Uroptychus vicinus, 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 : 550-554

Uroptychus vicinus n. sp.

Figures 278 , 279

TYPE MATERIAL — Holotype: New Caledonia, Norfolk Ridge. BATHUS 3 Stn CP833, 23°03’S, 166°58’E, 441-444 m, 30.XI.1993, ♂ 3.3 mm ( MNHN-IU-2014-17019 ) . Paratypes: Vanuatu. MUSORSTOM 8 Stn CP1026, 17°50.35’S, 168°39.33’E, 437-504 m, 28.IX.1994, 1 ov. ♀ 3.3 mm (MNHN-IU-2014-17020) . New Caledonia. MUSORSTOM 4 Stn CP180, 18°57’S, 163°18’E, 450 m, 18.IX.1985, 1 ♂ 3.1 mm, 1 ov. ♀ 2.9 mm (MNHN-IU-2014-17021) . New Caledonia, Loyalty Ridge. MUSORSTOM 6 Stn DW428, 20°23.54’S, 166°12.57’E, 420 m, on Thouarella sp. ( Alcyonacea : Primnoidae ), 17.II.1989, 1 ov. ♀ 3.2 mm (MNHN-IU-2014-17022) . Philippines. MUSORSTOM 3 Stn CP133, 11°58’N, 121°52’E, 334-390 m, 5.VI.1985, 4 ♂ 2.5-3.4 mm, 7 ov. ♀ 2.3-3.5 mm, 4 ♀ 2.1-2.7 mm (MNHN-IU-2014-17023) .

ETYMOLOGY„ From the Latin vicinus (near), alluding to a character of the close proximity of the the anterolateral and the orbital lateral spine of the carapace.

DISTRIBUTION„ New Caledonia, Loyalty Islands, Norfolk Ridge, and Philippines; 334- 504 m.

SIZE„ Males, 2.5-3.4 mm; females, 2.1-3.5 mm; ovigerous females from 2.3 mm.

DESCRIPTION„ Small species. Carapace: Broader than long (0.9 × as long as broad); greatest breadth 1.6 × distance between anterolateral spines. Dorsal surface smooth, with very sparse setae, slightly convex from anterior to posterior. Lateral margins straightly or slightly convexly divergent posteriorly, bearing 9 spines: first anterolateral, directly lateral to lateral orbital spine and reaching apex of that spine; second small, remote from first and close to third; third as large as first, situated at anterior end of anterior branchial region, dorsal to level of other spines, accompanying small spine dorsomesial to it; fourth small (obsolete on right side in holotype); fifth to ninth posteriorly diminishing, placed on posterior branchial region; fifth at anterior end of posterior branchial region, as large as third; ninth often obsolescent. Rostrum narrow triangular, with interior angle of 18-23°; ventral surface horizontal or slightly deflected ventrally; dorsal surface concave, lateral margin with subapical spine; length about half that of remaining carapace, breadth half carapace breadth at posterior carapace margin. Lateral orbital spine subequal to or very slightly smaller than closely subparalleling anterolateral spine. Pterygostomian flap with small spines arranged roughly in 2 rows, one in midline and another along anterior half of dorsal margin; anterior margin somewhat angular, produced to small spine.

Sternum: Excavated sternum with convex anterior margin, surface with obsolescent ridge in midline. Sternal plastron nearly as long as broad, lateral extremities slightly divergent posteriorly on sternites 4-5, subparallel on sternites 6-7. Sternite 3 shallowly depressed; anterior margin shallowly or moderately concave, medially with small V-shaped or deep narrow notch flanked by indistinct or very small spine discernible only under high magnification, anterolaterally sharp angular. Sternite 4 having anterolateral margin nearly straight or slightly convex, anteriorly ending in small spine; posterolateral margin about two-thirds length of anterolateral margin. Anterolateral margin of sternite 5 anteriorly convex, about as long as posterolateral margin of sternite 4.

Abdomen: Polished, sparingly setose. Somite 1 without transverse ridge. Somite 2 tergite 2.5-2.8 × broader than long; pleural lateral margin feebly concave and slightly divergent posteriorly, posterolaterally bluntly angular. Pleuron of somite 3 with bluntly angular lateral terminus. Telson half as long as broad; posterior plate as long as anterior plate, feebly emarginate on posterior margin.

