Uroptychus tridentatus ( Henderson, 1885 )

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 : 527-531

Uroptychus tridentatus ( Henderson, 1885)

Figures 266 , 267

Diptychus tridentatus Henderson, 1885: 421 .

Uroptychus tridentatus — Henderson 1888: 181, pl. 6, figs 1, 1a. — Van Dam 1933: 30, figs 45, 46; 1937: 99. — Baba 2005: 61 (part, type material only; other specimens = U. annae n. sp.), figs 20.

? Uroptychus tridentatus — Baba 1990: 948.

Not Uroptychus tridentatus — Baba 1973: 117 (different species, see below).

TYPE MATERIAL — Holotype: Indonesia, East Indian Archipelago [Ambon], 15 fms (27 m), ov. female ( BMNH 1888 :33). [not examined].

MATERIAL EXAMINED — Philippines. MUSORSTOM 3 Stn CP134, 12°01’N, 121°57’E, 92-95 m, 5.VI.1985 ,1 ov. ♀ 3.4 mm (MNHN-IU-2014-16995).

DISTRIBUTION„ Banda Sea ( Ambon and Kai Islands), N of the Sulu Islands, Solor Strait [between Solor and Alor Archipelagos, in 27-304 m; now Philippines (off NW of Panay), 92- 95 m.

DESCRIPTION„ Small species. Carapace: Slightly broader than long; greatest breadth 2.2 × distance between anterolateral spines. Dorsal surface with sparse, relatively long setae, unarmed, slightly convex from anterior to posterior. Lateral margins posteriorly divergent to point one-quarter from posterior end, then convergent, with 7 spines: first anterolateral, overreaching small lateral orbital spine; second and third much smaller, situated at same level as first spine in lateral view and ventral to level of posterior spines; fourth to seventh larger, placed on branchial region, seventh situated at point one-quarter from posterior end. Rostrum triangular, with interior angle of about 30°, bearing subterminal small spine on each side; dorsal surface concave; length slightly less than half that of remaining carapace, breadth about half carapace breadth at posterior carapace margin. Lateral orbital spine small, located directly mesial to anterolateral spine. Pterygostomian flap anteriorly sharp angular, produced to sharp spine, surface with small spines on anterior half, anterior half about as high as posterior half.

Sternum: Excavated sternum with convex anterior margin, ventral surface roundly ridged in midline. Sternal plastron shorter than broad (length 0.8 × breadth), lateral extremities slightly divergent posteriorly. Sternite 3 depressed well, anterior margin shallowly concave, with narrowly U-shaped median notch with small incurved flanking spine; posterolateral margin much more than half (0.8 x) length of anterolateral margin. Anterolateral margins of sternite 5 subparallel, about as long as posterolateral margin of sternite 4.

Abdomen: Somite 1 tergite well convex from anterior to posterior. Somite 2 tergite 2.3 × broader than long; pleuron with lateral margin moderately concave and moderately divergent posteriorly leading to blunt terminus. Pleuron of somite 3 posterolaterally bunt. Telson 0.4 × as long as broad; posterior plate 1.2 × longer than anterior plate, posterior margin feebly concave.

Eyes: 1.7 × longer than broad, distally slightly narrowed, overreaching distal third of rostrum; cornea more than half length of remaining eyestalk.

Antennule and antenna: Ultimate article of antennular peduncle 3.6 × longer than high. Antennal peduncle reaching apex of cornea. Article 2 with acute lateral spine. Antennal scale reaching second segment of flagellum. Distal 2 articles each with strong distomesial spine; article 5 1.7 × longer than article 4, breadth 0.8 × height of ultimate article of antennule. Flagellum of 10 or 11 segments not reaching distal end of P1 merus.

Mxps: Mxp1 with bases broadly separated. Mxp3 basis without denticles on mesial ridge. Ischium with small spine lateral to rounded distal end of flexor margin, crista dentata with about 17 denticles. Merus 2.0 × longer than ischium, flattish, with distolateral spine and 2 small spines around distal third of flexor margin. Carpus with distolateral spine and 3 small spines long extensor margin.

