Uroptychus pedanomastigus, 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 : 388-392

Uroptychus pedanomastigus n. sp.

Figures 192 , 193

TYPE MATERIAL — Holotype: New Caledonia, Norfolk Ridge. BIOCAL Stn CP 30, 23°09’S, 166°41’E, 1140 m, 29.VIII.1985, 1 ov. ♀ 3.5 mm ( MNHNIU-2012-679 ).

ETYMOLOGY„ From the Greek pedanos (short) plus mastigos (whip), alluding to a short antennal flagellum possessed by the new species.

DESCRIPTION„ Small species. Carapace: Much broader than long (0.7 × as long as broad), broadest on posterior third; greatest breadth 2.1 × distance between anterolateral spines. Dorsal surface strongly convex from anterior to posterior, moderately from side to side, without depression, sparsely covered with short fine setae. Lateral margins convexly divergent posteriorly, granulate, and weakly ridged along posterior half; anterolateral spine small, slightly larger than lateral orbital spine, directed anteromesially. Rostrum deflected ventrally in proximal two-thirds, horizontal in distal third, narrow triangular, with interior angle 20°; dorsal surface feebly concave; lateral margin with 2 spines distally, proximal one obsolescent; length two-thirds that of remaining carapace, breadth about half carapace breadth at posterior carapace margin. Lateral orbital angle with small, distinct spine separated from anterolateral spine by basal breadth of latter spine, and located somewhat anterior to level of that spine. Pterygostomian flap smooth on surface, anterior margin angular, produced to distinct spine; anterior half much higher (about 2 x) than posterior half.

Sternum: Excavated sternum with triangular anterior margin; surface smooth, with weak low ridge in midline. Sternal plastron 0.7 × as long as broad, lateral extremities convexly divergent posteriorly; broadest on sternite 6. Sternite 3 shallowly depressed; anterior margin in broad V-shape without median notch and submedian spines. Sternite 4 with anterolateral margin convex and denticulate, 2 × longer than posterolateral margin. Anterolateral margin of sternite 5 anteriorly convex, 1.3 × longer than posterolateral margin of sternite 4.

Abdomen: Somite 1 weakly convex from anterior to posterior, without transverse ridge. Somite 2 tergite 2.7 × broader than long; pleural lateral margin concave, slightly divergent posteriorly, posterolateral end blunt. Pleuron of somite 3 with blunt posterolateral margin. Telson 0.4 × as long as broad; posterior plate as long as anterior plate, posterior margin medially deeply concave.

Eye: 1.4 × longer than broad, distally narrowed. Cornea not inflated, half as long as remaining eyestalk.

Antennule and antenna: Ultimate article of antennule 3.2 × longer than high. Antennal peduncle overreaching cornea, barely reaching midlength of rostrum. Article 2 with small distolateral spine. Antennal scale tapering distally, 1.9 × broader than article 5, overreaching distal end of article 5, slightly overreaching eye but not reaching apex of rostrum. Articles 4 and 5 each with small distomesial spine; article 5 1.2 × longer than article 4, breadth about half height of antennular ultimate article. Flagellum of 6 or 7 segments barely reaching rostral tip, far falling short of distal margin of P1 merus.

Mxp: Mxp1 with bases broadly separated. Mxp3 with fine plumose setae other than brushes on distal articles. Basis having mesial ridge proximally lobe-like and nearly smooth. Ischium with flexor margin not rounded distally; crista dentata with more than 35 denticles distally diminishing. Merus 2.4 × longer than ischium, with obsolescent distolateral spine; flexor margin roundly ridged, with a few tubercles on distal half. Carpus unarmed.

P1: 4.3 × longer than carapace, sparklingly with short fine soft setae along mesial and lateral margins. Ischium with small dorsal spine, ventromesial margin with row of very small spines, with or without obsolescent subterminal spine. Merus with small distomesial and distolateral spines on ventral surface and tubercle-like small spines on distodorsal margin, unarmed elsewhere, length subequal to that of carapace. Carpus subcylindrical, 1.2 × longer than merus, distodorsal margin with row of small, denticle-like spines. Palm 4.0 × longer than broad, 1.2 × longer than carpus. Fingers moderately depressed and relatively broad, distally incurved, crossing when closed, feebly gaping, denticulate on opposable margins; fixed finger with low eminence at midlength of opposable margin; movable finger 0.4 × as long as palm, opposable margin with marginally denticulate process proximal to midlength, fitting to longitudinal groove on opposite face of fixed finger when closed.

