Uroptychus seductus, 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 : 458-462

Uroptychus seductus n. sp.

Figures 229 , 230

TYPE MATERIAL — Holotype: Indonesia, Tanimbar Islands. KARUBAR Stn CP82, 9°32’S, 131°02’E, 219- 215 m, with Thouarella sp. ( Calcaxonia , Primnoidae ), 4.XI.1991, ov. ♀ 2.8 mm ( MNHN-IU-2014-16942 ) . Paratypes: Collected with holotype, 4 ov. ♀ 2.3-2.8 mm (MNHN-IU-2014-16943) .

ETYMOLOGY„ From the Latin seductus (remote, apart), referring to the flexor marginal spines of P2-4 dactyli, which are remote from one another, a character to separate the species from U. annae n. sp.

DISTRIBUTION„ Tanimbar Islands ( Indonesia); 215- 219 m.

SIZE„ Ovigerous females, 2.3-2.8 mm; no males were collected.

DESCRIPTION„ Small species. Carapace: 1.1 × broader than long (0.9 × as long as broad); greatest breadth 1.7 × distance between anterolateral spines. Dorsal surface smooth, with scattered short setae on surface, slightly convex from anterior to posterior, without depression. Lateral margins slightly convexly divergent posteriorly, with 7 spines, 3 on hepatic margin and 4 on branchial margin: first anterolateral, strong, overreaching lateral orbital spine; second and third small and ventral to level of remainder; fourth to seventh equidistant, fourth and fifth as large as or somewhat smaller than first; sixth small; seventh small, obsolete or absent, situated at midlength of posterior branchial margin. Rostrum narrow triangular, with interior angle of 20-30°; dorsal surface deeply concave; ventral surface straight horizontal; lateral margin straight or somewhat concave, with subapical spine (absent in holotype); length 0.4-0.5 × that of remaining carapace, breadth less than half carapace breadth at posterior carapace margin. Lateral orbital spine much smaller than, directly mesial and close to anterolateral spine. Pterygostomian flap anteriorly angular, produced to sharp spine; surface with a few to several small spines, one of these consistent directly below linea anomurica (below third or between third and fourth of lateral marginal spines of carapace).

Sternum: Excavated sternum having anterior margin convex, surface with longitudinal ridge in midline. Sternal plastron 0.8-0.9 × as long as broad; lateral extremities slightly divergent posteriorly. Sternite 3 shallowly depressed, anterior margin shallowly excavated, with 2 small submedian spines separated by small notch, laterally angular or with 2 small spines place side by side. Sternite 4 about as broad as sternite 5; anterolateral margin nearly straight and smooth, anteriorly bearing a few small spines, length twice that of posterolateral margin. Sternite 5 about as long as sternite 4, anterolateral margin 1.3 × longer than posterolateral margin of sternite 4.

Abdomen: Tergites smooth and sparsely setose. Somite 1 smooth, not transversely ridged. Somite 2 tergite 2.0-2.4 × broader than long, pleuron posterolaterally blunt, lateral margin feebly concave, weakly divergent posteriorly. Pleuron of somite 3 with rounded lateral margin. Telson 0.3-0.4 × as long as broad, posterior plate slightly shorter than anterior plate, broadly concave on posterior margin.

Eye: 2 × longer than broad, somewhat narrowed distally, overreaching midlength of, not reaching apex of rostrum. Cornea less than half as long as remaining eyestalk.

Antennule and antenna: Ultimate article of antennular peduncle 2.6-2.9 × longer than high. Antennal peduncle terminating in distal margin of cornea. Article 2 with strong lateral spine. Antennal scale 1.4 × broader than article 5, overreaching antennal peduncle by full length of article 5. Distal 2 articles each with strong distomesial spine; article 5 1.1- 1.2 × longer than article 4, breadth 0.7-0.8 × height of ultimate article of antennule. Flagellum consisting of 6-8 segments, falling far short of distal end of P1 merus.

Mxp: Mxp1 with bases broadly separated. Mxp3 with sparse long setae on lateral face. Basis without denticles on mesial ridge. Ischium with small spine and long setae lateral to rounded distal end of flexor margin; crista dentata with about 20 distally and proximally diminishing denticles. Merus 1.5 × longer than ischium, strongly compressed mesiolaterally, flexor margin sharply ridged, bearing 2 small close spines on angularly produced portion at distal third. Strong distolateral spine on merus and carpus.

