Metopa longicornis Boeck, 1871

Tandberg, Anne Helene S., 2010, A redescription of Metopa species (Amphipoda, Stenothoidae) based on the type material. 3. Natural History Museum, Oslo (NHM) 2465, Zootaxa 2465 (1), pp. 1-94 : 15-16

Metopa longicornis Boeck, 1871

Metopa longicornis Boeck 1871: 63 ; Boeck 1872:460–62, pl. XIX - 1

Metopa longicornis — Hansen 1888: 97, Tab. IV, fig. 1

Metopa longicornis — Sars 1892: 259–59, pl. 90-2

Metopa longicornis — Stephensen 1926: 68; Stephensen 1928: 167–68, fig. 31:13–15; Stephensen 1931: 188; Stephensen 1938: 174

Metopa longicornis — Gurjanova 1951: 426–27, fig. 268

Metopa longicornis — Dunbar 1954: 732; Shoemaker 1955: 20; Just 1980:48, fig. 46

Material examined. Morphological examination: F2362, (det: G.O. Sars, Nansen Expedition, 78°29’N, 136°E, 24.10.1893) female, 4.5 mm.

Type locality: Christianiafjord (Oslofjord).

See figures 33, 34, 35 and 36.

Morphological redescription of female specimen identified by Sars.

Head ( Fig. 33 ): small and rounded, cephalic lobe subacute; eyes small and round, well defined, 1/4 of head length. Antenna 1 ( Fig. 34 ): longer than antenna 2, slender; flagellum longer than peduncle, peduncle article 2 longer than article 1, article 3 shorter than both articles 1 and 2; flagellum broken in examined material, but in photographed specimens (from same tube of samples as dissected material), the flagellum consists of 13 articles; no accessory flagellum observed. Antenna 2 ( Fig. 34 ): also long and slender; flagellum slightly shorter than peduncle; peduncle articles 4 and 5 subequal in length; flagellum with eight articles, each with two short simple setae distally. Labrum ( Fig. 34 ): evenly rounded. Mandible ( Fig. 34 ): palp 3-articulate, third article tiny, second article long, first article as long as diameter, cross-section of palp circular, one seta at each of articles 2 and 3; incisor narrow and crenulate; lacinia mobilis similarly narrow but serrate; raker setae serrated and cuspidate; no molar. Maxilla 1 ( Fig. 34 ): inner lobe elongate, one simple seta at distal margin; outer lobe broad and with straight distal margin, armed with three long and two short cuspidate and two long serrate setae, inner margin lined with simple setae; palp 1-articulate, with a tooth at apex, and a slightly serrate inner distal margin with a simple seta in each nook, minute simple setae along outer margin. Maxilla 2 ( Fig. 34 ): outer plate in normal position to inner plate; inner plate with three long and four short setae and outer plate with seven long and seven short simple setae. Maxilliped ( Fig. 34 ): long and narrow; inner plates fully separate, one tiny seta at distal margin of each lobe; outer plate completely reduced; palp 4-articulate, with very few setae before distal margin of article 3, which is cushioned with short simple setae, and inner margin of article 4, which is lined with simple setae.

Pereon ( Fig. 33 ): smooth. Pereopod 1 ( Fig. 35 ): simple; coxa subquadrate; basis straight and naked; ischium subquadrate; merus oval and boat-shaped, cushioned with short simple setae along posterior margin, with three long simple setae at distal margin; carpus elongate, length 2x width, lined with simple setae at posterior margin; propodus simple, four very thin and simple setae along posterior margin; dactylus almost as long as posterior margin propodus, with a sharp curve at tip, smooth. Pereopod 2 ( Fig. 35 ): coxa oval, covering coxa 1, directed forwards; basis slender and straight; ischium subquadrate; merus subtriangular, one type A seta at distal margin; carpus subtriangular, with a cushion of simple short setae along posterior margin and a row of simple setae and setae type A along distal margin; propodus subrectangular, palm oblique, weakly crenulate with alternating tiny and small simple setae, palmar corner set off by two longer cuspidate setae, palm subequal in length to hind margin; dactylus as long as palm, smooth and slightly curved at tip. Pereopod 3 ( Fig. 35 ): coxa subrectangular; basis slim and straight, rest of leg slim and simple; dactylus 0.4 length of propodus, simple and slighty curved. Pereopod 4 ( Fig. 36 ): coxa rounded triangular; rest of leg slim and simple, with a few simple setae along both anterior and posterior margins; dactylus 0.5x propodus length, smooth and slightly curved. Pereopod 5 ( Fig. 36 ): coxa small; basis slender and straight; rest of leg simple and narrow; dactylus short, curved. Pereopods 6 and 7 ( Fig. 36 ): coxae small; bases posteriorly extended; meral lobe 0.15x and 0.3x of carpal length, respectively; simple setae along both anterior and posterior margins of both legs; dactyli 0.5x propodus length in both legs, very weakly curved, and smooth.

Urosome ( Fig. 33 ): smooth. Epimeral plate 3 ( Fig. 33 ): posterodistal corner acute. Uropod 1 ( Fig. 36 ): longer than uropod 2; biramous; peduncle 2x length of rami, rami subequal. Uropod 2 ( Fig. 36 ): longer than uropod 3; biramous; peduncle longer than rami; outer ramus longer than inner. Uropod 3 ( Fig. 36 ): uniramous; peduncle shorter than ramus; ramus 2-articulate, first article longer than second. Telson ( Fig. 35 ): elongate, length almost 3x width, tip rounded, 3 pairs of tiny cuspidate setae.

Sexual differences: no sexual differences described.

Distribution: Norwegian coast (Oslofjord (type locality) and Lofoten islands), NE Greenland, W Greenland, Ungava Bay, Davis strait, Alaska, Laptev Sea, see map Figure 66 H .

Ecology: has been found at 30–110 m depth.

The name longicornis refers to the antennae being long.

Figures

FIGURE 33. Metopa leptocarpa Sars, 1883, photo of F2362 female 4.5 mm (A), male (B).

FIGURE 34. Metopa longiocornis Boeck, 1871, female, 4.5 mm, F2362: antenna 1, antenna 2, labrum, mandible, maxilla 1, maxilla 2, maxilliped. All scale bars are 0.1 mm.

FIGURE 35. Metopa longicornis Boeck, 1871, female, 4.5 mm, F2362: gnathopod 1, gnathopod 2, pereopod 3, telson. All scale bars are 0.1 mm.

FIGURE 36. Metopa longicornis Boeck, 1871, female, 4.5 mm, F2362: pereopod 4, pereopod 5, pereopod 6, pereopod 7, uropod 1, uropod 2, uropod 3. All scale bars are 0.1 mm.

FIGURE 66. Distribution map of G: Metopa leptocarpa Sars, 1883 and H: Metopa longicornis Boeck, 1871