Uroptychus diaphorus, 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 : 175-178

Uroptychus diaphorus n. sp.

Figures 74 , 75

TYPE MATERIAL — Holotype: Tonga. BORDAU 2 Stn DW 1595, 19°03’S, 174°19’W, 523-806 m, 14.VI.2000, ov. ♀ 2.8 mm ( MNHN-IU-2014-16389 ).

ETYMOLOGY„ From the Greek diaphoros (different), alluding to an unusually slender P2 especially distal two articles.

DISTRIBUTION„ Tonga; 523- 806 m.

DESCRIPTION„ Small species. Carapace: 1.2 × as broad as long (0.8 × as long as broad); greatest breadth measured around posterior end, 1.5 × distance between anterolateral spines. Dorsal surface slightly convex from anterior to posterior, with very feeble depression between gastric and cardiac regions; smooth, with very sparse setae. Lateral margins slightly convex and divergent posteriorly, bearing 6 spines: first anterolateral, small, not reaching tip of lateral orbital spine; second larger than first, subequal to third, located at anterior end of anterior branchial margin, equidistant between first and third; third to sixth on posterior branchial region; last one small (obsolescent on right side), followed by ridge. Rostrum sharp triangular with interior angle of 26°, straight horizontal in profile; length 0.6 × postorbital carapace length, breadth less than half carapace breadth measured at posterior carapace margin; dorsal surface moderately concave, lateral margin entire. Lateral orbital spine larger than and relatively close to anterolateral spine. Pterygostomian flap anteriorly somewhat roundish, produced to small spine, surface smooth.

Sternum: Excavated sternum strongly depressed, surface with weak ridge in midline, anterior margin bluntly subtriangular between bases of Mxp1. Sternal plastron slightly broader than long, lateral extremities somewhat divergent posteriorly. Sternite 3 moderately depressed, anterior margin moderately concave, with narrow V-shaped median notch flanked by very small spine, anterolaterally angular. Sternite 4 having anterolateral margin nearly straight and entire, anteriorly ending in triangular process, posterolateral margin half as long as anterolateral margin. Anterolateral margins of sternite 5 subparallel, anteriorly rounded, length 1.3 × that of posterolateral margin of sternite 4.

Abdomen: Smooth, very sparsely setose. Somite 1 moderately convex from anterior to posterior, without ridge. Somite 2 tergite 2.2 × broader than long; pleural lateral margin weakly concave and weakly divergent posteriorly, posterolaterally rounded. Pleuron of somite 3 posterolaterally bluntly angular. Telson slightly less than half as long as broad; posterior plate with rounded posterior margin, length 1.5 × that of anterior plate.

Eye: Terminating in anterior third length of rostrum, lateral and mesial margin somewhat convex. Cornea not dilated, slightly shorter than remaining eyestalk.

Antennule and antenna: Antennular ultimate article 2.8 × longer than high. Antennal peduncle reaching distal end of cornea. Article 2 without spine on lateral margin. Antennal scale 1.4 × broader than article 4, reaching first segment of flagellum. Article 4 with distinct distomesial spine. Article 5 as long as article 4, bearing small distomesial spine; breadth slightly more than half height of antennular ultimate article. Flagellum consisting of 14 segments, falling short of distal end of P1 merus.

Mxp: Mxp1 with bases broadly separated. Mxp3 having basis smooth on mesial ridge. Ischium with distally rounded flexor margin accompanying a few setae lateral to it; crista dentata without denticles. Merus 2 × longer than ischium, well compressed, mesially flattish, distolateral spine distinct; flexor margin with a few small spines distal to angular point one-third from distal end. Carpus unarmed.

