Uroptychus modicus, 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 : 322-326

Uroptychus modicus n. sp.

Figures 154 , 155

TYPE MATERIAL — Holotype: New Caledonia, Isle of Pines. SMIB 8 DW198, 22°51.6’S, 167°12.4’E, 414-430 m, 1.II.1993, ♀ 6.8 mm ( MNHN-IU-2014-16740 ) . Paratypes: New Caledonia, Isle of Pines. SMIB 2 Stn DW05, 22°56’S, 167°15’E, 398-410 m, 17.IX.1986, 1 ov. ♀ 6.0 mm, 1 ♀ 5.8 mm (MNHN-IU-2014-16741) . New Caledonia, Norfolk Ridge. BA- THUS 3 Stn CP833, 23°03’S, 166°58’E, 441-444 m, 30.XI.1993, 1 ov. ♀ 6.6 mm (MNHN-IU-2014-16742).

ETYMOLOGY„ From the Latin modicus (medium, moderate), alluding to the moderate size of the species.

DISTRIBUTION„ Isle of Pines and Norfolk Ridge; 398- 444 m.

SIZE„ Females, 5.8-6.8 mm; ovigerous females from 6.0 mm; males have not been collected. DESCRIPTION„ Medium-sized species. Carapace: 1.1 × broader than long (0.9 × as long as broad); greatest breadth 1.7 × distance between anterolateral spines. Dorsal surface weakly convex from anterior to posterior, with shallow depression between indistinct gastric and cardiac regions, covered with short fine setae; epigastric region with transverse row of 7 or 9 small spines (1 spine in midline flanked by 3 or 4 spines) preceded by depressed rostrum. Lateral margins convexly divergent posteriorly; anterolateral spine well developed, overreaching lateral orbital spine, followed by 2 small hepatic marginal spines in line with anterolateral spine and distinctly ventral to following lateral spines; branchial margin with 4 spines, anterior 3 strong and subequal, last smaller or tiny, followed by ridge leading to posterior end of margin; first spine on branchial margin with accompanying small, often obsolete spine mesial to it. Rostrum broad triangular, with interior angle of about 30°; dorsal surface concave, strongly depressed from level of gastric region; lateral margin with a few obsolescent spinules distally; length 0.5-0.6 × that of remaining carapace, breadth less than carapace breadth at posterior carapace margin. Lateral orbital spine small, slightly anterior to level of anterolateral spine. Pterygostomian flap anteriorly angular, produced to small spine; surface with short soft setae.

Sternum: Excavated sternum with strongly convex anterior margin, surface bearing low, relatively broad ridge in midline. Sternal plastron as long as broad, lateral extremities between sternites 4 and 7 gently divergent posteriorly. Sternite 3 strongly depressed, anterior margin in broad V-shape bearing small or obsolescent median notch without submedian spines; anterolateral angle well produced. Sternite 4 having anterolateral margin nearly straight or slightly concave, anteriorly roundish with a few tubercles or denticles; posterolateral margin relatively short, slightly more than half length of anterolateral margin. Anterolateral margin of sternite 5 anteriorly rounded, about as long as posterolateral margin of sternite 4.

Abdomen: Smooth, sparingly with short, soft setae. Somite 1 without transverse ridge. Somite 2 tergite 2.6-2.8 × broader than long; pleuron anterolaterally bluntly rectangular, posterolaterally blunt angular; lateral margin concavely divergent posteriorly. Pleuron of somite 3 laterally tapering. Telson half as long as broad; posterior plate somewhat concave on posterior margin, length 1.5-1.6 × that of anterior plate.

Eye: Relatively small, elongate (1.9-2.1 × longer than broad), slightly narrowed distally, and reaching midlength of rostrum. Cornea more than half as long as remaining eyestalk.

Antennule and antenna: Ultimate article of antennular peduncle 3.3-3.8 × longer than high. Antennal peduncle extending far beyond cornea. Article 2 with short, distinct distolateral spine. Antennal scale slightly falling short of to slightly overreaching distal end of article 5, breadth 1.5-1.6 × that of article 5. Distal 2 articles each armed with strong distomesial spine; article 5 1.7-1.9 × longer than article 4, breadth 0.6-0.7 × height of ultimate article of antennule. Flagellum consisting of 10-13 segments, reaching distal end of P1 merus.

Mxp: Mxp1 with bases broadly separated. Mxp3 basis without denticles on mesial ridge. Ischium with obsolescent denticles on crista dentata; flexor margin distally not rounded. Blunt distolateral spines on each of merus and carpus. Merus 2 × longer than ischium, flexor margin roundly ridged, bearing 2 small spines distal to point two-thirds of length.

