Uroptychus compressus, Baba & Wicksten, 2019

Baba, Keiji & Wicksten, Mary K., 2019, Chirostyloidean squat lobsters (Crustacea: Decapoda: Anomura) from the Galapagos Islands, Zootaxa 4564 (2), pp. 391-421 : 408-411

Uroptychus compressus n. sp.

( Figs. 12 , 13 )

Type material. CDF NA064-010-01-02-A, holotype, female (CL 3.1 mm), ROV Dive H1435, East Wolf Seamount, 1°12.986'N, 91°05.59539'W, 1068.7 m, with sponge, 27 June 2015.

Description. Carapace: As long as broad; greatest breadth measured at posterior third, 1.5 × distance between anterolateral spines. Dorsal surface smooth, glabrous and unarmed, moderately convex from anterior to posterior and from side to side, without depression between gastric and cardiac regions. Lateral margins convexly divergent posteriorly; ridged along posterior third; anterolateral spine well developed, horizontally directed slightly mesially, distinctly overreaching small lateral orbital spine. Rostrum triangular, laterally concave above eyes, with interior angle of 28°, horizontal and directed straight forward; length 0.4 × postorbital carapace length, breadth 0.6 × carapace breadth measured at posterior carapace margin; surface concave. Pterygostomian flap anteriorly roundish, with obsolescent spine, surface smooth.

Thoracic sternum: Excavated sternum anteriorly ending in sharp spine, surface ridged in midline. Sternal plastron as long as broad, lateral extremities weakly divergent posteriorly between sternites 4 and 6, subparallel between sternites 6 and 7. Sternite 3 moderately depressed, with broadly V-shaped anterior margin bearing 2 submedian spines separated by U-shaped sinus, anterolateral angle blunt, lateral end with tiny spine. Sternite 4 anterolateral margin convex, anteriorly ending in anterolaterally directed spine of moderate size, followed by 2 or 3 posteriorly diminishing spines, length 1.7 × that of posterolateral margin. Anterolateral margins of sternite 5 subparallel but anteriorly convex, 1.2 × longer than posterolateral margin of sternite 4.

Abdomen: Tergites smooth, glabrous. Somite 1 tergite dorsally convex from anterior to posterior, without transverse ridge. Somite 2 tergite 2.8 × broader than long; pleuron posterolaterally blunt, lateral margins somewhat concavely divergent posteriorly. Pleura of somites 3 and 4 laterally blunt. Telson 0.6 × as long as broad; posterior plate feebly convex on posterior margin, length 1.7 × that of, breadth 0.7 × that of anterior plate.

Eye: Short relative to breadth (1.1 × longer than broad), slightly convex on lateral margin, ending in distal quarter of rostrum. Cornea not dilated, slightly (1.1 or 1.2 ×) longer than remaining eyestalk.

Antennule and antenna: Ultimate article of antennular peduncle 2.3 × longer than high. Antennal peduncle slightly overreaching cornea. Article 2 with small but distinct distolateral spine. Antennal scale as broad as article 5, terminating in distal fifth point of article 5. Distal 2 articles unarmed; article 5 1.6 × longer than article 4, breadth 0.5 × height of ultimate antennular article. Flagellum of 10 or 11 segments overreaching rostrum by three-quarters of its length, overreaching P1 merus by distal 2 segments.

Mxp: Mxps 1 with bases distinctly separated from each other. Mxp 3 sparsely setose except for brushes on distal three articles; basis with 3 denticles on mesial ridge; ischium with 18 denticles on crista dentata, flexor margin not rounded distally; merus unarmed, 2.3 × longer than ischium, relatively thick mesio-laterally, flexor margin roundly ridged; carpus with low prominence on proximal extensor margin.

P1: Relatively massive, moderately setose on fingers, sparsely so on carpus and palm, glabrous elsewhere; length 3.6 × carapace length. Ischium with short dorsal spine, ventrally unarmed. Merus 0.9 × carapace length, distally subcylindrical, proximally compressed mesio-laterally (strongly narrowed in dorsal view). Carpus as long as merus, depressed (height 0.6 × breadth at midlength). Palm 2.3 × longer than broad, convex dorsally and ventrally, height 0.7 × breadth at midlength, length subequal to that of carpus. Fingers curving ventrally, distally incurved and crossing when closed, opposable margins dentate and straight, not gaping; movable finger 0.6 × length of palm.

P2–3: P4 missing. Meri mesio-laterally compressed and unarmed; P3 merus 0.8 × length of, and slightly narrower than, P2 merus; length-breadth ratio, 4.5 or 4.6 on P2, 4.1 on P3; dorsal margins sharply crested; P2 merus as long as P1 merus, 0.9 × length of carapace, very slightly longer than P2 propodus; P3 merus 0.9 × length of P3 propodus. Carpi 1.2 × longer on P2 than on P3; carpus-propodus length ratio, 0.6 on P2, 0.5 on P3. Propodi slightly longer on P2 than on P3; flexor margin slightly convex medially, with pair of movable spines preceded by 6 (left) or 5 (right) unpaired spines, distalmost of unpaired spines much remote from distal pair and adjacent to distal second on P2, remotely equidistant between distal pair and distal second spine on P3. Dactyli curving at proximal quarter, length 0.4 × that of propodus on P2, 0.5 × on P3; dactylus-carpus length ratio, 0.7 on P2, 0.9 on P3; flexor margin with 8 obliquely directed, relatively widely spaced, proximally diminishing spines, proximal spines more oblique, ultimate spine subequal to penultimate and antepenultimate.

Color: Pale yellowish orange, anterior part of carapace around rostrum reddish. A photo available in hand is too small so as to be included here.

Etymology. From the Latin compressus (= compressed) in reference to the mesiolaterally compressed P1 merus.

Remarks. This species resembles U. occidentalis Faxon, 1893 in having the smooth, unarmed carapace lateral margin except for the anterolateral spine, which readily separates these two species from the other four eastern Pacific species. Uroptychus compressus n. sp. is distinguished from U. occidentalis by the epigastric region being smooth instead of bearing a pair of short rows of granulations or denticles, the pterygostomian flap being more roundish anteriorly, the P1 merus being more strongly compressed proximally, and the P2–4 propodi having different spination: the distalmost of the unpaired flexor marginal spines is considerably distant from, instead of close to, the terminal pair of spines.

The present specimen was collected together with a sponge, but these were probably not associated. Symbiotic relationships between sponges and Uroptychus species have not been recorded to date ( Baeza 2011).

Distribution. East Wolf Seamount, Galapagos Rift zone, at 1068.7 m depth.

Figures

FIGURE 12. Uroptychus compressus n. sp., holotype, female (CL 3.1 mm), CDF NA064-010-01-02-A. A, carapace and anterior part of abdomen, dorsal. B, same, lateral. C, sternal plastron, with excavated sternum and basal parts of Mxp1. D, telson. E, left antenna, ventral. F, right Mxp3, ventral. G, same, lateral. Scales = 1 mm.

FIGURE 13. Uroptychus compressus n. sp., holotype, female (CL 3.1 mm), CDF NA064-010-01-02-A. A, right P1, dorsal. B, same, proximal part, lateral. C, same, distal articles omitted, ventral. D, same, distal part, mesial. E, same, fingers, setae omitted, ventral. F, left P2, lateral. G, same, distal part, setae omitted. H, right P2, lateral. I, same, distal part. J, left P3, lateral. K, same, distal part. Scales = 1 mm.