Eye: Relatively short (1.6 × longer than broad), terminating in midlength of rostrum, distally somewhat narrowed. Cornea more than half length of remaining eyestalk.

Antennule and antenna: Ultimate article of antennular peduncle 2.5-3.2 × longer than high. Antennal peduncle overreaching cornea. Article 2 with strong distolateral spine. Antennal scale distally sharp, distinctly overreaching peduncle, occasionally with small spine on lateral proximal margin, breadth 1.8-2.0 × that of article 5. Distal 2 articles each with distomesial spine; article 5 1.5 × longer than article 4, breadth 0.5-0.6 × height of ultimate article of antennule. Flagellum consisting of 9-12 segments, not reaching distal end of P1 merus.

Mxp: Mxp1 with bases close to each other but not contiguous. Mxp3 basis without denticles on mesial ridge. Ischium with distally rounded flexor margin, crista dentata with very small or obsolescent denticles. Merus twice as long as ischium, well compressed mesio-laterally, somewhat concave on mesial face, bearing small or moderate-sized distolateral spine; flexor margin with 2 small, close spines distal to midlength, each accompanying long setae. Carpus with distolateral spine.

P1: 4.8-5.2 × longer than carapace, covered with fine setae. Ischium with moderate-sized dorsal spine, ventromesial margin with a few very small spines or tubercles, subterminal spine obsolescent. Merus 1.0-1.2 × longer than carapace, ventrally with 1 distomesial and 1 distolateral spine, and a few tubercles on proximal mesioventral surface. Carpus 1.0- 1.2 × length of merus, with mesial and lateral distoventral spines. Palm unarmed, 3.0-3.4 × (males) or 2.9-5.9 × (females) longer than broad, as long as or slightly longer than carpus. Fingers inclined slightly laterally, distally incurved, crossing when closed; movable finger 0.4-0.5 × as long as palm, opposable margin with median process fitting to between opposite 2 low processes on fixed finger when closed.

P2-4: Moderately setose, broad and well compressed mesio-laterally. Meri successively slightly shorter posteriorly (P3 merus often subequal to P2 merus, P4 merus 0.9 × length of P3 merus), equally broad on P2-4; length-breadth ratio, 2.8-3.4 on P2, 2.2-3.1 on P3, 2.1-3.0 on P4; dorsal margin with several very small spines on P2, a few small spines or eminences proximally on P3, nearly smooth on P4; ventrolateral margin with distal spine distinct on P2 and P3, obsolete on P4. P2 merus 0.7-0.8 × length of carapace, 1.0-1.1 × length of P2 propodus; P3 merus subequal to length of P3 propodus; P4 merus 0.8-0.9 × length of P4 propodus. Carpi subequal; shorter than dactyli (carpus-dactylus length ratio, 0.9-0.95 on P2, 0.7-0.9 on P3 and P4); carpus-propodus length ratio, 0.4-0.5 on P2, 0.4 on P3 and P4. Propodi shorter on P2 than on P3 and P4, subequal on P3 and P4; flexor margin slightly convex or straight, ending in pair of spines preceded by 5-6 spines somewhat distant from one another at most along distal two-thirds on P2 and P3, 4 spines on P4. Dactyli longer than carpi on P2-4 (dactylus-carpus length ratio, 1.1 on P2, 1.2-1.4 on P3 and P4); dactylus-propodus length ratio, 0.5-0.6 on P2-4; flexor margin nearly straight on P2, slightly curved on P3, more curved on P4, with 7-8 (rarely 6) loosely arranged spines, ultimate spine slender, remaining spines sharp subtriangular, obliquely directed, loosely arranged and proximally diminishing, penultimate more than 2 × broader than ultimate, subequal to or slightly broader than antepenultimate, proximal 1 or 2 much smaller, ultimate very close to penultimate.

Eggs. Eggs carried 1-9 in number; size, 0.88 mm × 0.94 mm - 1.15 mm × 1.25 mm.

