Uroptychus eratus, 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 : 207-210

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Uroptychus eratus

n. sp.

Uroptychus eratus n. sp.

Figures 92 View FIGURE 92 , 93 View FIGURE 93

TYPE MATERIAL — Holotype: Philippines. MUSORSTOM 1 Stn CP 03, 14°01’N, 120°15’E, 183-185 m, 19.III.1976, ov.

♀ 1.8 mm ( MNHN-IU-2013-8515 ).


ETYMOLOGY„ Front the Greek eratos (lovely), alluding to the small lovely species.

DISTRIBUTION„ Off southeastern Luzon, Philippines; 183- 185 m.

DESCRIPTION„ Small species. Carapace: Broader than long (length 0.75 × breadth); greatest breadth 1.9 × distance between anterolateral spines. Dorsal surface smooth, somewhat convex from anterior to posterior, smoothly continued on to rostrum. Lateral margins smoothly divergent posteriorly, convex on posterior fourth; anterolateral spine of moderate size (missing on left side, presumably broken), overreaching much smaller lateral orbital spine. Rostrum sharp triangular, with interior angle of 32°; length 0.4 × that postorbital carapace length, breadth less than half carapace breadth measured at posterior carapace margin; dorsal surface slightly concave; ventral surface horizontal. Lateral orbital spine small, situated directly mesial to but separated from anterolateral spine by basal breadth of latter spine. Pterygostomian flap anteriorly angular, ending in small spine, surface smooth.

Sternum: Excavated sternum with convex anterior margin, surface with ridge in midline. Sternal plastron 1.2 × broader than long, lateral extremities successively broader posteriorly. Sternite 3 shallowly depressed, anterior margin gently concave without median notch and submedian spines. Sternite 4 with anterolateral margin slightly convex, anteriorly produced to small spine; posterolateral margin short, one-third length of anterolateral margin. Anterolateral margin of sternite 5 strongly convex, 1.7 × longer than posterolateral margin of sternite 4.

Abdomen: Tergites smooth and glabrous. Somite 1 somewhat convex from anterior to posterior, without transverse ridge. Somite 2 tergite 1.9 × broader than long; pleural lateral margins weakly concave and moderately divergent posteriorly, with rounded posterolateral terminus. Pleuron of sternite 3 with blunt lateral end. Telson 0.3 × as long as broad; posterior plate feebly concave; length 0.6 × that of anterior plate.

Eye: 1.5 × longer than broad, distally narrowed, slightly falling short of apex of rostrum. Cornea not dilated, length one-third that of remaining eyestalk.

Antennule and antenna: Ultimate article of antennular peduncle 1.9 × longer than high. Antennal peduncle reaching distal margin of cornea. Article 2 with well-developed distolateral spine. Antennal scale slightly broader than article 5, terminating in distal end of article 5, slightly overreaching eye. No spine on articles 4-5; article 5 1.3 × length of article 4, breadth 0.6 × height of antennular ultimate article. Flagellum consisting of 6 segments, slightly overreaching P 1 merus.

Mxp: Mxp1 with bases broadly separated. Mxp3 basis with a few obsolescent denticles on mesial ridge. Ischium with very small numerous denticles on crista dentata; flexor margin not rounded distally. Merus 2.1 × longer than ischium, flexor margin not cristate but somewhat roundly ridged with 2 close tiny spines distal to point two-thirds of length; distolateral spine small but distinct. Carpus with small distolateral spine and eminence at proximal part of extensor margin.

P 1: Right P 1 missing. Left P 1 with sparse short setae, length 3.4 × that of carapace. Ischium with short, subtriangular dorsal spine, ventromesially bearing a few obsolescent denticles on proximal half, subterminal spine absent. Merus threequarters length of carapace; distoventral (mesial and lateral) spines distinct, and a few scattered small spines on ventral surface. Carpus 1.1 × longer than merus; ventrally bearing obsolescent distomesial and distolateral spines, unarmed elsewhere. Palm relatively high dorsoventrally, 2.3 × longer than broad, 1.6 × longer than carpus. Fingers broad relative to length, depressed, distally incurved, crossing when closed, and curving ventrally; movable finger half as long as palm, opposable margin with bluntly subtriangular (in dorsal view) process proximal to midlength; opposing margin of fixed finger sinuous.

P 2-4: Right P 2 and left P 3 missing. Right P 4 shorter than left P 4, especially dactylus much shorter (0.7 x), presumably regenerated. Meri unarmed, sparsely setose, successively shorter posteriorly ( P 3 merus 0.9 × length of P 2 merus; P 4 (left) merus 0.9 × length of P 3 merus), successively slightly narrower posteriorly; length-breadth ratio, 3.4 on P 2, 3.1 on P 3, 3.0 on P 4; P 2 merus three-quarters length of carapace, about as long as P 2 propodus; P 3 merus 0.8 × length of P 3 propodus; P 4 merus 0.7 × length of P 4 propodus. Carpi successively shorter posteriorly, 0.4 × length of propodus on P 2-4. Propodi subequal; flexor margin straight, with pair of terminal spines preceded by 2 movable spines on P 2, none on P 3 and P 4. Dactyli successively longer posteriorly, length half that of propodus on P 2-4; dactylus-carpus length ratio, 1.0 on P 2, 1.2 on P 3 and P 4; flexor margin feebly curved, with loosely arranged, subperpendicularly directed (slightly inclined), sharp spines, ultimate somewhat narrower than penultimate on P 2, slightly so on P 3 and P 4, preceded by proximally diminishing spines (8 on left P 2, broken on P 3, 10 on left P 4, 6 on right P 4), penultimate spine largest.

Eggs. Two eggs carried; size, 0.84 × 0.94 mm - 0.90 × 0.96 mm.

REMARKS — The carapace that is distinctly broader than long and posteriorly broadened, with well-developed anterolateral spines links the species to U. patulus Ahyong & Poore, 2004 from southeastern Australia. However, U. eratus is clearly different from that species in having: the sternite 3 anterior margin gently instead of strongly excavated; the eyes reaching nearly the apex of the rostrum instead of terminating in the midlength; the antennal article 2 bearing a distolateral spine instead of being unarmed; and the P 2-4 dactyli much shorter, at least half as long as the propodi instead of much more than so, with the flexor margin slightly curving instead of strongly so, and more noticeably bearing 9-11 instead of 20 closely arranged spines. In addition, U. patulus is a medium-sized species, the largest ovigerous female recorded being 12.6 mm (postorbital carapace length, 8.3 mm).