Uroptychus plautus, 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 : 401-403

Uroptychus plautus n. sp.

Figures 197 , 198

TYPE MATERIAL — Holotype: Indonesia, Kai Islands . KARUBAR Stn CC 10, 5°21’S, 132°30’E, 329-389 m, with coral Primnoidae (Calcaxonia) , 23.X.1991, ov. ♀ 6.8 mm ( MNHN-IU-2014-16861 ).

ETYMOLOGY„ From the Latin plautus (broad), alluding to the broad rostrum and broad sternal plastron of the species.

DISTRIBUTION„ Kai Islands, Indonesia; in 329- 389 m.

DESCRIPTION„ Medium-sized species. Carapace: 1.2 × broader than long (0.85 × as long as broad); greatest breadth 2.0 × distance between anterolateral spines. Dorsal surface finely granulate (discernible under high magnification), sparingly with short soft setae, anteriorly elevated from level of rostrum in profile, bearing depression between gastric and cardiac regions. Lateral margins convexly divergent, somewhat ridged along posterior portion; anterolateral corner angular, ending in very tiny spine not reaching lateral orbital angle. Rostrum broader than long, distally blunt triangular, with interior angle of 42°; dorsal surface horizontal, somewhat concave; length 0.3 × that of remaining carapace, breadth half carapace breadth at posterior carapace margin. Lateral limit of orbit acuminate, slightly anterior and relatively close to anterolateral spine. Pterygostomian flap anteriorly roundish, without distinct spine.

Sternum: Excavated sternum with anterior margin broad, blunt triangular, surface ridged in midline. Sternal plastron 1.5 × as broad as long, lateral extremities convexly divergent posteriorly. Sternite 3 shallowly depressed, anterior margin moderately concave with small median notch lacking flanking spine, laterally rounded. Sternite 4 short relative to breadth; anterolateral margin anteriorly rounded, length 1.3 × that of posterolateral margin. Anterolateral margin of sternite 5 1.2 × longer than posterolateral margin of sternite 4.

Abdomen: Sparsely setose; Somites long relative to breadth. Somite 1 dorsally convex from anterior to posterior. Somite 2 tergite 2.1 × broader than long; pleural lateral margin somewhat concavely divergent posteriorly, with blunt posterolateral terminus. Pleuron of somite 3 laterally blunt. Telson half as long as broad; posterior plate slightly longer than anterior plate, posterior margin distinctly emarginate.

Eye: Relatively small, elongate (2.2 × longer than broad), slightly broadened proximally, slightly overreaching midlength of rostrum. Cornea slightly dilated, about half as long as remaining eyestalk.

Antennule and antenna: Ultimate article of antennule 3.8 × longer than high. Antennal peduncle overreaching cornea, not reaching apex of rostrum. Article 2 distolaterally angular and acuminate. Antennal scale 2.0 × broader than article 5, slightly falling short of midlength of article 5. Distal 2 articles unarmed. Article 5 1.5 × longer than article 4, breadth 0.8 × height of antennular ultimate article. Flagellum consisting of 10 segments, slightly falling short of distal end of P1 merus.

Mxp: Mxp1 with bases broadly separated. Mxp3 setose. Basis without denticles on mesial ridge. Ischium with about 30 distally diminishing denticles on crista dentata, flexor margin distally not rounded. Merus 2.2 × longer than ischium, relatively thick, unarmed, flexor margin roundly ridged. Carpus unarmed.

P1: Left P1 missing. Right P1 short, not massive, 3.5 × longer than carapace; sparingly with soft fine setae, spineless except for ischium. Ischium with short, basally broad, depressed dorsal spine, ventrally unarmed. Merus 0.85 × length of carapace. Carpus 1.1 × length of merus. Palm 4.0 × longer than broad, as long as carpus. Fingers not gaping, each ending in small incurved spine; fixed finger feebly sinuous; movable finger slightly less than half length of palm; opposable margin with 2 low processes, proximal one fitting to longitudinal groove on opposite face of fixed finger.

P2-4: Left P2 and right P3 missing. Relatively thick, not compressed mesio-laterally, setose like P1. Meri successively shorter posteriorly (P3 merus 0.96 × length of P2 merus, P4 merus 0.90 × length of P3 merus), equally broad on P2-4; length-breadth ratio, 4.5 on P2, 4.3 on P3, 3.8-3.9 on P4; unarmed; P2 merus 0.8 × length of carapace, slightly (1.06 x) longer than P2 propodus; P3 merus as long as P3 propodus; P4 merus 0.9 × length of P4 propodus. Carpi successively slightly shorter posteriorly, 1.3 × longer than dactyli on P2-4; carpus-propodus length ratio, 0.40 on P2, 0.36 on P3, 0.31 on P4. Propodi slightly shorter on P2 than on P3 and P4; flexor margin nearly straight, with pair of very tiny, vestigial terminal spines only. Dactyli subequal, slightly curving, 0.8 × as long as carpi and 0.3 × as long as propodi on P2-4, bearing 2 distal spines, terminal one shorter and more slender than subterminal spine.

Eggs. Number of eggs carried, 4; size, 1.5 × 1.7 mm.

REMARKS — The P2-4 dactyli bearing only two terminal spines are very unusual in the species of Uroptychus but possessed by U. pilosus Baba, 1981 , U. inaequalis n. sp. (see above) and U. plautus n. sp. Uroptychus plautus is distinguished from U. pilosus by the rostrum that is much broader, with the interior angle of 42° instead of 23°; the anterolateral corner of the carapace is distinctly angular instead of roundish; the dorsal margins of P2-4 meri are unarmed instead of bearing a row of small spines at least on the proximal portion; the pterygostomian flap is anteriorly roundish instead of angular bearing a sharp spine; the antennal article 2 is distolaterally angular and acuminate instead of bearing a distinct spine; and the ultimate spine on the P2-4 dactyli is smaller than instead of subequal to the penultimate spine. The new species is differentiated from U. inaequalis by the following particulars: the P2-4 dactyli are shorter instead of longer than carpi; the P4 merus is 0.90 instead of 0.75 times length of P4 propodus; the Mxp3 merus is unarmed instead of bearing distolateral and flexor marginal spines; the pterygostomian flap is anteriorly roundish instead of produced to a distinct spine; the antennal article 2 is distolaterally acuminate instead of bearing a strong spine; the anterolateral corner of carapace is angular instead of roundish; and the sternal plastron is 1.5 times broader than instead of as broad as long.

Figures

FIGURE 197 Uroptychus plautus n. sp., holotype, ovigerous female 6.8 mm (MNHN-IU-2014-16861). A, carapace and anterior part of abdomen, dorsal. B, same,lateral.C, anterior part of carapace,dorsal.D, excavated sternum and basal parts of Mxp1.E, anterior part of sternal plastron.F, telson. G, left antenna,ventral.H, left Mxp3, ventral.I, same,lateral.J, right P1, dorsal.K, same, fingers,setae omitted,ventral.Scale bars: 1 mm.

FIGURE 198 Uroptychus plautus n. sp., holotype, ovigerous female 6.8 mm (MNHN-IU-2014-16861). A, right P2, lateral. B, same, distal part, lateral.C, left P3, setae omitted,lateral.Scale bars:1 mm.