Uroptychus pectoralis, 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 : 386-388

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Uroptychus pectoralis

n. sp.

Uroptychus pectoralis n. sp.

Figure 191 View FIGURE 191

TYPE MATERIAL — Holotype: New Caledonia, Chesterfield Islands. MUSORSTOM 5 Stn CC366, 19°45’S, 158°46’E, 650 m, 19.X.1986, with? Chironephthya sp. ( Alcyoniina : Nidaliidae ), ♀ 9.1 mm ( MNHN-IU-2014-16854 ). GoogleMaps

ETYMOLOGY„ From the Latin pectoralis (pertaining to the breast), alluding to the elongate sternal plastron with the anterior margin deeply excavated, a character to separate the species from related species.

DISTRIBUTION„ Chesterfield Islands; 650 m.

DESCRIPTION„ Carapace: As long as broad; greatest breadth 1.6 × distance between anterolateral spines. Dorsal surface glabrous, slightly convex from anterior to posterior, with very shallow depression between gastric and cardiac regions. Lateral margins posteriorly convex; anterolateral spine very small, well separated from, situated distinctly posterior to, and falling short of lateral orbital angle, followed by posteriorly diminishing granules. Rostrum relatively broad triangular, with interior angle of 30°, slightly deflected ventrally; dorsal surface feebly concave; length 0.4 × that of remaining carapace, breadth half carapace breadth at posterior carapace margin. Lateral limit of orbit angular or acuminate, without distinct spine. Pterygostomian flap anteriorly roundish with very tiny spine; surface smooth.

Sternum: Excavated sternum broad triangular and anteriorly blunt, surface with small spine in center. Sternal plastron relatively narrow, about as long as broad; lateral extremities posteriorly divergent. Sternite 3 strongly depressed; anterior margin deeply excavated, representing V-shape, with ill-defined median notch, laterally roundish. Sternite 4 with anterolateral margin long relative to breadth, slightly convex and moderately divergent posteriorly, anteriorly angular, with posteriorly diminishing crenulations; posterolateral margin short, one-third length of anterolateral margin. Sternite 5 with anterolateral margin anteriorly convex, twice as long as posterolateral margin of sternite 4.

Abdomen: Smooth and glabrous. Somite 1 without transverse ridge. Somite 2 tergite 2.3 × broader than long; pleuron with moderately concave, strongly divergent lateral margin, posterolaterally tapering to blunt point. Pleuron of somite 3 with blunt lateral tip. Telson slightly more than half as long as broad; posterior plate twice as long as anterior plate, posterior margin slightly concave.

Eye: Elongate (1.9 × longer than broad), overreaching point two-thirds of rostrum, not reaching apex of rostrum, lateral and mesial margins feebly concave. Cornea slightly dilated, about half as long as remaining eyestalk.

Antennule and antenna: Ultimate article of antennular peduncle 2.3 × longer than high. Antennal peduncle terminating in corneal margin. Article 2 unarmed. Antennal scale 1.7 × broader than article 5, slightly falling short of distal end of article 5. Article 4 unarmed. Article 5 2.5 × longer than article 4, distomesially bearing short blunt spine; breadth less than half height of ultimate antennular peduncle. Flagellum of 21 segments nearly reaching distal end of P 1 merus.

Mxp: Mxp1 with bases close to each other. Mxp3 barely setose laterally. Basis with 1 or 2 denticles on mesial ridge, distal one larger (proximal one missing on right side). Ischium having crista dentata with 22 denticles diminishing toward proximal and distal ends of article, flexor margin distally not rounded. Merus about twice as long as ischium, moderately thick mesio-laterally, unarmed, flexor margin sharply ridged. Carpus unarmed.

P 1: Massive, 4.9 × longer than carapace, unarmed, setose distally, glabrous elsewhere. Ischium dorsally with distal spine of moderate size, ventrally feebly granulose, ventromesially unarmed. Merus with scattered granulate ridges on ventral surface, length slightly more than that of carapace. Carpus moderately depressed on dorsal surface, 1.2 × longer than merus, slightly longer than palm. Palm about 3 × longer than broad, slightly less than twice as long as movable finger. Fingers setose, ending in incurved spine; fixed finger with low eminence at midlength of opposable margin; movable finger with disto-proximally broad proximal process fitting into longitudinal groove on opposite face of fixed finger when closed.

P 2-4: Left P 2, right P 2 and right P 4 detached from body and missing. Remaining legs with scattered long setae. Meri moderately compressed, unarmed; length-breadth ratio, 4.5 on P 3, 4.6 on P 4; P 3 merus very slightly longer than P 3 propodus; P 4 merus 0.9 × as long as and 0.9 × as broad as P 3 merus, 0.9 × as long as P 4 propodus. P 4 carpus 0.9 × length of P 3 carpus; carpus-propodus length ratio, 0.5 on P 3, 0.4 on P 4; carpus-dactylus length ratio, 1.2 on P 3, 1.1 on P 4. Propodi longer on P 4 than on P 3, slightly more than twice as long as dactyli; flexor margin nearly straight, with pair of distal spines slightly distant from juncture with dactylus, preceded by 10 (on P 3) or 8-9 (on P 4) spines along distal threefifths of length. Dactyli much more slender than propodi and strongly curving; flexor margin with 11 or 12 subtriangular spines, ultimate longest, remaining spines somewhat inclined and proximally diminishing; length 0.4 × that of propodi on P 3 and P 4, and 0.8 × that of carpi on P 3, 0.9 × on P 4.

REMARKS — Uroptychus pectoralis resembles U. gordonae Tirmizi, 1964 from the Maldives, U. laperousazi Ahyong & Poore, 2004 and U. latus Ahyong & Poore, 2004 , both from southern Australia, sharing the carapace with the small anterolateral spine only, the P 2-4 dactyli with proximally diminishing triangular spines and sternite 3 without submedian spines. The new species is distinguished from these three species by the following differences: the carapace is as long as instead of much broader than long, as also is the sternal plastron; sternite 3 is more deeply excavated on the anterior margin; the anterolateral spine of the carapace is distinctly posterior rather than directly lateral to the lateral orbital spine. The type material of U. gordonae (male holotype and 1 female paratype, BMNH 1966.2.3.17-18) examined on loan shows that the flexor margins of the P 2-4 propodi each bear 2 or 3 single spines proximal to the distal pair (8-10 spines in U. pectoralis ); also, the flexor marginal spines of the dactyli are less numerous (6-8 versus 11 or 12).