Uroptychus setifer, 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 : 473-477

Uroptychus setifer n. sp.

Figures 237 , 238 , 306C

Uroptychus sp. — Kawamoto & Okuno 2003: 98, unnumbered fig.; 2006: 98, unnumbered fig.

TYPE MATERIAL — Holotype: Vanuatu. SANTO Stn NB12, 15°33.1’S, 167°09.6’E, 20 m, 19.IX.2006, ov. ♀ 2.2 mm ( MNHN-IU-2010-5436 ) . Paratypes: Japan. Kume-jima, Ryukyu Islands, 35 m, with Scuba, associated with coral, 27. VI.2001, T. Kawamoto coll., 1 ♂ 3.2 mm ( CMNH-ZC 00620) , 1 ♂ 3.2 mm ( CMNH-ZC 02157).

ETYMOLOGY„ From the Latin seta (bristle, seta) and fer (the suffix meaning bear), referring to long setae on the body and pereopods. When alive, the setae are whitish.

DISTRIBUTION„ Vanuatu and Japan (Ryukyu Islands); 12- 35 m.

DESCRIPTION„ Small species. Carapace: About as long as broad; greatest breadth 1.6 × distance between anterolateral spines. Dorsal surface sparingly with long setae, moderately convex from anterior to posterior, cardiac region more convex; with weak (holotype) or distinct (paratypes) depression between gastric and cardiac regions; 6 dorsal spines: 3 in transverse row on epigastric region, followed by 2 placed side by side on mesogastric region, and 1 on cardiac region; 2 small spines each on mesial part of posterior branchial region distinct (holotype and larger male paratype) or absent (smaller male paratype). Lateral margins convexly (holotype) or nearly straight (paratypes) divergent, with 6 spines; first anterolateral, moderate in size, overreaching lateral orbital spine; second relatively remote from first (with 1 or 2 much smaller spines between, in paratypes), situated on anterior end of anterior branchial margin, distinctly posterior to level of epigastric spines; third to sixth situated on posterior branchial region and slightly dorsomesial to margin; last situated at posterior quarter of posterior branchial margin, followed by ridge. Rostrum narrow triangular, with interior angle of 22-23,° nearly horizontal; dorsal surface moderately concave, length 0.47 (paratypes)-0.53 × (holotype) that of carapace, breadth half carapace breadth at posterior carapace margin. Lateral limit of orbit with tiny spine, directly mesial to anterolateral margin. Pterygostomian flap smooth on surface, with small spine on roundish anterior margin.

Sternum: Excavated sternum with convex anterior margin, surface smooth, without ridge. Sternal plastron 0.8 × as long as broad, lateral extremities divergent posteriorly. Sternite 3 well depressed, anterior margin shallowly excavated, with V-shaped median notch separating obsolescent submedian spines; anterolaterally angular. Sternite 4 with anterolateral margin relatively short, bearing 2 spines, anterior spine at anterior end and smaller than posterior spine situated slightly anterior to midlength, posterolateral margin as long as anterolateral margin. Sternite 5 slightly shorter than sternite 4; anterolateral margin feebly convex, moderately divergent posteriorly, length 1.4-1.5 × that of posterolateral margin of sternite 4.

Abdomen: Smooth, sparsely with tufts of a few to several long setae. Somite 1 gently convex from anterior to posterior, without distinct ridge. Somite 2 tergite 2.1 × broader than long; pleuron tapering, with lateral margin concavely strongly divergent posteriorly. Pleuron of somite 3 bluntly angular on posterolateral terminus. Telson half as long as broad; posterior plate 1.2 × longer than anterior plate, weakly concave on posterior margin.

Eye: Elongate, twice as long as broad, distally narrowed, slightly falling short of rostral tip. Cornea 0.3 × as long as remaining eyestalk.