P1: Left P1 missing. Right P1 5.5 × longer than carapace, slender, smooth and polished, sparsely setose but fingers more setose. Ischium with strong, sharp dorsal spine, ventrally unarmed but 2 tubercular processes on proximal mesial margin. Merus 1.3 × longer than carapace, mesially with strong spine at midlength and 2 tiny spinules, ventrally bearing distomesial and distolateral spines, both small but distomesial larger. Carpus 1.2 × longer than merus, ventrally bearing distomesial and distolateral spines, dorsally bearing 2 tubercular processes directly distal to juncture with merus. Palm 3.7 × longer than broad, slightly longer than carpus, somewhat depressed. Fingers somewhat incurved distally, crossing when closed; movable finger one-third length of palm; opposable margin of movable finger with low, subtriangular (in dorsal view) process proximal to similarly low process placed at midlength of fixed finger.

P2-4: P3 missing on both sides. P2 and P4 rather flattish, setose like P1. P2 much more slender than P4, especially distal 2 articles; merus 5.9 × longer than broad, slightly longer than carapace, unarmed; carpus 0.4 × length of propodus, slightly shorter than dactylus; propodus distally narrowed, 6.2 × longer than broad at proximal portion of greatest breadth; flexor margin ending in pair of spines preceded by 1 spine; length about twice that of dactylus; dactylus moderately curved, flexor margin with 8 spines, ultimate slender, penultimate pronouncedly broad, remaining spines small (discernible under high magnification), oriented parallel to margin and loosely arranged. P4 merus 3.5 × longer than broad, 0.7 × as long as and 1.2 × broader than P2 merus, 0.9 × length of P4 propodus; carpus as long as that of P2, slightly less than half length of dactylus; propodus and dactylus longer and broader than on P2; propodus 2.8 × length of carpus, flexor margin ending in pair of spines preceded by 1 spine; dactylus 2 × length of carpus, 0.7 × length of propodus, well compressed, flexor margin somewhat curved, with strongly inclined spines distinctly larger than those on P2, penultimate 2 × broader than antepenultimate, proximally preceded by 11 blunt spines nearly contiguous to one another, ultimate more slender than antepenultimate.

Eggs. One egg carried on left half of abdomen, nearly ready to hatch, 1 exuvia on right side; size, 1.28 mm × 1.40 mm.

REMARKS — The new species is unique among the species of Uroptychus in having the propodus and dactylus of P2 much more slender and shorter than those of P4, with the dactylar spination different between P2 and P4 (P3 is missing in this species): the flexor marginal spines proximal to the pronounced penultimate spine are small, oriented parallel to the flexor margin and loosely arranged on P2, whereas these spines are larger, strongly inclined and nearly contiguous to one another on P4. The slender P2, which is different from P3 and P 4 in lacking flexor marginal spines on the dactylus, is one of the diagnostic characters of Uroptychodes Baba, 2004 . This species may likely be shifted to a different genus but is provisionally placed under Uroptychus awaiting molecular analysis.

The new species has the lateral carapace margin bearing a row of spines, the anterolateral spine of the carapace is smaller than the lateral orbital spine, the penultimate of the P2-4 dactylar spines is twice as broad as the antepenultimate, and the ultimate of the same is more slender than the penultimate, all characters shared by U. pronus Baba, 2005 . Uroptychus diaphorus differs from that species in having the antennal scale overreaching the antennal article 5 instead of barely reaching the tip of that article, in having both the P2 and P4 meri unarmed instead of bearing a row of spines along the dorsal margin, and more distinctly in having a different spination between P2 and P4 (see above).

Figures

FIGURE 74 Uroptychus diaphorus n.sp.,holotype,ovigerous female 2.8 mm (MNHN-IU-2014-16389).A,carapace and anterior part of abdomen, proximal part of right P1 included, dorsal. B, same, lateral. C, sternal plastron, with excavated sternum and basal parts of Mxp1. D, telson. E, left antenna,ventral.F, left Mxp3,ventral.G, same,lateral.H, right P1, dorsal.Scale bars:1 mm.

FIGURE 75 Uroptychus diaphorus n.sp.,holotype,ovigerous female 2.8 mm (MNHN-IU-2014-16389).A, left P2,lateral.B, same,distal part,setae omitted,lateral. C, left P4, lateral. D, same, distal part, setae omitted,lateral.Scale bars:1 mm.