P2-4: Relatively thick mesio-laterally, with fine soft setae. Meri successively shorter posteriorly (P3 merus 0.8 × length of P2 merus, P4 merus 0.8 × length of P3 merus); breadths slightly greater on P3 and P4 than on P2; length-breadth ratio, 4.0 on P2, 3.7 on P3, 3.2 on P4; dorsal margins rounded, not carinated, unarmed; P2 merus 0.7 × as long as carapace, subequal to length of P2 propodus; P3 merus 0.9 × length of P3 propodus; P4 merus 0.7 × length of P4 propodus. Carpi subequal on P2 and P3, slightly shorter on P4; carpus-propodus length ratio, 0.5 on P2 and P3, 0.3 on P4; carpus-dactylus length ratio, 1.2 or 1.3 on P2, 1.0 on P3, 0.6 on P4; extensor margin with obsolescent proximal process. Propodi subequal on P2 and P3 and longer on P4; flexor margins moderately convex on distal portion on P2, less so on P3, feebly so on P4; ending in pair of terminal spines preceded by 6 (right) or 8 (left) spines on P2, 8 on P3, 5 on P4, all along entire length, those on proximal half much smaller and broadly spaced from one another. Dactyli 0.4 × as long as propodi on P2, 0.5 × on P3 and P4; dactylus-carpus length ratio, 0.8 on P2, 1.0 on P3, 1.6 on P4; flexor margins somewhat curving, with 7, 7, 8 well-developed, triangular spines on P2, P3, P4 respectively, ultimate strongest, remaining spines proximally diminishing and perpendicular to margin.

Eggs. Number of eggs carried, 3; size, 1.03 × 1.00 mm - 1.13 × 0.96 mm.

REMARKS — This species resembles U. edisonicus Baba & Williams, 1998 from the hydrothermal vent site at Edison Seamount, Bismarck Archipelago, U. latior n. sp. and U. norfolkanus n. sp. (for their similarity, see above under the account of U. latior ). Uroptychus pedanomastigus is distinguished from U. edisonicus ( Figure 121 ) by the anterolateral spine that is directed anteromesially instead of straight forward; the excavated sternum has a triangular instead of convex anterior margin; the P2-4 propodi bear flexor marginal spines placed along the entire margin (although proximal spines are widely spaced) instead of restricted to the distal portion. Uroptychus pedanomastigus and U. latior n. sp. share the anteromesially directed anterolateral spine of the carapace, the P2-4 carpi bearing a small proximal process on the extensor margin, and the Mxp3 crista dentata bearing a row of regularly arranged small denticles. However, U. pedanomastigus is distinctive in the anterior margin of the excavated sternum that is triangular instead of gently convex; the antennal scale slightly overreaching instead of extending far beyond the eye; the antennal flagellum barely reaching instead of extending far beyond the apex of the rostrum; the P2-4 propodi bearing additional loosely arranged spines proximal to the closely arranged distal group of flexor marginal spines; and the P2-4 dactyli bearing flexor marginal spines perpendicularly instead of obliquely directed.

Uroptychus pedanomastigus is distinguished from U. norfolkanus by the excavated sternum that is triangular instead of convex on the anterior margin; the anterolateral spine of the carapace is directed anteromesially rather than straight forward and closer to instead of more distant from the lateral orbital spine (this is clearly recognizable when viewed from dorsal side); the flexor marginal spines of the P2-4 dactyli are perpendicularly instead of obliquely directed; and the flexor margin of the P3 propodus (P2 and P4 are missing in U. norfolkanus ) bears three instead of one spine remotely proximal to the distal group of closely arranged spines. In addition, the P3 propodus is more strongly inflated on the distal flexor margin in U. norfolkanus . Generally this inflation becomes weaker in smaller specimens ( Ahyong et al. 2015, for U. insignis ( Henderson, 1885)) , but the ovigerous female of U. norfolkanus is smaller than the ovigerous female holotype of U. pedanomastigus .

Figures

FIGURE 121 Uroptychus edisonicus Baba& Williams,1998,holotype,ovigerous female 4.6 mm,USNM 251479.A, anterior part of carapace,dorsal.B, anterior part of sternal plastron,excavated sternum and basal parts of Mxp1 included.C, left Mxp3,crista dentata,ventral.D, right P2,setae omitted,lateral.E, same, distal part, setae omitted.F, right P3,lateral.G, same, distal part, lateral.H, right P4,lateral.Scale bars:A,B, D-H,1 mm; C,0.5 mm.

FIGURE 192 Uroptychus pedanomastigus n. sp.,holotype,ovigerous female 3.5 mm (MNHN-IU-2012-679).A, carapace and anterior part of abdomen,proximal part of right P1 included, setae on carapace omitted, dorsal. B, same,setae omitted, lateral.C, sternal plastron,with excavated sternum and basal parts of Mxp1. D, telson. E, left antenna,ventral.F, left Mxp3,ventral.H, same,lateral.Scale bars:1 mm.

FIGURE 193 Uroptychus pedanomastigus n. sp., holotype, ovigerous female 3.5 mm (MNHN-IU-2012-679). A, right P1, proximal part, setae omitted, ventral. B, same,distal three articles,dorsal.C, same,fingers,setae omitted,ventral.D, right P2, lateral.E, left P3,setae omitted, lateral.F, same,distal part, lateral.G, right P4, lateral.H, same,distal part,lateral.Scale bars:1 mm.