PARASITES„ One of the males from MUSORSTOM 3 Stn CP133 (MNHN-IU-2014-17023) bears a rhizocephalan externa.

REMARKS„ Uroptychus vicinus strongly resembles U. beryx n. sp. in the spination of the carapace, especially the lateral orbital spine being slightly larger than or subequal to the anterolateral spine and in having a median notch on the anterior margin of sternite 3. However, they can be separated by the following differences: the last lateral marginal spine of the carapace in U. beryx is closer to the posterior end, rather than to the preceding spine as in U. vicinus ; the antennal scale is shorter in U. beryx , barely reaching instead of overreaching the distal end of article 5, and article 5 is unarmed instead of bearing a strong distomesial spine; and the P2-4 dactyli bear 9 or 10 closely arranged, perpendicularly directed spines proximal to the slender ultimate in U. beryx , 5-7 loosely arranged, obliquely directed spines in U. vicinus .

The characters listed below link the species to U. annae n. sp., U. multispinosus Ahyong & Poore, 2004 , U. perpendicularis n. sp., U. seductus n. sp., U. spinosior n. sp., and U. tridentatus ( Henderson, 1885) : the carapace lateral margin with a row

of spines, the rostrum with a subapical spine on each side, the pterygostomian flap with small spines on the surface, the antennal articles 4 and 5 each bearing a distomesial spine, the antennal scale overreaching article 5, the Mxp3 ischium rounded on the distal end of flexor margin, and the P2-4 dactyli with subtriangular flexor marginal spines.

Uroptychus annae , U. perpendicularis , U. spinosior and U. tridentatus are readily distinguished from the others by having the flexor marginal spines of P2-4 dactyli directed subperpendicularly instead of obliquely.

The lateral orbital spine is subequal to or slightly smaller than the anterolateral spine in U. vicinus and U. multispinosus , whereas in the other species it is much smaller. In U. vicinus , the anterolateral spine is situated directly lateral and very close to the lateral orbital spine, whereas it is distinctly posterior to and separated from that spine by its basal breadth in U. multispinosus . In addition, the lateral marginal spines of the carapace in U. vicinus are distinct rather than very small or obsolescent as in U. multispinosus , and an additional spine dorsomesial to the third spine is consistent in U. vicinus , absent in U. multispinosus . Uroptychus vicinus is distinguished from U. seductus by having a small dorsal spine mesial to the third carapace lateral spine, the P1 ischium bearing an obsolescent instead of strong subterminal spine on the ventromesial margin, the Mxp3 ischium lacking a spine near the rounded flexor distal margin. The last-mentioned spine is present in U. seductus , U. spinosior and U. tridentatus , absent in the other species. Uroptychus spinosior differs from U. vicinus in having more numerous spines on the carapace lateral margin and in having the anterolateral spine overreaching the much smaller lateral orbital spine.

Uroptychus perpendicularis has a small dorsal spine mesial to the third carapace lateral spine as in U. vicinus . It differs from U. vicinus , in addition to the arrangement of spines on the P2-4 dactyli (see above), in having the anterolateral spine of the carapace distinctly larger than instead of subequal to or slightly larger than the lateral orbital spine, and in having the antennal article 2 unarmed instead of bearing a strong distolateral spine.

Figures

FIGURE 278 Uroptychus vicinus n. sp.,holotype,male 3.3 mm (MNHN-IU-2014-17019).A, carapace and anterior part of abdomen,proximal part of right P1 included, dorsal. B, same, lateral.C, anterior part of sternal plastron, with excavated sternum and basal part of Mxp1. D, telson. E, left antenna,ventral.F, right Mxp3,setae omitted, ventral.G, left Mxp3,merus and carpus, lateral.H, right P1, proximal part, setae omitted,ventral.I, same, proximal part omitted, dorsal.Scale bars: 1 mm.

FIGURE 279 Uroptychus vicinus n. sp., holotype, male 3.3 mm (MNHN-IU-2014-17019). A, left P2, lateral. B, same, distal part, setae omitted, lateral.C, left P3, setae omitted, lateral. D, same,distal part, setae omitted,lateral. E, left P4,setae omitted, lateral. Scale bars:1 mm.