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

Uroptychus eratus n. sp.

Figures 92 , 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 P1 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.

P1: Right P1 missing. Left P1 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.

P2-4: Right P2 and left P3 missing. Right P4 shorter than left P4, especially dactylus much shorter (0.7 x), presumably regenerated. Meri unarmed, sparsely setose, successively shorter posteriorly (P3 merus 0.9 × length of P2 merus; P4 (left) merus 0.9 × length of P3 merus), successively slightly narrower posteriorly; length-breadth ratio, 3.4 on P2, 3.1 on P3, 3.0 on P4; P2 merus three-quarters length of carapace, about as long as P2 propodus; P3 merus 0.8 × length of P3 propodus; P4 merus 0.7 × length of P4 propodus. Carpi successively shorter posteriorly, 0.4 × length of propodus on P2-4. Propodi subequal; flexor margin straight, with pair of terminal spines preceded by 2 movable spines on P2, none on P3 and P4. Dactyli successively longer posteriorly, length half that of propodus on P2-4; dactylus-carpus length ratio, 1.0 on P2, 1.2 on P3 and P4; flexor margin feebly curved, with loosely arranged, subperpendicularly directed (slightly inclined), sharp spines, ultimate somewhat narrower than penultimate on P2, slightly so on P3 and P4, preceded by proximally diminishing spines (8 on left P2, broken on P3, 10 on left P4, 6 on right P4), 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 P2-4 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).

Figures

FIGURE 92 Uroptychus eratus n. sp., holotype, ovigerous female 1.8 mm (MNHN-IU-2013-8515). A, carapace and anterior part of abdomen, proximal part of left P1 included, dorsal. B, same, lateral.C, sternal plastron, with excavated sternum and basal parts of Mxp1. D, telson.E, right antenna, ventral.F, right Mxp3, setae omitted, ventral.G, same, lateral.H, left P1, proximal part,setae omitted, ventral.I, same,proximal part omitted,dorsal. Scale bars:1 mm.

FIGURE 93 Uroptychus eratus n. sp., holotype, ovigerous female 1.8 mm (MNHN-IU-2013-8515). A, left P2,lateral.B, same,distal part, setae omitted, lateral.C, right P3, setae omitted,lateral.D, left P4,setae omitted,lateral. E, same,distal part, setae omitted, lateral.Scale bars: A, C, D, 1 mm; B, E,0.5 mm.