Metopa borealis Sars, 1883

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 : 11-12

Metopa borealis Sars, 1883

Metopa borealis Sars 1883: 91 , fig. 4; Sars 1892: 254–55, pl. 89–1

Metopa borealis — Hansen 1888: 91–92, pl. III-4

Metopa borealis — Reibisch 1905: 32; Chevreux & Fage 1925: 126–27, fig. 124

Metopa borealis — Stephensen 1926: 69; Stephensen 1928: 166–67, fig. 31:7–8; Stephensen 1938: 175

Metopa borealis — Gurjanova 1951: 432–33, fig. 277

Metopa borealis — Bousfield 1973: 298; Lincoln 1979: 184, figs. 81f, 83a–g

Material examined. Morphological examination: F13834 (coll G.O.Sars, Hjelmeland) female 4.5 mm and male 4 mm.

Photo: F13738 (coll G.O.Sars Norv. Occid) Syntype .

Type locality: west Norway .

See figures 19, 20, 21, 22 and 23.

Morphological redescription of male and female material collected and identified by author.

Head ( Fig. 20 ): small and rounded, epistome flat; eyes 0.3x head length, round, well defined. Antenna 1 ( Fig. 20 ): short and stout; slightly shorter than antenna 2, little more than 1/4 of body length; peduncle short, article 1 as long as articles 2 and 3 combined; flagellum almost double length of peduncle, 11 articles; no accessory flagellum observed. Antenna 2 ( Fig. 20 ): slimmer than antenna 1; peduncle 1.5–2x length of flagellum, articles four and five subequal in length; flagellum consisting of eight articles, one simple seta at apex. Labrum ( Fig. 20 ): rounded. Mandible ( Fig. 20 ): palp 2-articulate, inner article short and subquadrate, article 2 suboval, few simple setae, palp cross-section oval; incisor and lacinia mobilis serrate and well developed, raker setae cuspidate; no molar. Maxilla 1 ( Fig. 20 ): inner plate small and rounded, one simple seta; outer plate oval, distal margin with five thick simple setae and one tooth, a row of thin simple setae along inner margin; palp 1-articulate, distal margin coarsely serrate, with few short simple setae. Maxilla 2 ( Fig. 20 ): outer plate in normal position to inner plate; inner plate with five and outer plate with six long simple setae. Maxilliped ( Fig. 20 ): long and slender; inner plates fullly separate, two simple setae apically; outer plate reduced; palp 4-articulate, thinly setaed along inner margin, article 4 lined with a row of simple setae along inner margin.

Pereon ( Fig. 19 ): smooth. Pereopod 1 ( Fig. 21 ): simple; coxa small, subcircular; basis linear; ischium subquadrate; merus subtriangular, distally free, a row of simple setae and setae type A at distal margin; carpus subrectangular, several simple seate along posterior margin; propodus with flat posterior margin, no palmar corner, subequal in length to carpus, but less wide; dactylus simple, thin, straight. Pereopod 2 ( Fig. 21 ): coxa subrectangular, covering coxa 1, directed forwards; basis simple and linear; ischium subquadrate; merus oval, cup-shaped; carpus triangular, cup-shaped, with a line of simple setae along distal margin; propodus subrectangular, palm oblique, serrate and lined with simple setae, palmar corner set off by small tooth, hind margin longer than palm; dactylus simple and curved, smooth. Pereopod 3 ( Fig. 22 ): coxa suboval; basis linear, few simple setae along lower anterior margin; rest of leg slim and simple; dactylus simple and curved, reaching 0.5x propodus. Pereopod 4 ( Fig. 22 ): coxa rounded triangular; rest of leg slim and simple, few simple setae along posterior margin of propodus; dactylus simple and curved, 0.5x propodus. Pereopod 5 ( Fig. 22 ): coxa small, weakly extended posteriorly; basis slender; meral lobe reaching 0.5x carpus length; dactylus slightly curved and slender, 0.5x propodus. Pereopods 6 and 7 ( Figs. 22 and 23 ): coxae small; bases posteriorly extended; meral lobes reaching 0.7x and 0.6x of carpal length respectively, both meri lined with simple setae posteriorly; dactyli simple and curved, reaching 0.6x and 0.5x propodus length; few simple setae along both legs.

Urosome ( Fig. 19 ): smooth. Epimeral plate 3 ( Fig. 19 ): posterodistal corner right angled. Uropod 1 ( Fig. 23 ): longer than uropod 2; biramous; peduncle longer than rami, six cuspidate setae along proximal part of peduncle; rami subequal, outer ramus with two and inner ramus with one cuspidate setae. Uropod 2 ( Fig. 23 ): longer than uropod 3; biramous; peduncle slightly longer than rami; inner ramus shorter than outer ramus. Uropod 3 ( Fig. 23 ): uniramous; peduncle slightly shorter and thicker than ramus, one cuspidate seta at distal margin; ramus 2-articulate, inner article longer than outer article, one small cuspidate seta on each article. Telson ( Fig. 23 ): tongue-shaped, curled up a little along the edges in the weak copy of a boat-shape; one pair of minute cuspidate setae.

Sexual differences: no sexual differences observed.

Distribution: Gulf of St. Lawrence, north-east Greenland, coast of Norway, eastern Murman coast, North Sea, Scotland, see map Figure 65 E .

Ecology: it is registered at localities of 9–180 m depth ( Lincoln (1979) mentions it only down to 50 m), in cold water. Stephensen (1928) mentions it being found on fine sand.

The name borealis refers to the the northern distribution of the species.

Figures

FIGURE 19.Metopa borealis Sars, 1883, photo of F13738 syntype, female 4 mm (A), male 4 mm (B).

FIGURE 20. Metopa borealis Sars, 1883, female, 4.5 mm, F13834: labrum, mandible; male, 4 mm, F13834: head, mandible, maxilla 1, maxilla 2, maxilliped. All scale bars are 0.1 mm.

FIGURE 21. Metopa borealis Sars, 1883, female, 4.5 mm, F13834: gnathopod 1, gnathopod 2. All scale bars are 0.1 mm.

FIGURE 22. Metopa borealis Sars, 1883, female, 4.5 mm, F13834: pereopod 3, pereopod 4, pereopod 5, pereopod 6. All scale bars are 0.1 mm.

FIGURE 23. Metopa borealis Sars, 1883, female, 4.5 mm, F13834: pereopod 7; male, 4mm, F13834: uropod 1, uropod 2, uropod 3, telson. All scale bars are 0.1 mm.

FIGURE 65. Distribution map of E: Metopa borealis Sars, 1883 and F: Metopa invalida Sars, 1892