Uroptychus articulatus, 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 : 70-73

Uroptychus articulatus n. sp.

Figures 18 , 19

TYPE MATERIAL — Holotype: Vanuatu. MUSORSTOM 8 Stn DW1070, 15°37’S, 167°16’E, 184-190 m, 4.X.1994, 1 ov. ♀ 2.8 mm ( MNHN-IU-2013-8569 ) . Paratypes: New Caledonia. Loyalty Ridge. MUSORSTOM 6 Stn DW417, 20°14.80’S, 167°03.65’E, 283 m, with? Chrysogorgia sp. ( Calcaxonia , Chrysogorgiidae ), 16.IX.1989, 1 ♂ 2.3 mm ( MNHN- IU-2014-17314) . – Stn CP454, 21°00.60’S, 167°26.50’E, 260 m, 20.II.1989, 3 ♂ 1.8-2.2 mm, 2 ov. ♀ 2.0, 2.2 mm ( MNHN- IU-2013-8566) . New Caledonia. BATHUS 1 Stn CP669, 20°57.3’S, 165°35.3’E, 255-280 m, 14.III.1993, 1 ov. ♀ 2.3 mm (MNHN-IU-2014-17315) . Vanuatu. MUSORSTOM 8 Stn CP963, 20°20.10’S, 169°49.08’E, 400-440 m, 21.IX.1994, 1 ov. ♀ 3.2 mm (MNHN-IU-2014-17316) . – Stn DW967, 20°19.45’S, 169°52.87’E, 295-334 m, 21.IX.1994, 1 ov. ♀ 2.9 mm (MNHN-IU-2014-17317) . – Stn CP1017, 17°52.80’S, 168°26.20’E, 294-295 m, 27.IX.1994, 4 ♂ 2.3-3.1 mm, 2 ov. ♀ 3.0, 3.3 mm (MNHN-IU-2013-8567) . – Stn CP1018, 17°52.88’S, 168°25.08’E, 300-301 m, 27.IX.1994, 2 ov. ♀ 2.8, 3.2 mm, 1 ♀ 3.4 (with rhizocephalan parasite) (MNHN-IU-2014-17318) . – Stn CP1023, 17°47.60’S, 168°48.83’E, 321 m, 28.IX.1994, 2 ♂ 2.5, 3.1 mm (MNHN-IU-2013-12280 & MNHN-IU-2013-12281) . – Stn CP1024, 17°48.21’S, 168°38.77’E, 335-370 m, 28.IX.1994, 1 ov. ♀ 3.0 mm, 1 ♀ 3.3 mm (MNHN-IU-2013-12282 & MNHN-IU-2013-12283) .

ETYMOLOGY„ From the Latin articulatus (articulated), in reference to the articulated antennal scale, by which the species is differentiated from U. scandens .

DISTRIBUTION„ New Caledonia, Vanuatu and Loyalty Ridge, in 184- 334 m.

SIZE„ Males, 1.8-3.1 mm; females, 2.0- 3.4 mm; ovigerous females from 2.0 mm.

DESCRIPTION„ Small species. Carapace: Broader than long (0.8-0.9 × as long as broad); greatest breadth 1.4-1.6 × distance between anterolateral spines. Dorsal surface somewhat convex from anterior to posterior, setose on lateral portion and on epigastric region, with very small spines on epigastric, hepatic and anterior lateral branchial regions, those on hepatic region somewhat larger. Lateral margins feebly or barely concave between hepatic and branchial regions, convex along branchial region, with row of small spines; anterolateral spine larger than others, directed somewhat anterolaterally. Rostrum narrow triangular, directed straight forward, with interior angle of 25-30°; lateral margins slightly concave, with several obsolescent denticles; dorsal surface somewhat concave; length subequal to or slightly larger than (1.1 ×) breadth, 0.4 × that of remaining carapace, breadth about half carapace breadth measured at posterior carapace margin; lateral orbital spine very small, somewhat anterior to level of anterolateral spine. Pterygostomian flap anteriorly angular, produced to strong sharp spine followed by a few spines along dorsal margin anterior to linea anomurica and another few spines along ventral margin; surface with small spines on anterior half.

Sternum: Excavated sternum with slightly convex anterior margin; surface smooth, without ridge and central spine, with setae along anterior margin. Sternal plastron 0.8-0.9 × as long as broad; lateral extremities slightly convex, sternite 6 broadest. Sternite 3 slightly depressed in ventral view, anterior margin broadly and deeply excavated in subsemicircular shape, with pair of small median spines contiguous at base or separated by small notch, occasionally with a single median spine instead, laterally rounded or angular, occasionally with a few denticles. Sternite 4 having anterolateral margin feebly convex, anteriorly ending in anteriorly directed spine occasionally followed by a few small spines, posterolateral margin 0.8 × as long as anterolateral margin. Anterolateral margin of sternite 5 as long as posterior margin of sternite 4.

Abdomen. Somite 1 gently convex from anterior to posterior. Somite 2 tergite 2.4-2.7 × broader than long, pleuron slightly concavely divergent posteriorly, ending in rounded margin. Pleura of somites 3-5 laterally rounded. Telson half as long as broad; posterior plate with posterior margin slightly emarginate, concave or feebly convex, length 1.9-2.5 × that of anterior plate. Eyes: Elongate, 1.8-2.1 × longer than broad, falling short of apex of rostrum, distinctly broader proximally than distally, greatest breadth 1.2-1.3 × larger than that of cornea, lateral margin convex, mesial margin concave. Cornea slightly inflated, 0.4-0.5 × length of remaining eyestalk.

