Metopa gigas, Just, Jean, 2013

Just, Jean, 2013, Metopa gigas sp. nov. from southern Greenland, a giant among congeners (Crustacea, Amphipoda, Stenothoidae), Zootaxa 3641 (3), pp. 289-295 : 289-294

Metopa gigas sp. nov.

Figs 1–4

Type fixation. Holotype, ♀, here designated.

Etymology. The epithet is the Latin noun for Giant.

Material examined. Holotype, ♀, 19.0 mm, West Greenland, Godthaabsfjord [Kugssukfjord], approximately 64°N 52°W, ca. 300 m, ‘ Tjalfe’ stn 52, 15 June 1908, ZMUC CRU-20522.

Paratypes. Same data as holotype, ZMUC CRU-20523 (15 specimens, juveniles and immature). Southernmost Greenland: S of Akuliaruseq, 60°08.6’N 44°10.7’W, 400– 250 m, rectangular dredge on steep rock face with hydroids, Kap Farvel Expedition, stn 103, 17 August 1970, ZMUC CRU-20524 (1 ♀, 23 immature). Southernmost island in Toqulineq, 60°04.5’N 43°02.7’W, 240 m, stones, gravel, clay, Bryozoa, rectangular dredge, Kap Farvel Expedition, stn 136, 25 August 1970, ZMUC CRU-20525 (1 3, 19.1 mm). Off Sydprøven [Alluitsup Paa], 60°20’N 47°27’W, 120 m, on Hydroida, ottertrawl, ‘ Godthaab’ Expedition, stn 188, 10 October 1928, ZMUC CRU-20526 (1 specimen *). East Greenland: Scoresby Sund, Stewart Land, 70°30’N, 300 m, East Greenland Expedition 1900, 29 July 1900, ZMUC CRU-20527 (1 specimen *). Scoresby Sund, Kap (Cape) Tobin, 70°22’N 22°05’W, 108 m, stones, East Greenland Expedition 1900, 21 August 1900, ZMUC CRU-20528 (1 3, 19.2 mm, 3 immature*). East Greenland Expedition 1900, (no further data, but presumably Scoresby Sund area), ZMUC CRU-20529 (1 immature*). East Greenland Expedition 1900, (no further data, but presumably Scoresby Sund area), ZMUC CRU-20530 (1 immature*). West Greenland: Nordre Strømfjord, ca. 30 km from mouth of fjord, N of Holsteinsborg [Sisimiut], approximately 67°30’N 53°30’W, 200–240 m, V. Nordmann, 1911, stn 3C, ZMUC CRU-20531 (1 specimen *).

Note. Specimens in the ZMUC collections here marked * were reported as Metopa clypeata (Kr) by Stephensen (1931, 1944).

Description. (Based on holotype). Head length (tip of rostrum to pereonite 1) as pereonite 1 and half of 2 combined; interantennal lobe strongly projecting, broadly rounded; eyes small, round, occupying approximately 1/ 3 of head length level with eye; frons projection below the rostrum in a right angled blunt triangle between eye lobes, widely separated from irregularly rounded epistome projecting well beyond upper lip.

Pereonites dorsally with low, broad ‘saddle’ in posterior half, weak in 1 and 2, increasingly more pronounced in more posterior pereonites; pleonites with similar ‘saddle’. Pereonites 1–4 increasing in length, 5–7 of equal length, all slightly shorter than 4. Pleonites 1–3 of subequal length, all about as long as pereonite 7; pleonal side plate 1 ventrally rounded, 2 and 3 rectangularly pointed.

Coxal plate 2 roundedly pointed apex, with weak concavity posterodistally; plate 3 evenly convex distally; plate 4 as long as pereonites 2–5 combined along their ventral margins, 1.8 longer than mid depth; plates 5 and 6 with posterior lobe.

Antenna 1 as long as head, pereonites and pleonites 1 and 2 combined along dorsal curvature; peduncle articles 1 and 2 of equal length; flagellum of 36 articles, each with 2 short aesthetascs. Antenna 2 as long as head, pereonites 1–5 and half of 6 combined, peduncle articles 4 and 5 of equal length, flagellum 4/5 length of peduncle article 5, with about 11 article.

