Uroptychus strigosus, 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 : 506-509

Uroptychus strigosus n. sp.

Figures 254 , 255

TYPE MATERIAL — Holotype: Solomon Islands. SALOMON 1 Stn DW 1827, 9°59.1’S, 161°05.8’E, 804-936 m, 4.X.2001, ♂ 6.1 mm ( MNHN-IU-2014-16974 ).

ETYMOLOGY„ From the Latin strigosus (= full of striae), alluding to the transverse ridges on the carapace, which are interrupted and mostly scale-like, a rare character among Uroptychus species.

DISTRIBUTION„ Solomon Islands; 804- 936 m.

DESCRIPTION„ Carapace: 1.1 × broader than long (0.9 × as long as broad); greatest breadth 1.7 × distance between anterolateral spines. Dorsal surface with elevated, scale-like setiferous ridges; distinct groove between gastric and cardiac regions; gastric region somewhat convex. Lateral margins divergent to point two-thirds from anterior end, then convergent, bearing 7 spines: first anterolateral, stout, somewhat posterior to level of small lateral orbital spine, and distinctly overreaching that spine; second and third small, placed on hepatic region and ventral to level of remainder; fourth to seventh on branchial margin, fourth to sixth well developed, seventh small, situated at midlength of posterior branchial margin, followed by ridge leading to posterior end. Rostrum narrow triangular, with interior angle of 20°; dorsal surface flattish, with small scale-like ridges in 2 longitudinal rows; length 0.6 × that of remaining carapace, breadth much less than half carapace breadth at posterior carapace margin. Pterygostomian flap anteriorly angular, produced to small spine; surface with scattered short setiferous ridges.

Sternum: Excavated sternum with anterior margin subtriangular between bases of Mxp1; surface with rounded ridge in midline. Sternal plastron 1.2 × broader than long, posteriorly broadened. Sternite 3 strongly depressed, anterior margin in broad V-shape lacking median notch and submedian spines. Sternite 4 having anterolateral margin 1.4 × longer than posterolateral margin, anteriorly denticulate, with angular terminus. Sternite 5 with anterolateral margins subparallel, anteriorly rounded, about as long as posterolateral margin of sternite 4.

Abdomen: Somite 1 with well-elevated, setiferous transverse ridge. Somite 2 tergite 2.5 × broader than long; pleuron posterolaterally blunt, lateral margin slightly concave and slightly divergent posteriorly. Tergites of somites 2 and 3 covered with small scale-like striae, bearing interrupted, setiferous anterior transverse ridge. Pleuron of somite 3 laterally blunt angular. Telson half as long as broad; posterior plate slightly concave on posterior margin, length 1.2 × that of anterior plate.

Eye: Elongate, 2 × as long as broad, distally narrowed. Cornea about half as long as remaining eyestalk.

Antennule and antenna: Antennular ultimate article 3.2 × longer than high, reaching midlength of rostrum. Antennal peduncle extending far beyond cornea. Article 2 with small distolateral spine. Antennal scale overreaching proximal segment of flagellum, breadth 1.8 × that of article 5. Articles 4 and 5 each with distinct distomesial spine; article 5 2.0 × longer than article 4, breadth 0.7 × height of antennular ultimate article. Flagellum consisting of 17-18 segments, overreaching distal end of P1 merus.

Mxp: Mxp1 with bases moderately separated. Mxp3 with long setae on lateral surface. Obsolescent denticles on mesial ridge of basis. Ischium with numerous small denticles on crista dentata, proximal group of 4 denticles remotely separated from distal group; flexor margin distally rounded. Merus twice as long as ischium, with short distolateral spine; flexor margin sharply ridged, bearing a few papilla-like spines on distal third of length. Carpus with small distolateral spine.

P1: Right P1 missing. Left P1 subcylindrical, palm somewhat depressed; covered with short, scale-like setiferous ridges. Ischium dorsally with lobe-like process, ventromesially with very small subterminal spine and obsolescent proximal tubercles. Merus slightly shorter than carapace, dorsally with very small terminal spines near juncture with carpus, mesially with 1 distinct spine at midlength, ventrolaterally with small distal spine. Carpus with 2 tubercle-like processes directly distal to juncture with merus, and a number of spinules on dorsal terminal margin, length subequal to that of merus. Palm as long as carpus, 2.9 × longer than broad, unarmed. Fingers distally ending in short incurved spine; movable finger half as long as palm, opposable margin with very low proximal process, that of fixed finger nearly straight.