P1: Slender, 4.5-4.8 × length of carapace, with distally softened long setae. Ischium with 2 dorsal spines, distal one strong, proximal one small, ventrally with well-developed subterminal spine on mesial margin. Merus 1.1-1.2 × longer than carapace, with 2 distoventral (1 large mesial, 1 lateral), 1 distodorsal (mesial), 3 proximomesial, and 1 or 2 small or obsolescent ventral spines. Carpus ventrally with distomesial and distolateral spine, length 1.1-1.2 × that of merus. Palm 3.1-3.3 × longer than broad, 1.1-1.2 × longer than carpus. Fingers distally incurved, crossing when closed; movable finger about half as long as palm, opposable margin with low median process fitting to groove proximal to low median eminence on opposable margin of fixed finger.

P2-4: Relatively short and broad, somewhat compressed mesio-laterally, setose like P1. Meri subequal in length on P2 and P3, shortest on P4 (P4 merus 0.8 × length of P3 merus), subequally broad on P2-4; length-breadth ratio, 3.5 on P2, 3.2-3.4 on P3, 2.7-2.9 on P4; dorsal margins with 2-5 eminences supporting setae, proximal 2 or 3 of these replaced by very small spines usually on P2, occasionally on P3; ventromesial margin with 1 or 2 very small spines each accompanying long setae on P2 only, distal one terminal, proximal one near proximal end of article; ventrolateral margin distally ending in spine; P2 merus 0.8 × length of carapace, 1.1-1.2 × length of P2 propodus; P3 merus subequal to length of P3 propodus; P4 merus 0.8 × length of P4 propodus. Carpi subequal, shorter than dactyli (carpus-dactylus length ratio, 0.8 on P2 and P3, 0.7 on P4), slightly less than half length (0.47-0.48 on P2, 0.41-0.44 on P3 and P4) of propodi. Propodi subequal on P3 and 4, slightly shorter on P2; flexor margin slightly convex, ending in pair of spines preceded by 6-7 slender spines on P2, 5 or 6 spines on P3 and P4. Dactyli 0.6 × length of propodi on P2-4, longer than carpi (dactylus-carpus length ratio, 1.2 on P2, 1.3 on P3, 1.4 on P4), markedly narrowed distally; flexor margin slightly curving, with 6-8 spines loosely arranged (penultimate, antepenultimate and distal quarter spines spaced by twice their basal breadth), ultimate slender, penultimate to distal quarter equally strong and somewhat inclined, remaining spines short, slender and more obliquely directed.

Eggs. Number of eggs carried, 6-8; size, 1.70 mm × 1.90 mm.

REMARKS„ The species strongly resembles U. oxymerus Ahyong & Baba, 2004 from northwestern Australia, U. tridentatus ( Henderson, 1885) as redefined in this paper (see below), and U. annae n. sp. in the spination of the carapace lateral margin, in having a small spine lateral to the distal end of flexor margin of Mxp3 ischium, and in having the antennal articles 4 and 5 each bearing a strong distomesial spine. Uroptychus seductus is readily distinguished from these congeners by the P2-4 dactyli that are more strongly tapering, with more widely spaced flexor marginal spines.

The P2 and P3 propodi each bear a row of flexor marginal spines along the entire length, in addition to the distal pair, in U. seductus and U. tridentatus (P4 is unknown in U. tridentatus ) whereas only a few spines proximal to the distal pair in U. annae and U. oxymerus . Uroptychus seductus differs from U. tridentatus , in addition to the difference in the spination of P2-3 dactyli (see above), in having the antennal scale overreaching the antennal peduncle by the full length of article 5 instead of reaching at most the second segment of flagellum.

The new species is also close to U. vicinus n. sp. in the spination of the carapace and P2-4, and the shapes of the antenna and sternum. Their relationships are discussed under the remarks of that species (see below).

Figures

FIGURE 229 Uroptychus seductus n. sp., A-G, holotype, ovigerous female 2.8 mm (MNHN-IU-2014-16942); H, I, paratype, ovigerous female 2.8 mm (MNHN-IU-2014-16943).A,carapace and anterior part of abdomen,dorsal.B, same,abdomen and setae omitted,lateral. C, anterior part of sternal plastron, with excavated sternum and basal parts of Mxp1. D, telson. E, left antenna, ventral.F, right Mxp3, ventral.G, same,merus and carpus,lateral.H, carapace,dorsal.I, carapace,showing arrangement of spines along lateral margin and on pterygostomian flap, lateral. Scale bars: 1 mm.

FIGURE 230 Uroptychus seductus n. sp., holotype, ovigerous female 2.8 mm (MNHN-IU-2014-16942). A, right P1, dorsal. B, same, proximal part, setae omitted, ventral.C, left P2,lateral.D, left P3,setae omitted,lateral. E, left P4,setae omitted, lateral. Scale bars: 1 mm.