Antennule and antenna: Ultimate article of antennular peduncle 3.3-3.6 × longer than high. Antennal peduncle reaching apex of rostrum. Article 2 with strong distolateral spine reaching midlength of article 4. Antennal scale 1.2 × broader than article 5, terminating in or overreaching midlength of, and not reaching point two-thirds length of article 5, laterally with 0-2 spines. Articles 4 with distinct distomesial spine. Article 5 with very small, obsolescent distomesial spine, length 1.3-1.8 × that of article 4, breadth 0.5 × height of ultimate article of antennule. Flagellum of 8-11 segments reaching midlength to distal quarter of P1 merus, apical seta somewhat longer than flagellum, reaching or overreaching distal end of P1 merus.

Mxp: Mxp1 with bases broadly separated. Mxp3 with long setae. Basis with 1 or 2 distal denticles on mesial ridge. Ischium with small spine lateral to distal end of flexor margin, crista dentata with a few to several obsolescent denticles. Merus more than twice (2.3 ×) length of ischium, ridged along flexor margin; with 2-4 spines on distal third of flexor margin and 1 or 2 small distolateral spines. Carpus unarmed.

P1: Slender, subcylindrical, 6.6-7.4 × (males), 7.0-7.6 × (females) longer than carapace, bearing long setae. Ischium dorsally with basally broad, short, depressed spine accompanying much smaller spine laterally, unarmed ventromesially. Merus 1.5-1.6 × longer than carapace, bearing 2 rows of spines (mesial row of somewhat larger spines subparalleling another row of denticle-like, bifurcate spines directly dorsolateral to it). Carpus 1.3-1.5 × longer than merus, unarmed. Palm 4.1-5.0 × (males), 6.3-6.9 × (females) as long as broad, 0.8-0.9 × as long as carpus, very slightly broadened distally. Fingers relatively narrow distally, gaping in proximal third strongly in large males, slightly in females and small males; opposable margins fitting to each other when closed in distal two-thirds; movable finger 0.4 × (rarely 0.5 x) length of palm, with obtuse process (more pronounced in males than in females) at midpoint of gaping portion.

P2-4: With long setae like P1. Meri successively shorter posteriorly (P3 merus 0.8 × length of P2 merus, P4 merus 0.8-0.9 × length of P3 merus), slightly broader on P3 than on P2 and P4; length-breadth ratio, 4.5-5.0 on P2, 3.5-3.8 on P3, 3.1-3.4 on P4; dorsal margin with 4-8 small spines on proximal two-thirds on P2, 3-7 spines on P3, unarmed on P4; P2 merus 1.1-1.2 × length of carapace, 1.3-1.4 × length of P2 propodus; P3 merus 1.2 × length of P3 propodus; P4 merus 1.1 × length of P4 propodus. Carpi subequal on P3 and P4 and longer on P2 or successively shorter posteriorly; carpus-propodus length ratio, 0.5 on P2-P4. Propodi successively shorter posteriorly; flexor margin straight in lateral view, with pair of short, slender terminal spines only. Dactyli subequal in length on P2-4, shorter than carpus, dactyluscarpus length ratio, 0.6 on P2, 0.7 on P3 and P4; dactylus-propodus length ratio, 0.3 on P2-P4; truncate, bearing 6-8 slender spines obscured by setae, 3 of these located on terminal (distal) margin, remainder perpendicular to flexor margin, terminal spines somewhat smaller than flexor marginal spines.

Eggs. Number of eggs carried, 3-26; size, 0.58 × 0.63 mm - 0.63 × 0.81 mm.

REMARKS — The species is grouped together with Uroptychus scandens Benedict, 1902 , U. imparilis n. sp. and U. parisus n. sp., by having truncate P2-4 dactyli. Characters distinguishing these four species are very slight and are outlined under the account of U. scandens (see below).

The male from MUSORSTOM 6 Stn DW417 (MNHN-IU-2014-17314) was collected together with chrysogorgiid corals, but their commensal relationship cannot be assumed at present.

Figures

FIGURE 18 Uroptychus articulatus n. sp., holotype, ovigerous female 2.8 mm (MNHN-IU-2013-8569). A, carapace and anterior part of abdomen, dorsal. B, same, lateral. C, sternal plastron, with excavated sternum and basal parts of Mxp1. D, right pleura of abdominal somites 2-5, dorsolateral. E, telson. F, left antenna, ventral. G, right Mxp3,ventral. H, same,setae omitted. I, same, lateral. Scale bars: 1 mm.

FIGURE 19 Uroptychus articulatus n. sp., holotype,ovigerous female 2.8 mm (MNHN-IU-2013-8569).A, right P1, dorsal. B, same,proximal part, ventral. C, left P2, lateral. D, same, distal part, setae omitted, lateral. E, left P3, setae omitted, lateral. F, same, distal part. G, left P4, lateral. H, same,distal part,lateral.Scale bars:1 mm.