P1: Moderately massive, 4.6 × longer than carapace, covered with soft, fine setae. Ischium dorsally with basally broad, short spine, ventromesially with tubercle-like spines. Granulose short ridges supporting setae on merus and carpus. Merus as long as carapace, with 2 stout mesial, 2 distodorsal, and 2 distoventral spines. Carpus 1.2 × length of merus, with 3 terminal spines: dorsal, ventromesial, ventrolateral. Palm 2.8 × longer than broad, 1.2 × longer than carpus, unarmed. Fingers short relative to breadth, curving ventrally, distally crossing when closed; opposable margins not gaping, that of movable finger with low or moderate-sized proximal process proximal to position of low eminence on opposite margin of fixed finger; movable finger half as long as palm.

P2-4: Setose like P1. Meri mesio-laterally compressed, successively shorter posteriorly (P3 merus 0.9 × length of P2 merus, P4 merus 0.9 × length of P3 merus), breadths subequal on P2-4; dorsal and ventrolateral margins smooth, bearing terminal spine only, but ventrolateral terminal spine obsolete on P4; length-breadth ratio, 3.5-3.6 on P2, 3.0-3.4 on P3, 3.1-3.9 on P4; P2 merus 0.7 × length of carapace, 1.0 × length of P2 propodus; P3 merus 0.9 × length of P3 propodus; P4 merus 0.7-0.8 × length of P4 propodus. Carpi subequal, unarmed, slightly shorter than dactyli (carpus-dactylus length ratio, 0.9 on P2, 0.8 on P3 and P4); carpus-propodus length ratio, 0.46-0.49 on P2, 0.42-0.46 on P3, 0.41-0.42 on P4; slightly shorter than

dactyli, unarmed. Propodi subequal in length on P2-4; flexor margin feebly curving, ending in pair of spines preceded by 3 or 4 single movable spines on distal third on P2, 2 or 3 spines on P3, 1 or 2 spines on P4, distalmost of these single spines much more distant from distal pair than from distal second. Dactyli relatively stout; dactylus-propodus length ratio, 0.5-0.6 on P2-4; dactylus-carpus length ratio, 1.1 on P2, 1.2 on P3, 1.3 on P4; flexor margin gently curving, with 18-21 acute spines subperpendicular to margin on distal portion, somewhat inclined on proximal portion, ultimate spine more slender than penultimate, remaining spines relatively close to one another but not contiguous, diminishing toward proximal end of article.

Eggs. Number of eggs carried, 19-30; size, 1.42 mm × 1.58 mm - 1.42 mm × 1.83 mm.

REMARKS — The spination of the carapace lateral margin and the shape of the rostrum and eyes displayed by U. modicus n.s p. are very similar to those of U. baeomma n. sp. (see above). Uroptychus modicus is distinguished from that species by the following: the transverse row of epigastric spines is distinct in U. modicus , absent in U. baeomma ; the flexor spines of the P2-4 dactyli are more numerous on U. modicus (18-21 versus 8-10); sternite 3 has the anterior margin deeply excavated in V-shape with a small or obsolescent median notch in U. modicus , whereas it is shallowly excavated, with a deep median notch in U. baeomma ; and the antennal articles 4 and 5 each bear a strong instead of tiny or obsolescent distomesial spine.

The spination of P2-4, especially the dactyli ending in a small ultimate spine proximally preceded by triangular spines, and sternite 3 having a V-shaped anterior margin without submedian spines suggest that U. modicus resembles U. posticus n. sp. Characters distinguishing these species are outlined under U. posticus (see below).

Figures

FIGURE 154 Uroptychus modicus n. sp.,holotype,female 6.8 mm (MNHN-IU-2014-16740). A, carapace and anterior part of abdomen,proximal part of left P1 included,dorsal. B, same, abdomen denuded, lateral.C, sternal plastron,with excavated sternum and basal parts of Mxp1. D, telson.E, left antenna,ventral.F, left Mxp3,setae omitted,ventral.G, same, lateral.H, left P1, proximal part omitted,dorsal. Scale bars: A,B,G, 5 mm; C-F,1 mm.

FIGURE 155 Uroptychus modicus n.sp.,holotype,female 6.8 mm (MNHN-IU-2014-16740).A, left P2,lateral.B, same,setae omitted,lateral.C, same,distal part, setae omitted, lateral. D, left P3, setae omitted, lateral. E, same, distal part, setae omitted, lateral. F, left P4, lateral.G, same, distal part, lateral. Scale bars: 1 mm.