Uroptychus marissae, Baba, Keiji & Wicksten, Mary, 2015

Baba, Keiji & Wicksten, Mary, 2015, Uroptychus minutus Benedict, 1902 and a closely related new species (Crustacea: Anomura: Chirostylidae) from the western Atlantic Ocean, Zootaxa 3957 (2), pp. 215-225 : 220-224

Uroptychus marissae n. sp.

( Figs. 4–6 )

Type material. Holotype: male 1.6 mm, Rankin Bank, northern Gulf of Mexico, Remote operated vehicle, Station PSBF 2-3C, 27°55.167’N, 93°24.81’W, 89.3 m, on antipatharian Tanacetipathes sp., 19 Sept. 2012, Marissa Nuttall, coll. ( USNM 1251916). Paratype: 1 female 1.6 mm, collected with holotype ( USNM 1251917).

Etymology. Dedicated to Marissa Nuttall who collected the material.

Description. Small species. Carapace: 0.8–[0.9] × as long as broad ([1.1]–1.2 × broader than long); greatest breadth [1.4]–1.6 × distance between anterolateral spines. Dorsal surface unarmed and barely setose, moderately convex from side to side, slightly convex on gastric region, without depression. Lateral margins divergent posteriorly to point one-third from posterior end, with 6 spines; first anterolateral, moderately large, directed anteriorly, terminating in tip of lateral orbital spine, second to sixth smaller, nearly equidistant from one another, second somewhat posterior to midpoint between, and, somewhat dorsal to level of, first and third, last spine situated at proximal third of lateral margin. Rostrum directed slightly ventrally, broad triangular (1.2–[1.4] × broader than long), with interior angle of 36–[40]°, ending in sharp tip; dorsal surface concave; lateral margin smooth and slightly concave; length 0.4 × that of remaining carapace, breadth 0.7–[0.8] × length of posterior carapace margin. Lateral orbital spine subequal to, situated at same level as, anterolateral spine of carapace, directed anterolaterally. Pterygostomian flap anteriorly angular, produced to distinct spine, smooth on surface, posterior portion half as high as anterior portion, when measured between linea anomurica and ridge along ventral margin.

Sternum: Sternites 1–3 strongly produced anteriorly between bases of Mxp1, surface with sharp ridge in midline. Sternal plastron 0.8 × as long as broad, lateral extremities divergent posteriorly between sternites 4–7. Sternite 3 slightly depressed from level of sternite 4 in ventral view; anterior margin deeply concave in roughly semicircular shape, with very low, broadly triangular median process, lacking median spines and median sinus, anterolaterally sharp angular. Sternite 4 having anterolateral margin convex and anteriorly blunt angular; posterolateral margin half as long as anterolateral margin. Anterolateral margins of sternite 5 convex, 1.5 × longer than posterolateral margin of sternite 4.

Abdomen: With very sparse setae. Somite 1 weakly convex from anterior to posterior. Somite 2 tergite 2.5– [2.7] × broader than long; pleural lateral margins slightly concave, moderately divergent laterally (more distinctly in female), posterolaterally blunt. Pleura of somites 3–5 with rounded lateral margin. Telson half as long as broad; posterior plate 1.1–[1.6] × length of anterior plate, posterior margin very feebly concave, not emarginate.

Eye: [1.7]–1.9 × longer than broad, slightly narrowed distally, slightly overreaching rostral tip; lateral margins slightly diverging proximally. Cornea slightly less than half as long as remaining eyestalk, not dilated.

Antennule and antenna: Ultimate article of antennular peduncle 3.2 × longer than high. Antennal peduncles reaching rostral tip. Article 2 with distinct lateral spine. Antennal scale 1.5 × broader than article 4, ending in proximal third of length of article 5. Article 4 with small but distinct distomesial spine. Article 5 also with distinct distomesial spine, 1.5 × longer than article 4, breadth 0.5 × height of ultimate article of antennule. Flagellum of 6 segments slightly longer than articles 4 and 5 combined, exceeding beyond rostral tip by its full length.

Mxp: Mxp1 with bases broadly separated. Mxp3 basis without distinct denticle on mesial ridge. Ischium flexor margin not rounded distally, ending in small spine; crista dentata with about 20 distally diminishing denticles. Merus relatively narrow, with distolateral spine; flexor margin unarmed. Carpus with distolateral spine.

P1: Slender, [5.2]–5.6 × longer than carapace, with sparse long setae. Ischium with sharp dorsal spine, unarmed on ventral surface, with obsolescent subterminal spine on ventromesial margin. Merus subequal to length of carapace, with 3 spines somewhat distal to midlength (1 dorsal, 1 mesial, 1 ventromesial), and 4 spines on distal margin. Carpus proximally narrowed, [1.4]–1.5 × longer than merus; with 2 dorsal spines equidistant between proximal and distal ends, and 3 or 4 terminal spines (1 or 2 dorsal, 2 mesial). Palm medially broadened, more strongly so in paratype, 2.8–[3.7] × longer than broad, subequal to length of carpus, somewhat depressed (0.7 × as high as broad); proximally with a few denticle-like small spines, smooth elsewhere; mesial margin roundly ridged. Fingers strongly incurved distally and crossing when closed, somewhat gaping in both sexes; movable finger half as long as palm, opposable margin with low, blunt process at proximal third; opposable margin of fixed finger with lower process (obsolescent in male) distal to opposite process of movable finger.