P1: Relatively massive, 4.5 × longer than carapace, with relatively long fine setae. Ischium with strong dorsal spine and well-developed subterminal spine on ventromesial margin. Merus with a few small ventral spines proximally, short ventromesial and ventrolateral spines distally, length 1.2 × that of carapace. Carpus 0.9 × length of merus. Palm 3.2 × longer than broad, length 1.2 × longer than carpus. Fingers distally slightly incurved, crossing when closed, not gaping and straightly fitting along opposable margins; movable finger 0.5 × length of palm, opposable margin with low blunt proximal process fitting to longitudinal groove on opposite face of fixed finger when closed.

P2-4: P4 missing. Meri compressed mesio-laterally and relatively broad, mesial face flattish, P2 merus subequally long and broad as P3 merus, with length-breadth ratio 3.4; dorsal margin with 4 small spines on P2, 2 proximal spines on P3, ventrolateral margin with small distal spine; P2 merus 0.8 × length of carapace, subequal to P2 propodus; P3 merus 0.9 × as long as P3 propodus. Carpi slightly shorter on P3 than on P2, unarmed, length 0.4 × that of propodus. Propodi slightly longer on P3 than on P2; flexor margin slightly concave, with pair of terminal spines preceded by 5 spines on P2, 6 spines on P3. Dactyli slightly longer on P3 than on P2, dactylus-carpus length ratio, 1.0 on P2, 1.3 on P3; flexor margin nearly straight, bearing slender terminal (ultimate) spine preceded by 8 triangular, somewhat obliquely directed, loosely arranged, proximally diminishing spines, penultimate subequal to antepenultimate.

Eggs. Number of eggs carried, 6; size, 0.75 × 0.90 mm - 0.76 × 0.93 mm.

REMARKS — The type material is now in poor condition, with all the pereopods missing. In my earlier paper ( Baba, 2005), the specimens from New Caledonia (MNHN-IU-2014-17292, MNHN-IU-2014-17298) were thought to be identical with U. tridentatus . However, the present sole specimen has the carapace much more like that of the type, especially with the last lateral spine being located at a point in the posterior quarter rather than posterior third. Its occurrence is near to the type locality of U. tridentatus rather than being far south in New Caledonia and vicinity. In addition, their bathymetric range is shallow, unlike that of the specimens of Baba (2005), which were from below 290 m. The specimens of Baba (2005) are now described as U. annae n. sp. (see above). The present specimen has more numerous spines on the P2-4 propodi and dactyli (see above under U. annae ).

The identification of the SIBOGA material from the Sulu Sea and Kai Islands ( Van Dam, 1933) appear to be correct. The material reported by Van Dam (1937) from Solor Strait [between Solor and Alor Archipelago] may also be referable to this species, judging from her note that the specimen agrees well with her description of SIBOGA material.

The material reported from Japan ( Baba, 1973) is also different from the present material in having only 3 spines on the branchial lateral margin with the last one located slightly posterior to the midlength of the carapace lateral margin, in having the P2-4 propodi with a pair of terminal spines preceded by 2, 0, 0 spine on P2, P3, P4 respectively, the features suggesting that it is close to U. zezuensis . However, U. zezuensis has the last branchial marginal spine distinctly more anterior in position. The Japanese material is now removed from the synonymy, requiring further study. The specimens from Madagascar ( Baba, 1990) are very similar to the present material but differ in having more slender P2-4, especially the dactyli, and in having a few additional spines proximal to the distal spine on the meral ventrolateral margin. This is removed from the synonymy, pending extensive studies.

Uroptychus inclinis Baba, 2005 from the Kai Islands is now synonymized with U. tridentatus . The lateral carapace margins of U. inclinis seem to be more convex than those of both the holotype and the present material of U. tridentatus , but no additional difference worthy of note is found.

Figures

FIGURE 266 Uroptychus tridentatus (Henderson, 1885), ovigerous female 3.4 mm (MNHN-IU-2014-16995). A, carapace and anterior part of abdomen,dorsal.B, same,lateral.C, sternal plastron,with excavated sternumand basal parts of Mxp1.D,telson.E,right antenna, ventral.F, left Mxp3, ventral.G, same,lateral.Scale bars:1 mm.

FIGURE 267 Uroptychus tridentatus (Henderson,1885),ovigerous female 3.4 mm (MNHN-IU-2014-16995).A, left P1,dorsal.B, same,proximal part, setae omitted, ventral.C, same, distal part, ventral. D, left P2, lateral. E, same, distal part, setae omitted,lateral.F, left P3, lateral.G, same, distal part, lateral. Scale bars: 1 mm.