 1.5 × longer than merus, slightly shorter than palm, mesial margin with obsolescent tubercles or with accompanying row of small spines; dorsal surface sparsely or obsolescently tuberculose. Palm 6 × longer than broad, barely setose; dorsal surface with tubercles near juncture with carpus. Fingers gently incurved distally, crossing when closed, inclined slightly laterally, slightly gaping or not gaping, sparingly with short setae; movable finger one-third length of palm, opposable margin with proximal process fitting to longitudinal groove on opposite ventromesial face of fixed finger when closed.

P 2-4: Relatively broad, compressed mesio-laterally; sparsely setose on meri, carpi and propodi, moderately so on dactyli. Meri successively shorter posteriorly ( P 3 merus 0.9 × length of P 2 merus, P 4 merus 0.8-0.9 × length of P 3 merus), successively slightly broader posteriorly; length-breadth ratio, 3.5-3.6 on P 2, 3.0-3.2 on P 3, 2.3-2.6 on P 4; dorsal margin with a few denticle-like small spines on proximal third; ventromesial margin with 1 or 2 small spines on P 2, ventrolateral margin with small distal spine; P 2 merus 0.8-0.9 × length of carapace, 1.0-1.1 × length of P 2 propodus; P 3 merus 0.8- 0.9 × length of P 3 propodus; P 4 merus 0.7-0.8 × length of P 4 propodus. Carpi subequal, distinctly shorter than dactyli (carpus-dactylus length ratio, 0.7 on P 2, 0.6 on P 3 and P 4); carpus-propodus length ratio, 0.4 on P 2, 0.3 on P 3 and P 4. Propodi subequal on P 3 and P 4, shorter on P 2; flexor margin nearly straight, with pair of terminal spines preceded by 5 (on P 2) or 4 (on P 3 and P 4) spines at most on distal half. Dactyli subequal in length on P 3 and P 4, shorter on P 2, slightly more than half length of propodi (dactylus-propodus length ratio, 0.5-0.6 on P 2, 0.6 on P 3 and P 4), longer than carpi (dactylus-carpus length ratio, 1.4 on P 2, 1.6-1.7 on P 3, 1.7-1.8 on P 4); flexor margin slightly curving, with about 20 spines obscured by setae, ultimate spine slender, penultimate more than 2 × broader than antepenultimate, remaining spines small, shorter than and as broad as ultimate, obliquely directed and very close to one another.

REMARKS„ The spination of the P 2-4 and the shape of sternite 4, especially the posterolateral margin longer than the anterolateral margin, link the species to U. floccus n. sp., U. dualis n. sp. and U. levicrustus Baba, 1988 . However, U. tuberculatus is readily distinguished from U. floccus and U. dualis by the carapace dorsally sparingly tuberculose instead of bearing a row of small epigastric spines, laterally with small instead of strong spines, and by the P 1 merus bearing spines, without a field of three obliquely arranged spines on the proximal mesial surface. Uroptychus levicrustus is different from U. tuberculatus in having the carapace dorsum and the pterygostomian flap both smooth, with at least a well-developed spine on the lateral branchial margin.