Uroptychus elongatus, 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 : 197-200

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Uroptychus elongatus

n. sp.

Uroptychus elongatus n. sp.

Figures 86 View FIGURE 86 , 87 View FIGURE 87 , 305D View FIGURE 305

TYPE MATERIAL — Holotype: Vanuatu. MUSORSTOM 8 Stn CP 1027, 17°53.05’S, 168°39.35’E, 550-571 m, 28.IX.1994, ov. ♀ 4.3 mm ( MNHN-IU-2014-16440 ) GoogleMaps . Paratypes: Vanuatu. MUSORSTOM 8 Stn CP1026, 17°50.35’S, 168°39.33’E, 437-504 m, 28.IX.1994, 2 ♂ 4.6, 5.0 mm, 1 ov. ♀ 4.8 mm, 1 ♀ 5.4 mm (MNHN-IU-2014-16441).

ETYMOLOGY„ From the Latin elongatus (prolonged), referring to elongate eyes, one of the characteristic features of the new species.

DISTRIBUTION„ Vanuatu; in 437- 571 m.

SIZE„ Males, 4.6-5.0 mm; females, 4.3-5.4 mm; ovigerous females from 4.3 mm.

DESCRIPTION„ Small species. Carapace: 0.9 × as long as broad; greatest breadth 1.7 × distance between anterolateral spines. Dorsal surface well convex from anterior to posterior, without distinct depression or groove, smooth, sparsely or barely setose along lateral margin. Lateral margins somewhat convex and slightly or moderately divergent posteriorly, bearing 6 or 7 spines: first anterolateral, relatively stout, overreaching much smaller lateral orbital spine, subequal to third and fourth; second very small, located on hepatic margin; remaining spines on branchial region posteriorly diminishing; sixth followed by eminence or additional small spine and ridge leading to posterior end of margin. Rostrum sharp triangular, with interior angle of 32-35°, nearly horizontal, dorsally excavated; length about one-third that of remaining carapace, breadth less than half carapace breadth measured at posterior carapace margin. Lateral orbital spine situated slightly anterior to level of anterolateral spine, separated from anterolateral spine by basal breadth of that spine. Pterygostomian flap high relative to length, anteriorly angular, produced to small sharp spine; tubercle-like small processes occasionally obsolescent on anterior half of surface.

Sternum: Excavated sternum strongly produced anteriorly between bases of Mxp1, ending in blunt tip, surface with ridge in midline. Sternal plastron slightly broader than long, lateral extremities somewhat divergent posteriorly. Sternite 3 well depressed; anterior margin weakly concave, with subovate or narrow deep median notch flanked by incurved spine, laterally sharp angular. Sternite 4 with anterolateral margin nearly straight, anteriorly ending in small spine usually accompanying 2 smaller spines lateral and mesial to it; posterolateral margin 0.7 × length of anterolateral margin.

Abdomen: With sparse or moderately dense setae. Somite 1 gently convex from anterior to posterior, without transverse ridge. Somite 2 tergite 2.3 × broader than long; pleural lateral margin concavely divergent posteriorly, posterolaterally rounded. Telson half as long as broad; posterior plate 1.3 × longer than anterior plate, posterior margin feebly emarginate or weakly concave.

Eye: Elongate, 2.0-2.2 × longer than broad, reaching or slightly overreaching rostral tip, slightly broadened proximally. Cornea not dilated, half as long as remaining eyestalk.

Antennule and antenna: Ultimate article of antennular article slightly more than 3 × longer than high. Antennal peduncle reaching rostral tip. Article 2 with small lateral spine. Antennal scale reaching distal end of article 5, breadth 1.7 × that of article 5. Article 4 with distomesial spine. Article 5 unarmed, length 1.5 × that of article 4, breadth slightly more than half height of ultimate antennular article. Flagellum consisting of 15-17 segments, slightly falling short of distal end of P 1 merus.

