Uroptychus perpendicularis, 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 : 392-394

Uroptychus perpendicularis n. sp.

Figure 194

TYPE MATERIAL — Holotype: New Caledonia, Norfolk Ridge. NORFOLK 2, Stn DW 2052, 23°42.29’S, 168°15.27’E, 473- 525 m, 24.X.2003, ♂ 3.0 mm ( MNHN-IU-2014-16855 ).

ETYMOLOGY„ From the Latin perpendicularis (upright, perpendicular), referring to spines on the P2-4 dactyli that are perpendicular to the flexor margin in the new species.

DISTRIBUTION„ Norfolk Ridge; 473- 525 m.

DESCRIPTION„ Carapace: Slightly broader than long (0.93 × as long as broad); greatest breadth 1.6 × distance between anterolateral spines. Dorsal surface feebly convex from anterior to posterior, bearing very sparse short setae. Lateral margins convex on posterior branchial regions, bearing 7 or 8 spines; anterolateral (first) spine well developed, distinctly larger than and slightly overreaching lateral orbital spine, other 6 or 7 spines small; second spine on hepatic margin, ventral to level of first and third; third spine located on anterior end of branchial margin, accompanying small spine dorsomesial to it; remaining 5 spines on posterior branchial margin; 1 or 2 small hepatic spines mesial to between first and second spines (or directly behind anterolateral spine). Rostrum narrow triangular, with interior angle of 20°, nearly horizontal, length more than half that of remaining carapace, breadth half carapace breadth at posterior carapace margin; lateral margin with small subterminal spine; dorsal surface concave. Pterygostomian flap anteriorly angular, produced to sharp spine, surface with row of spines directly below anterior part of linea anomurica.

Sternum: Excavated sternum anteriorly produced between bases of Mxp1, bearing weak ridge in midline. Sternal plastron slightly broader than long, lateral extremities between sternites 4-7 gently divergent posteriorly. Sternite 3 weakly depressed; anterior margin concavely excavated, with small median notch without flanking spine, laterally rounded. Sternite 4 having anterolateral margin anteriorly angular (right) or ending in small blunt spine (left), twice as long as posterolateral margin. Sternite 5 with anterolateral margin anteriorly convex, 1.3 × longer than posterolateral margin of sternite 4.

Abdomen: Smooth, nearly glabrous. Somite 1 without transverse ridge. Somite 2 tergite 3.0 × broader than long; pleural lateral margin somewhat concavely divergent posteriorly, anterior and posterior ends rounded. Pleuron of somite 3 laterally blunt. Telson half as long as broad; posterior plate slightly convex on posterior margin, length 1.4 × that of anterior plate.

Eye: Elongate (twice as long as broad), slightly overreaching midlength of rostrum; lateral and mesial margins subparallel. Cornea not dilated, about half length of remaining eyestalk.

Antennule and antenna: Ultimate article of antennular peduncle 3.1 × longer than high. Antennal peduncle somewhat overreaching cornea. Article 2 unarmed. Antennal scale overreaching peduncle, terminating at tip of strong distomesial spine of article 5, breadth 1.5 × that of article 5. Distal 2 articles each with strong distomesial spine; article 4 very slightly longer than article 4, breadth 0.6 × height of antennular ultimate article. Flagellum consisting of 11-12 segments, not reaching distal end of P1 merus.

Mxp: Mxp1 close to each other. Mxp3 with sparse short setae other than brushes on distal articles. Basis lacking denticles on mesial ridge. Ischium with distally rounded flexor margin; crista dentata with more than 20 denticles. Merus 2.5 × longer than ischium, flattish on mesial face; flexor margin sharply ridged, with 2 small spines about at distal quarter; distolateral spine strong. Carpus with distolateral spine and 1 distinct spine on proximal part of extensor margin.

P1: Missing.

P2-4: Compressed mesio-laterally, relatively broad. Meri subequal in length on P2 and P3, P4 merus 0.9 × length of P3 merus; length-breadth ratio, 3.6 on P2, 3.1 on P3 and P4; dorsal margin with row of very small spines distinct on P2 and P3, obsolete on P4; P2 merus 0.8 × length of carapace, 1.2 × length of P2 propodus; P3 merus as long as P3 propodus; P4 merus 0.9 × length of P4 propodus. Carpi subequal in length on P2 and P3, P4 carpus 0.9 × length of P3 carpus; carpus-propodus length ratio, 0.50 on P2, 0.46 on P3, 0.43 on P4; extensor margin with row of small spines on P2 only. Propodi subequal in length on P3 and P4, shorter on P2, flexor margin with pair of terminal spines preceded by 6 spines on P2, 5 spines on P3, 3 or 4 spines on P4. Dactyli subequal on P3 and P4, shorter on P2; as long as carpi on P2, slightly longer on P3 and P4; half as long as propodi on P2, slightly more than so on P3 and P4; flexor margin feebly curving, ending in slender spine preceded by 9 strong, long triangular spines perpendicular to margin, close to one another and successively diminishing proximally.

REMARKS — Uroptychus perpendicularis resembles U. multispinosus Ahyong & Poore, 2009 (see above) in having the carapace lateral margin with small spines, the rostrum with a subapical spine on each side, elongate eyes, the antennal peduncle with a strong spine on each of articles 4 and 5, and the antennal scale overreaching the peduncle. In U. perpendicularis , however, the anterolateral spine of the carapace is distinctly larger than instead of subequal to the lateral orbital spine; the antennal article 2 is unarmed instead of bearing a distinct distolateral spine; and the flexor marginal spines of the P2-4 dactyli are perpendicular to the margin rather than obliquely directed, and more numerous (10 versus 7) and closer to one another.

Uroptychus perpendicularis also resembles U. vicinus n. sp. Their relationships are discussed under the remarks of that species (see below).

The combination of the following characters links the species to U. lanatus n. sp.: the carapace with small lateral spines, the P2-4 propodi with a row of spines proximal to the pair of terminal spines, and the P2-4 dactyli with the ultimate of the flexor marginal spines more slender than the antepenultimate. These species can be distinguished by the following differences: the flexor marginal spines of the P2-4 dactyli in U. perpendicularis are subperpendicularly directed, whereas these are obliquely directed in U. lanatus ; the rostrum in U. perpendicularis bears a subapical spine on each side, which spine is absent in U. lanatus ; the antennal articles 4 and 5 in U. perpendicularis each bear a strong distomesial spine instead of being unarmed; and the P2-3 meri bear a row of dorsal spines instead of being spineless.

Figures

FIGURE 194 Uroptychus perpendicularis n. sp., holotype, male 3.0 mm (MNHN-IU-2014-16855). A, carapace and anterior part of abdomen, dorsal. B, same, lateral. C, sternal plastron, with excavated sternum and basal parts of Mxp1. D, telson. E, right antenna, ventral. F, right Mxp3, ventral. G, same, lateral. H, right P2, lateral. I, same, distal part, setae omitted, lateral.J, right P3, setae omitted, lateral. K, right P4, setae omitted, lateral. Scale bars: 1 mm.