Antennule and antenna: Ultimate article of antennule 4.5 × longer than high. Antennal peduncle reaching apex of rostrum. Article 2 unarmed. Antennal scale slightly broader than article 5, ending in midlength of that article. Articles 4 and 5 each with distomesial spine; article 5 1.5 × (holotype)-1.9 × (paratypes) longer than article 4, breadth 0.7 × height of ultimate article of antennule. Flagellum consisting of 7 or 8 (holotype)-10 (paratypes) segments, far falling short of distal end of P1 merus.

Mxp: Mxp1 with bases separated from each other. Mxp3 slender, with sparse long setae laterally. Basis without denticles on mesial ridge. Ischium with distinct spine lateral to distal end of flexor margin; crista dentata with obsolescent denticles; flexor margin not rounded distally. Merus 1.5 × longer than ischium, narrow relative to length, with distolateral and median flexor marginal spine. Carpus also with distolateral spine.

P1: 6.6 × longer than carapace, slender, with tufts of long setae. Ischium with sharp dorsal spine, ventromesially with subterminal spine. Merus 1.5 (holotype)-1.6 × (paratypes) longer than carapace; 4 rows of spines (more numerous in male paratypes) each continued on to carpus. Carpus 1.3 × longer than merus, as high as broad. Palm 5.0 × (holotype) or 3.1- 3.4 × (paratypes) longer than broad; mesial margin smooth (holotype) or cristate with 8 or 9 spines (paratypes), lateral margin smooth (holotype) or with obsolescent spines (paratypes); length 1.1-1.2 × that of carpus. Fingers not gaping, distally incurved, crossing when closed; movable finger 0.3 × length of palm, opposable margin with subtriangular blunt median process proximal to opposite eminence on fixed finger.

P2-4: Slender, somewhat compressed mesio-laterally, setose like P1. Ischium with small dorsal spine. Meri successively shorter posteriorly (P3 merus 0.9 × length of P2 merus, P4 merus 0.8 or 0.9 × length of P3 merus); breadths subequal on P2-4; small distal spine on dorsal and ventrolateral margins on P2-3, distodorsal spine obsolete on P4; small denticle-like spine at proximal quarter of dorsal margin on P2 and P3, obsolete on P4. P2 merus 1.2 × (holotype) or 1.6 × (paratypes) longer than carapace, 1.3 (holotype) or 1.5 × (paratypes) longer than P2 propodus; P3 merus 1.2 × (holotype) or 1.3 × (paratypes) longer than P3 propodus, P4 merus 0.9 × (holotype) or 1.3 × (paratypes) length of P4 propodus. Carpi unarmed, successively shorter posteriorly; carpus-propodus length ratio, 0.8 (holotype) or 1.0 (paratypes) on P2, 0.7 (holotype) or 0.8 (paratypes) on P3, 0.6 (holotype) or 0.8 (paratypes) on P4. Propodi subequal (holotype) or successively shorter posteriorly (paratypes); flexor margin straight, ending in pair of terminal spines preceded by 8 (holotype) or 11 (paratypes) spines on P2, 7 or 8 spines on P3, 7 spines on P4, proximal-most distinctly remote from proximal second. Dactyli subequal, 0.4 × as long as propodi, much shorter than carpi (dactylus-carpus length ratio, 0.5 on P2, 0.6 on P3 and P4); flexor margin gently curving, ending in slender spine preceded by row of 9 or 10 sharp triangular, somewhat obliquely directed, proximally diminishing spines.

Color. Holotype, ovigerous female (MNHN-IU-2010-5436): Generally translucent light purplish blue, with scattered brown spots, setae whitish. One of the Japanese specimens is illustrated by Kawamoto & Okuno (2003: 98).

REMARKS — The morphological differences between the holotype from Vanuatu and the paratypes from the Ryukyu Islands, Japan (see above under the description) leave some doubt about their identity, given that these specimens are from disjunct localities. On the other hand, the elongate eyestalks, tufts of long and whitish setae on the body and appendages, and the general colorations are consistent. These differences are here considered to be size-related, the Japanese specimens being much larger than the Vanuatu specimen. It is worth noting that this species appears to be a shallow water inhabitant.