Mxp: Mxp1 with bases separated. Mxp3 with tufts of setae on lateral surfaces of ischium and merus. Basis with obsolescent distal denticle or unarmed on mesial ridge. Ischium thick, flexor margin distally rounded, crista dentata with row of very small denticles. Merus 1.8 × longer than ischium, concavely smooth on mesial face, bearing distinct distolateral spine and 1 or 2 obsolescent spines at point one-third from distal end of sharply ridged flexor margin. Carpus unarmed.

Pereopods sparingly with long, distally softened setae.

P 1: Relatively slender and subcylindrical, palm somewhat massive especially in males; length 4.7-6.0 × postorbital carapace length. Ischium dorsally bearing strong distal spine, ventromesially well-developed subterminal spine proximally followed by row of tubercle-like spines. Merus 1.1-1.2 × longer than carapace, ventrally bearing well-developed distomesial spine and a few small spines on mesioproximal portion. Carpus 1.2-1.4 × longer than merus, with small ventral distomesial and distolateral spines. Palm 2.9 × (male; missing in another male) or 3.4-4.2 × (females) longer than broad, as long as carpus. Fingers slightly incurved distally, slightly gaping in males, not gaping in females; opposable margin of fixed finger sinuous, that of movable finger with proximal blunt process fitting to longitudinal groove on opposite margin of fixed finger when closed; movable finger 0.4-0.5 × length of palm.

P 2-4: Moderately compressed mesio-laterally. Meri and carpi unarmed. Meri successively shorter posteriorly ( P 3 merus 0.8-0.9 × length of P 2 merus, P 4 merus 0.8-0.9 × length of P 3 merus), equally broad on P 2-4; length-breadth ratio, 3.8-4.2 on P 2, 3.6-3.8 on P 3, 3.0-3.2 on P 4; P 2 merus 0.9 × length of carapace, 1.2 × length of P 2 propodus; P 3 merus 0.9 × length of P 3 propodus; P 4 merus 0.7-0.8 × length of P 4 propodus. Carpi successively slightly shorter posteriorly ( P 3 carpus 0.9 × length of P 2 carpus, P 4 carpus 0.9 × length of P 3 carpus), slightly shorter than dactyli; length 0.5 × that of propodus on P 2, 0.4 × on P 3 and P 4. Propodi subequal on P 2-4 or successively slightly shorter posteriorly; flexor margin straight, ending in pair of spines preceded by row of 6-8 spines on distal two-thirds on P 2 and P 3, 4 spines on distal half on P 4. Dactyli somewhat curving, ending in slender spine preceded by 9-11 sharp, somewhat oblique, loosely arranged spines, ultimate more slender and shorter than antepenultimate, penultimate broader than antepenultimate; dactylus-propodus length ratio, 0.4 on P 2, 0.4-0.5 on P 3 and P 4.

Eggs. Number of eggs carried, 4-19; size, 1.13 mm × 1.03 mm to 1.30 mm × 1.25 mm.

Color. Holotype, MNHN-IU-2014-16440: Base color pale brown, carapace, P 1 and P 4 darker, abdomen translucent.

REMARKS — The elongate eyestalks and the spination of the carapace and P 2-4 are similar in U. elongatus , U. baeomma n. sp. (see above) and U. exilis n. sp. (see below). Uroptychus elongatus is distinguished from U. baeomma by the P 1 ischium that has a well-developed instead of obsolete subterminal spine on the ventromesial margin; and the P 3 merus is shorter than instead of subequal to the P 2 merus. The relationships with U. exilis is discussed under the remarks of that species (see below).

The elongate eyestalks and the spination of the P 2-4 dactyli as displayed by this species are also possessed by U. denticulisquama n. sp. (see above). However, U. elongatus is easily distinguished from that species by having a row of distinct spines instead denticles on the carapace lateral margin; the antennal scale is laterally unarmed instead of bearing small spines; and the P 2 merus is unarmed along the ventromesial margin instead of bearing a row of small spines.