Uroptychus ctenodes, 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 : 148-151

Uroptychus ctenodes n. sp.

Figures 59 , 60

TYPE MATERIAL — Holotype: Indonesia, Tanimbar Islands . KARUBAR Stn CP 45, 7°54’S, 132°47’E, 302-305 m, 29.X.1991, ov. ♀ 4.6 mm ( MNHN-IU-2014-16369 ).

ETYMOLOGY„ From the Greek ktenodes (comb-like), alluding to a comb-like arrangement of spines on the lateral margin of the carapace and pterygostomian flap, characteristic of the species.

DISTRIBUTION„ Tanimbar Islands, Indonesia; 302- 305 m.

DESCRIPTION„ Small species. Carapace: Strongly broadened posteriorly, 1.7 × broader than long (0.6 × as long as broad); greatest breadth 2.1 × distance between anterolateral spines. Dorsal surface convex on gastric and cardiac regions, covered with very fine short setae discernible under high magnification; posterior half laterally crested. Lateral margins nearly straight and strongly divergent posteriorly in anterior half; anterolateral spine strong, extending forward to level of rostral tip; posterior half convexly convergent posteriorly, with row of 7 or 8 strong blunt spines, all anterolaterally directed. Rostrum broad triangular, as long as broad, with interior angle of 73°, horizontal, flattish on dorsal surface, not reaching distal end of eye; length 0.2 × that of remaining carapace, breadth less than half carapace breadth measured at posterior carapace margin. Lateral limit of orbit rounded, not angular, directly leading to anterolateral spine. Pterygostomian flap low in posterior half (posterior half about 0.3 × as high as anterior half), anteriorly somewhat angular, produced to small but distinct spine; surface with row of 5 or 6 strong blunt spines arranged along lower margin: in dorsal view, this row in line with carapace lateral spines representing comb-like arrangement.

Sternum: Excavated sternum with anterior margin nearly transverse between bases of Mxp1, surface strongly excavated, without median ridge and central spine. Sternal plastron strongly depressed posteriorly in ventral view, setose laterally; lateral margins of somites 4-6 strongly divergent. Sternite 3 shallowly depressed; anterior margin deeply excavated, representing semicircular shape, without median notch and submedian spines, laterally rounded. Sternite 4 with convex anterolateral margin, posterolateral lobe not pronounced. Anterolateral margins of sternite 5 convex and strongly divergent posteriorly, length much more than that of posterolateral margin of sternite 4.

Abdomen: Smooth, covered with short fine setae. Somite 1 smoothly convex from anterior to posterior, without elevated transverse ridge. Somite 2 tergite 3.1 × broader than long; pleuron anterolaterally rounded, posterolaterally tapering, lateral margin concave and strongly divergent posterolaterally. Pleuron of somites 3 also tapering. Telson 0.4 × as long as broad, posterior plate feebly concave on posterior margin, length 1.2 × that of anterior plate.

Eye: Elongate, 2 × longer than broad, with lateral and mesial margins subparallel. Cornea not dilated, length about half that of remaining eyestalk.

Antennule and antenna: Ultimate article of antennular peduncle 2.8 × longer than high. Antennal peduncle extending far beyond eye. Article 2 with stout distolateral spine. Antennal scale slightly more than half as broad as article 5, slightly overreaching midlength of article 4. Articles 4 and 5 unarmed, with soft fine setae on distal portion; article 5 1.8 × longer than article 4, breadth 0.9 × height of antennular ultimate article. Flagellum consisting of 5 segments, very short, nearly as long as article 5.

Mxp: Mxp1 with bases broadly separated. Mxp3 with relatively long soft setae particularly on lateral surface of merus and distal part of lateral surface of ischium. Coxa ventrolaterally produced to blunt, depressed process. Basis without denticles on mesial ridge. Ischium with about 30 small denticles on crista dentata; flexor margin not rounded distally. Merus 2.2 × longer than ischium, flexor margin not cristate but roundly ridged. Carpus unarmed.

P1: 4 × longer than carapace; tubercle-like spines on proximal mesial portion of merus and along ventromesial margin of ischium. Ischium with small blunt dorsal spine, unarmed ventrally and ventromesially. All articles with short fine setae thick along mesial margin. Merus 0.8 × length of carapace. Carpus 1.5 × longer than merus. Palm 3.4 × longer than broad, 1.2 × longer than carpus. Fingers directed anterolaterally, relatively broad and moderately depressed; movable finger distally incurved, length 0.4 × that of palm, opposable margin with triangular (dorsal view) median process; opposable margin of fixed finger with eminence distal to position of opposite process on movable finger.

P2-4: P2-P3 relatively thick mesio-laterally, with soft fine setae. P4 missing. Meri slightly shorter on P3 than on P2, subequal in breadth on P2 and P3, length-breadth ration, 3.0 on P2, 2.8 on P3; dorsal margin proximally with 2 small tubercle-like spines only discernible under high magnification; P2 merus 0.6 × length of carapace, slightly longer than P2 propodus; P3 merus as long as P3 propodus. Carpi subequal in length on P2 and P3, slightly less than half length of propodi (carpus-propodus length ratio, 0.45 on P2, 0.43 on P3), nearly as long as dactyli on P2 and P3. Propodi somewhat longer on P3 than on P2; flexor margin unarmed. Dactyli slightly longer on P3 than on P2, with straight flexor margin ending in strong spine preceded by 6 loosely arranged, sharp, proximally diminishing spines nearly perpendicular to margin (proximal-most spine obliquely directed), proximal spines obscured by setae.

Eggs. Eggs carried 22 in number; size, 1.16 mm in diameter.

REMARKS — The species is unique in Uroptychus in the following particulars: the anterolateral spine is extremely strong, situated directly lateral to the unarmed lateral limit of the orbit; the dorsal surface of the carapace is crested laterally in the posterior half; the antenna bears a very small antennal scale much narrower than article 5 and a very short, fivesegmented flagellum as long as article 5, and the pterygostomian flap is very low in the posterior half and bears a row of spines that is, when viewed dorsally, continued on to the row of lateral carapace spines. This species could be placed in a different genus but it stays in Uroptychus awaiting a discovery of additional material that allows molecular analyses.

Figures

FIGURE 59 Uroptychus ctenodes n. sp., holotype,ovigerous female 4.6 mm (MNHN-IU-2014-16369).A, carapace and anterior part of abdomen,fine setae omitted,dorsal.B, same,fine setae on right side omitted,anterior.C, same,dorsal part omitted,lateral.D, anterior part of sternal plastron,with excavated sternum and basal parts of Mxp1. E, telson. F, right antenna,ventral. G, left Mxp3, ventral.Scale bars:1 mm.

FIGURE 60 Uroptychus ctenodes n. sp., holotype, ovigerous female 4.6 mm (MNHN-IU-2014-16369). A, right P1, dorsal. B, right P2, lateral. C, same, distal part,setae omitted, lateral. D, right P3, setae omitted,lateral.Scale bars:1 mm.