P2-4: Sparingly setose. Meri moderately compressed mesio-laterally, successively shorter posteriorly (P3 merus 0.9 × length of P2 merus, P4 merus 0.9 × length of P3 merus), equally broad on P2 and P3, slightly narrower on P4 (P4 merus 0.9 × breadth of P3 merus); length-breadth ratio, 4.0 on P2, 3.4 on P3, 3.2 on P4; dorsal margin irregular, with low eminences on P2 and P3, nearly smooth on P4; P2 merus 0.8 × length of carapace, as long as P2 propodus; P3 merus 0.9 × length of P3 propodus; P4 merus 0.7 × length of P4 propodus. Carpi successively slightly shorter posteriorly (P3 carpus 0.95 × length of P2 carpus, P4 carpus 0.92 × length of P3 carpus); shorter than dactyli (carpus-dactylus length ratio, 0.8 on P2, 0.7 on P7, 0.6 on P4), about 0.4 × as long as propodi; extensor margin with low eminence on proximal portion on P2, smooth on P3 and P4. Propodi subequal in length; flexor margin slightly concavely curving in lateral view, with pair of terminal spines only. Dactyli successively slightly longer posteriorly, proportionately broad; dactylus-carpus length ratio, 1.2 on P2, 1.5 on P3, 1.6 on P4; dactylus-propodus length ratio, 0.5 on P2, 0.6 on P3 and P4; flexor margin somewhat curving, sharply crested, with slender, obliquely directed, closely arranged spines, but penultimate spine pronouncedly broad, more than 3 × as broad as ultimate and antepenultimate.

REMARKS„ At first glance the species looks close to U. squamifer n. sp. in having the carapace with strong lateral spinens and covered with scale-like setiferous ridges and in having the abdominal somite 1 with a sharp transverse ridge, but it is closer to U. occultispinatus Baba, 1988 , sharing the P2-4 dactyli that bear a prominent penultimate spine proximally preceded by a row of closely arranged, obliquely directed, slender spines on the flexor margin. Uroptychus strigosus differs from U. occultispinatus in having the carapace dorsal surface with more distinct scale-like ridges and in having sternite 3 with the anterior margin more deeply emarginate. In addition, the rostrum is narrow triangular with the interior angle of 20° instead of more than 30° as interpreted from the figures in the previous species accounts of U. occultispinatus ( Balss 1913b: fig. 18; Baba 1988: fig. 14).

Uroptychus strigosus differs from U. squamifer in many aspects: the carapace dorsal surface is unarmed instead of bearing small spines on the anterior portion; the pterygostomian flap anteriorly ends in a small instead of strongly produced spine; sternite 3 represents a broad V-shaped anterior margin without submedian spines, instead of a shallowly concave anterior margin with two small submedian spines separated by a notch; the antennal scale overreaches the antennal peduncle instead of falling short of the distal end of the antennal article 5; the P2-4 meri, carpi and propodi are unarmed instead of bearing a row of spines on the dorsal or extensor margin; the P2-4 carpi are distinctly shorter instead of longer than the dactyli; and the flexor margin of the P2-4 dactyli bears a slender ultimate and a broad penultimate spine preceded by obliquely directed slender spines, instead of bearing all similar, sharp, slender spines subperpendicular to the margin.

Figures

FIGURE 254 Uroptychus strigosus n. sp., holotype, male 6.1 mm (MNHN-IU-2014-16974). A, carapace and anterior part of abdomen, proximal part of left P1 included, dorsal. B, same, lateral.C, sternal plastron, with excavated sternum, basal parts of Mxp1 included. D, telson. E, right antenna, ventral.F, right Mxp3,setae omitted, ventral.G, same, lateral.H, left Mxp3,crista dentata, ventral. Scale bars:1 mm.

FIGURE 255 Uroptychus strigosus n. sp., holotype, male 6.1 mm (MNHN-IU-2014-16974). A, Left P1, proximal part, ventral. B, same, dorsal.C, right P2, lateral. D, same,distal part,setae omitted,lateral. E, left P3,lateral.F, left P4,lateral.Scale bars:1 mm.