The carapace spination is very similar to that of U. angustus n. sp. (see above) but not exactly the same. The metagastric spines are two in number, placed side by side in U. setifer , instead of a single as in U. angustus . Uroptychus setifer is readily distinguished from U. angustus by the following differences: the rostrum is laterally unarmed instead of bearing a subterminal spine on each side; the abdominal somite 1 is convex from anterior to posterior instead of bearing a distinct transverse ridge; the eyes are elongate and distally narrowed instead of uniformly broad proximally and distally; the antennal article 2 is unarmed instead of bearing a small but distinct distolateral spine; P2-4 are much more slender and unarmed instead of bearing spines on the dorsal or extensor margins of meri, carpi and propodi; the P2-4 dactyli are much shorter than instead of at most subequal to the carpi; and the pterygostomian flap is anteriorly roundish with a very tiny spine instead of being produced to a strong spine. In addition, U. setifer is distinctive in having longer setae in tufts on pereopods. It is worth noting that the breadth of the antennal article 5 is greater than the height of the antennular ultimate article in U. setifer and U. angustus , the unusual character also shared by U. buantennatus n. sp.

The spinose carapace and P1, the unarmed abdomen, and the spineless P2-4 meri and carpi link the species to U. fusimanus Alcock & Anderson, 1899 . This congener is known only by the type material with the brief description. However, U. setifer is readily differentiated from that species by the less spinose carapace and P1 and by having the antennal scale barely reaching instead of fully reaching the tip of the peduncle.

According to Kawamoto & Okuno (2003, 2006), the species is rare in the Ryukyu Islands and found associated with antipatharians (black corals) growing on overhanging rocks of drop-offs in the open sea with good tidal current.

Figures

FIGURE 237 Uroptychus setifer n.sp.,holotype,ovigerous female 2.2 mm (MNHN-IU-2010-5436).A, carapace and anterior part of abdomen,proximal part of left P1 included, dorsal. B, same, lateral.C, sternal plastron, with excavated sternum and basal parts of Mxp1. D, telson. E, right antenna, ventral.F, right Mxp3,lateral.G, same, ventral.Scale bars:A-D, 1 mm; E-G, 0.5 mm.

FIGURE 238 Uroptychus setifer n. sp.,holotype,ovigerous female 2.2 mm (MNHN-IU-2010-5436).A, left P1, dorsal.B, left P2,lateral.C, same, distal part,setae omitted,lateral. D, left P3,lateral. E, left P4,lateral.Scale bars:1 mm.

FIGURE 306 A,Uroptychuspsilus n.sp.,paratype,male 9.1 mm,MNHN-IU-2014-16888,NorfolkRidge.B,U.senarius n.sp.,paratype,ovigerous female4.9 mm,MNHN-IU-2014-16946, Vanuatu. C, U. setifer n. sp., holotype, ovigerous female 2.2 mm, MNHN-IU-2010-5436,Vanuatu. D, U. soyomaruae Baba, 1981, ovigerous female 14.0 mm, MNHN-IU-2014-16954,Norfolk Ridge. E, U.spinirostris (Ahyong & Poore,2004),3.6 mm, MNHN-IU-2014-16959,Vanuatu.F, U.stenorhynchus n. sp., paratype, male 6.0 mm, MNHN-IU-2014-16973,Vanuatu.G, U.trispinatus n. sp.,paratypes,male 5.2 mm (left), ovigerous female 4.8 mm (right), MNHN-IU-2014-16997, Chesterfield Islands.H, U. yokoyai Ahyong & Poore, 2004, female 3.2 mm, MNHN-IU-2014-17032,Vanuatu.I, Heteroptychus anouchkae n. sp., paratype, male 4.7 mm, MNHN-IU-2014-17101,Norfolk Ridge.