Uroptychus volsmar, 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 : 554-558

Uroptychus volsmar n. sp.

Figures 280 , 281

TYPE MATERIAL — Holotype: New Caledonia, Hunter and Matthew Islands . VOLSMAR Stn DW 16, 22°25’S, 171°41’E, 420-500 m, 03.VI.1989, ♂ 3.0 mm ( MNHN-IU-2011-5968 ) . Paratypes: New Caledonia, Hunter and Matthew Islands. VOLSMAR, collected with holotype, 1 ♂ 2.7 mm (MNHN-IU-2011-5969) . – Stn DW 07, 22°26’S, 171°44’E, 325-400 m, 01.VI.1989, 1 ov. ♀ 2.5 mm (MNHN-IU-2011-5964). New Caledonia, Loyalty Ridge. MUSORSTOM 6 Stn DW 406, 20°40.65’S, 167°06.80’E, 373 m, 15.II.1989, 1 ov. ♀ 2.5 mm (MNHN-IU-2014-17024) .

ETYMOLOGY„ Named for the cruise VOLSMAR, by which the holotype was collected; used as a noun in apposition.

DISTRIBUTION„ Loyalty Islands and Hunter and Matthew Islands; 373- 500 m.

SIZE„ Males, 2.7, 3.0 mm; ovigerous females, 2.5 mm.

DESCRIPTION„ Small species. Carapace: Slightly broader than long (0.9 × as long as broad); greatest breadth 1.5 × distance between anterolateral spines. Dorsal surface smooth, sparsely with soft setae, with distinct depression between gastric and cardiac regions; gastric region somewhat convex, cardiac region well convex, indistinctly separated from branchial region. Lateral margins slightly convexly divergent posteriorly; anterolateral spine short and basally stout, somewhat dorsal in position, very close to but distinctly posterior to level of lateral orbital spine; small spines along branchial margin. Rostrum broad triangular, with interior angle of 30-35°, nearly straight, directed slightly dorsally; dorsal surface concave; length slightly less than half that of remaining carapace, breadth half carapace breadth at posterior carapace margin. Lateral orbital spine relatively large, subequal to anterolateral spine. Pterygostomian flap with scattered denticles or small spines on surface, anterior margin somewhat angular, produced to small spine.

Sternum: Excavated sternum with moderately or strongly convex anterior margin, bearing ridge in midline on surface. Sternal plastron about as long as broad, lateral extremities subparallel between sternites 4 and 7. Sternite 3 shallowly depressed; anterior margin gently concave with semioval median sinus flanked by very small or obsolescent spine. Sternite 4 having anterolateral margin as long as posterolateral margin, convex with bluntly angular anterior end. Anterolateral margins of sternite 5 subparallel but anteriorly convex, length 0.6-0.7 × that of posterolateral margin of sternite 4.

Abdomen: Smooth, with sparse long setae. Somite 2 tergite 2.8 × broader than long; pleuron posterolaterally blunt, lateral margin somewhat concave, moderately divergent posteriorly. Pleuron of somite 3 with blunt lateral terminus. Telson about half as long as broad; posterior plate semicircular and feebly emarginate on posterior margin, length 1.3 × that of anterior plate.

Eye: Elongate (2 × longer than broad), slightly falling short of rostral tip; distally narrowed, lateral margin strongly convex. Cornea not dilated, length about half or slightly less than half that of remaining eyestalk.

Antennule and antenna: Antennular ultimate article 3.2-3.4 × longer than high. Antennal peduncle overreaching rostrum. Article 2 with distolateral spine. Antennal scale 1.3 × broader than article 5, terminating in or slightly overreaching distal end of article 4. Article 4 with small distomesial spine. Article 5 unarmed, length 1.7-1.8 × that of article 4. Flagellum consisting of 12-14 segments, not reaching distal end of P1 merus.

Mxp: Mxp1 with bases distinctly separated from each other. Mxp3 basis lacking denticles on proximally lobe-like mesial ridge. Ischium with tuft of long setae lateral to rounded distal end of flexor margin; crista dentata with very small obsolescent denticles. Merus 2.3 × longer than ischium, distolateral spine short or obsolescent; flexor margin moderately ridged without spine. Carpus also spineless.