Left mandible lacinia mobilis serrate, nearly as broad as equally serrate incisor; body medially with ridge and low hump; palp of 1 article (probably damaged; see Remarks below). Right mandible incisor as in left; lacinia composed of 2 separate flattened setae; body medially with low hump carrying 5 short, stiff setae; palp of 2 articles, article 1 elongate with lateral row of simple setae; article 2 about 1/5 length of 1, with a few terminal setae. Maxilla 1 palp with row of 11 robust setae in distal half of medial margin and apically, distal surface with cover of small setae and setules; outer lobe with 7 smooth spine-setae. Maxilliped outer plate vestigial; inner plates fused with apical notch and small marginal setae.

Gnathopod 1 slender, merus projecting under carpus; carpus elongate, about twice as long as propodus, densely setose along posterior margin; propodus simple; dactylus short, with row of setae on posterior margin. Gnathopod 2 merus in lateral view with acutely pointed projection covering entire carpus and about 1/5 of propodus, with transverse rows of small robust setae along posterior margin, in medial view with rounded dorsal lobe with a few small robust setae; carpus dorsal margin with row of stridulating knobs, in medial view with anterodorsal acute projection, posterior lobe with fringe of simple setae; propodus as long as basis, slightly widening distally, palm convexly transverse, crenulated, posteriorly defined by deep notch and strong tooth.

Pereopod 3 thin, slightly longer than 4, with short simple setae only. Pereopod 4 robust, posterior margins of merus, carpus and propodus with a few transverse rows of small robust setae. Pereopod 5 basis rectilinear with row of long simple setae in proximal half of anterior margin; merus, carpus and propodus anterior margin with several transverse rows of small robust setae. Pereopods 6–7 basis posteriorly broadly expanded, basis of 6 anterior margin with row of small robust setae, of 7 with a few simple setae; merus, carpus and propodus of both armed as in pereopod 5.

Uropod 1 peduncle slightly longer than urosomite 1, dorsolateral margin with about 21 robust setae, dorsomedial margin with 7 robust setae; outer ramus 0.8 length of peduncle, with 4 dorsal robust setae, inner ramus as long as outer, smooth, both up-curved distally. Uropod 2 peduncle 0.8 length of uropod 1 peduncle, dorsolateral margin with 10 robust setae, dorsomedial margin with a few scattered robust setae; outer ramus 0.75 length of peduncle, slightly up-curved, dorsolaterally with 3 robust setae; inner ramus as long as peduncle, smooth, slightly up-curved distally. Uropod 3 peduncle 2.8 times longer than greatest lateral width, dorsolaterally with 4 robust setae, subequal in length to uropod 2 peduncle, with dorsoapical projection; article 1 of ramus about 2/3 length of peduncle, with dorsoapical group of small robust setae; article 2 of ramus about 4/5 length of article 1, tapering, smooth.

Telson oval, slightly broader in distal half, with 2 blunt robust setae each side in proximal half, single simple seta each side in distal half.

Size. Largest male, 19.2 mm; largest female, 19.1 mm.

Distribution. Southern Greenland, south of approximately 70°N on the west- as well as east coast; 120– 400 m.

Remarks. Males are similar to females. Immature specimens of about 8 mm and juveniles of 5 mm have antenna 1 as long relative to the body as in adults. Immature specimens have small dorsal saddles, while juveniles have only a small rounded bump at the presumptive place.

The palp of the left mandible in the large male from Kap Tobin (CRU-20528) is similar to the right one in the holotype ( Fig. 2 md mv r), and it has a setal row as in the right mandible. This indicates that the left mandible of the holotype has been damaged at some point.

Figures

FIGURE 1. Metopa gigas sp. nov. Holotype, Ƥ. c lv, head lateral view; gp 1, gnathopod 1; gp 2, gnathopod 2; l, left; lv, lateral view; mv, medial view. Habitus scale: 5 mm.

FIGURE 2. Metopa gigas sp. nov. Holotype, Ƥ. l, left; md mv, mandible medial view; mx 1 and 2, maxilla 1 and 2; mxp, maxilliped (reduced size compared with other mouthparts).

FIGURE 3. Metopa gigas sp. nov. Holotype, Ƥ. p 3 – p 7, pereopods 3 – 7.

FIGURE 4. Metopa gigas sp. nov. Holotype, Ƥ. up 1 – up 3, uropods 1 – 3; us, urosome; tel, telson.