P2–4: With sparse long setae, relatively thick mesio-laterally (0.8 × thicker than high). Ischia with 2 very small dorsal spines. Meri successively shorter posteriorly (P3 merus 0.9 × length of P2 merus, P4 merus [0.8]–0.9 × length of P3 merus); P2 merus [1.0]–0.9 × length of carapace, subequal to length of P2 propodus; P3 merus 0.9 × length of P3 propodus; P4 merus [0.7] × length of P4 propodus; length-breadth ratio, [4.1]–4.8 on P2, [3.3]–3.7 on P3, [3.0] on P4; dorsal margins with 5 spines on P2, 3 spines on P3, unarmed on P4 (where present, distalmost spine situated at distal end. Carpi subequal on P2 and P3, shorter on P4; carpus-propodus length ratio, 0.4 on P2–4, carpus-dactylus length ratio, 0.7–0.8 × on P2 and P3, [0.6] or 0.7 × on P4. Propodi shorter on P2 than on P3 and P4, 1.7 x longer than dactyli on P2–4; flexor margin nearly straight, with pair of slender terminal spines preceded by 5 or 6, 4, 3 or [4] spines on P2, P3, P4, respectively. Dactyli proportionately broad; flexor margin feebly concave in lateral view, with 10 or 11 sharp, relatively loosely arranged, very slightly inclined spines, ultimate spine shorter and more slender than penultimate.

Remarks. The new species strongly resembles U. minutus Benedict, 1902 in the arrangement of spines on the carapace lateral margin, the spination of P2–4, shape of the sternal plastron and preceding sternites, and the Mxp3 ischium bearing a spine on the distal end of the flexor margin. Uroptychus marissae is differentiated from U. minutus by the following: the rostrum is distinctly broader than long rather than longer than broad; the antennal scale terminates in the proximal third length of article 5, instead of reaching or slightly falling short of the distal end of article 5; the antennal flagellum consists of 6 instead of four segments, and is much longer instead of much shorter than the antennal article 4 and 5 combined, extending beyond the rostrum by its full length instead of terminating at most at the rostral tip; the P1 ischium bears a vestigial instead of distinct subterminal spine on the ventromesial margin; the P1 carpus is as long as instead of much shorter than the palm, and distinctly longer (1.4– 1.5 ×) instead of slightly shorter (0.90–0.96 ×) than the merus; the P2–4 are more slender than in U. minutus (length-breadth ratio, 4.1–4.8, 3.3–3.7, 3.0 on P2, P3, P4 respectively in U. marissae , versus at most 3.2 on P2, 2.7 on P3, 2.5 on P 4 in U. minutus ).

Uroptychus spiniger Benedict, 1902 , which keys out together with U. minutus (see Chace, 1942: 10), has additional morphological similarity in spination of the carapace lateral margin, Mxp3 and P2–4, but is clearly different in having the antenna with a much longer antennal scale extending far beyond the end of article 5 and the distal articles each bearing a strong distomesial spine, in having sternite 3 with a pair of spines on the anterior margin, and in having prominent spines on P1, all of these characters verified by examination of the holotype (male, 3.8 mm, USNM 7795).

Figures

FIGURE 4. Uroptychus marissae n. sp., A, C – E, G – J, male holotype 1.6 mm (USNM 1251916); B, F, female paratype 1.6 mm (USNM 1251917). A, carapace and anterior part of abdomen, dorsal. B, same. C, same, lateral. D, sternal plastron, with sternites 1 – 3 and basal parts of Mxp 1. E, right pleura of abdominal somites 2 – 5, dorsolateral. F, same. G, telson. H, right antenna, ventral. I, right Mxp 3, setae omitted, ventral. J, same, lateral. Scale bars: A – F, 1 mm; G – J, 0.5 mm.

FIGURE 5. Uroptychus marissae n. sp., A, B, C, male holotype 1.6 mm (USNM 1251916); D, female paratype 1.6 mm (USNM 1251917). A, P 1, dorsal. B, same, proximal part, ventral. C, same, mesial. D, P 1, dorsal. Scale bar: 1 mm.

FIGURE 6. Uroptychus marissae n. sp., male holotype 1.6 mm (USNM 1251916). A, right P 2, lateral. B, left P 2, distal part, setae omitted, lateral. C, right P 3, setae omitted. D, right P 4, lateral. Scale bars: 1 mm.