P1: 6.7-7.0 × longer than carapace, sparingly with long, soft, plumose setae. Ischium with short distodorsal spine, ventromesially unarmed. Merus unarmed, 1.5-1.7 × longer than carapace. Carpus 1.4 × longer than merus, unarmed. Palm 3.7-5.0 × longer than broad, about as long as palm. Fingers relatively narrow and slightly incurved distally, feebly crossing when closed, curving slightly ventrally, somewhat or greatly gaping; when strongly gaping, opposable margins touching each other at distal portion, crossing at tip when closed; movable finger 0.4 × length of palm, opposable margin with obtuse proximal process or with additional lower prominence distal to it, irrespective of sex; opposable margin of fixed finger with or without prominence distal to midlength.

P2-4: Sparingly with long, distally soft setae, moderately compressed mesio-laterally. Meri unarmed, successively shorter posteriorly (P3 merus 0.9 × length of P2, P4 merus 0.9 × length of P3 merus), equally broad on P2-4; length-breadth ratio, 4.0-4.4 on P2, 3.7-3.9 on P3, 3.5-3.8 on P4; P2 slightly shorter than carapace, slightly longer than P2 propodus; P3 merus 0.9 × length of P3 propodus; P4 merus 0.8-0.9 × length of P4 propodus. Carpi subequal; slightly less than one-third as long as propodus. Propodi subequal on P2-4, shorter on P2 than on P3 and P4 and subequal on P3 and P4 or longer on P3 than on P4; flexor margin nearly straight, with pair of terminal spines only. Dactyli subequal, 1.2 × longer than carpi and 0.3-0.4 × as long as propodi on P2-4; flexor margin straight, with 7 spines: ultimate slender; penultimate prominent, twice as broad as and very close to ultimate, remaining proximal spines loosely arranged, diminishing toward base of article, nearly perpendicular to margin (proximal 2 somewhat inclined), antepenultimate half as broad as penultimate, proximal-most very small and often obsolete.

Eggs. Number of eggs carried, 2-12; size, 0.88 mm × 0.92 mm - 1.10 mm × 1.20 mm.

REMARKS„ The new species resembles U. laurentae n. sp., U. paenultimus Baba, 2005 , and U. toka Schnabel, 2009 in having the anterolateral spine of the carapace close to the lateral orbital spine, the sternites 4-7 with subparallel lateral extremities, the antennal scale being short, ending at most in the midlength of antennal article 5, and the P2-4 dactyli bearing the penultimate flexor marginal spine fully twice as broad as the antepenultimate. Uroptychus volsmar is differentiated from U. laurentae and U. paenultimus by the P2-4 dactyli that bear flexor marginal spines directed perpendicularly instead of obliquely. In addition, the distal two of these spines are different in size: the penultimate spine is twice as broad as the ultimate spine in U. volsmar , 9 times broader in U. laurentae , 5 times broader in U. paenultimus . Uroptychus volsmar differs from U. toka in having the eyes distally narrowed rather than nearly uniformly

broad from proximal to distal; the carapace dorsal surface is smooth instead of bearing denticle-like small spines on the gastric and epigastric regions; and the lateral orbital spine is subequal to instead of distinctly larger than the anterolateral spine of the carapace.

The shape of the sternal plastron, the spination of the P2-4 propodi and dactyli link this new species to U. turgidus n. sp. However, U. volsmar is readily distinguished from that species by the lateral orbital spine that is subequal to instead of much stronger than the anterolateral spine of the carapace, and by the P2-4 dactyli that are slightly (1.2 ×) instead of much (1.6 ×) longer than the carpi. In addition, the distinct lateral spines and pronounced inflation on the posterior branchial margin as displayed by U. turgidus are missing in U. volsmar .

Figures

FIGURE 280 Uroptychus volsmar n. sp., holotype, male 3.0 mm (MNHN-IU-2011-5968). A, carapace and anterior part of abdomen, proximal articles of right P1 included,dorsal.B, same,lateral.C, lateral margin of carapace,right,setae omitted,dorsal.D,sternal plastron,with excavated sternum and basal parts of Mxp1.E, telson.F, left antenna,ventral.G, left Mxp3,ventral.H, same,lateral.Scale bars:1 mm.

FIGURE 281 Uroptychus volsmar n. sp.,holotype, male 3.0 mm (MNHN-IU-2011-5968). A, right P1, proximal part, setae omitted, ventral. B, same, dorsal. C, right P2, lateral. D, same, distal part, setae omitted, lateral. E, right P3, setae omitted, lateral.F, right P4, setae omitted, lateral. Scale bars: 1 mm.