Metopa invalida Sars, 1892

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 : 12-13

Metopa invalida Sars, 1892

Metopa invalida Sars 1892: 267–69 , pl. 94–2

Metopa alderi (part)—Boeck 1871: pl. XVII fig 4 and 4k

Metopa invalida — Stephensen 1938: 176; Gurjanova 1951: 429, fig. 272; Dunbar 1954: 733

Material examined. Morphological examination: F13733 (coll G.O. Sars, no locality on label) female .

Type locality: probably sample F13732, coll G.O.Sars, locality Hammerfest .

See figures 24, 25, 26, 27 and 28.

Morphological redescription of material sampled and identified by original author.

Head ( Fig. 24 ): small and round; cephalic lobe rounded; eye large, 0.5x head length, round, well defined. Antenna 1 ( Fig. 25 ): short and mildly stocky; peduncle as long as flagellum, article 1 as long as article 2; flagellum 11-articulate, distal articles with 2 simple setae each; no accessory flagellum observed. Antenna 2 ( Fig. 24 ): slightly longer than antenna 1; peduncle 2x flagellum length, article 4 and 5 subequal; flagellum 6- articulate. Labrum ( Fig. 25 ): rounded. Mandible ( Fig. 25 ): palp 1-articulate, short and stubby, one simple short seta at apex; incisor serrate; lacinia mobilis weakly serrate but well defined; raker setae strong and cuspidate; no molar. Maxilla 1 ( Fig. 25 ): inner lobe small and rounded, one simple seta; outer plate distal margin flat, two long and one short cuspidate setae, two serrate setae, a row of 11 simple setae along inner margin; palp 1- articulate, one tooth and one cuspidate seta apically, distal margin serrate with simple setae in each nook, simple setae along margins. Maxilla 2 ( Fig. 25 ): slender; outer plate in normal position to inner plate; inner plate with six and outer plate with six setae each. Maxilliped ( Fig. 25 ): long and somewhat slim, but not as slim as those mentioned above; inner plates partially separate, with a rounded nook and three simple setae distally on each lobe; outer plate reduced; palp 4-articulate, inner two articles with minute setae along outer margin and simple setae along inner margin, article 3 with a cushion of short simple setae and a few pectinate setae at distal margin, article 4 lined with short simple setae along inner margin.

Pereon ( Fig 24 ): smooth. Pereopod 1 ( Fig. 26 ): simple; coxa subquadrate; basis elongate and slim; ischium subquadrate; merus suboval, cushioned with short simple setae along posterior margin and simple setae and type A setae along distal margin; carpus elongate subtriangular, long simple and type A setae along distal margin; propodus longer and slimmer than carpus, posterior margin lined with minute and longer simple setae, no palmar corner; dactylus 0.5x propodus length, curved, inner margin with some simple setae. Pereopod 2 ( Fig. 26 ): coxa suboval, covering coxa 1, directed forwards; basis linear; ischium and merus subquadrate; carpus cup-shaped subtriangular, cushioned with short, simple setae at posterior margin and lined with type A setae at distal margin; propodus subrectangular, elongate, palm oblique, weakly crenulate with a few short simple setae, hind margin 1.5x palm length, with sets of two simple setae; dactylus simple and curved, as long as palm. Pereopod 3 ( Fig 27 ): coxa subrectangular, with simple setae along posterior margin, slightly longer than coxa 2; rest of leg slim and simple; basis with several simple setae along both anterior and posterior margin; dactylus slim and simple, 0.4x propodus length. Pereopod 4 ( Fig. 27 ): coxa rounded triangular, large; rest of leg simple and about as thin as P3, more setae than P3; dactylus 0.5x propodus length, slim, curved and simple. Pereopod 5 ( Fig. 28 ): coxa small; basis slim, linear, lined with simple setae along both anterior and posterior margin; meral lobe 1/3 of carpus; simple setae along most of anterior margin of leg; dactylus 0.5x propodus length, curved and slim. Pereopods 6 and 7 ( Fig. 28 ): coxae small, coxa 6 posteriorly expanded; bases posteriorly expanded, lined with simple setae along anterior margins; meral lobes reaching 0.5x of carpus for both legs; dactyli slim and simple, 0.7x and 0.5x of propodus, respectively.

Urosome ( Fig. 24 ): smooth. Epimeral plate 3 ( Fig. 24 ): posterodistal corner right angled. Uropod 1 ( Fig. 28 ): longer than uropod 2; biramous; peduncle longer than rami, three simple setae along inner margin; rami subequal. Uropod 2 ( Fig. 28 ): a little longer than uropod 3; biramous; peduncle shorter than inner ramus, three simple setae along inner margin; outer ramus shorter than inner ramus, inner ramus with several simple setae along inner margin. Uropod 3 ( Fig. 28 ): uniramous; peduncle shorter than ramus, two simple setae along inner margin, peduncle wider than ramus; ramus 2-articulate, inner article slightly longer than outer article, inner article with one simple seta at distal margin. Telson ( Fig. 27 ): elongate with length 2.5x width; tip rounded; naked.

Sexual differences: no sexual differences found.

Distribution: North-Norwegian coast, among hydroids, Ungava Bay, see map Figure 65 F .

Ecology: among hydroids, 70–80 m depth, cold water.

The name invalida (weak/powerless) probably refers to the weak gnathopods.

Remarks. The fact that the mandible-palp is 1-articulate and short takes this out of the clear definition of Metopa , which includes specifically a 2–3 articulate mandible-palp ( Boeck, 1872; Barnard & Karaman, 1991). A species with a 1-articulated mandible palp, but else in all characters like a Metopa would fall into Stenula Barnard (1962) . As both the genrera Metopa and Stenula are being examined for their combined phylogeny (Tandberg & Vader in prep), a possible move of M. invalida will not be suggested here. Even though the probable type-material was not dissected for examination here, the dissected material was collected by the original author.

Figures

FIGURE 24. Metopa invalida Sars, 1892, female, 4 mm, F13733: whole animal. Scale bar is 0.5mm.

FIGURE 25. Metopa invalida Sars, 1892, female, 4 mm, F13733: antenna 1, labrum, mandible, maxilla 1, maxilla 2, maxilliped. All scale bars are 0.1 mm.

FIGURE 26. Metopa invalida Sars, 1892, female, 4 mm, F13733: gnathopod 1, gnathopod 2. Both scale bars are 0.1 mm.

FIGURE 27. Metopa invalida Sars, 1892, female, 4 mm, F13733: pereopod 3, pereopod 4, telson. All scale bars are 0.1 mm.

FIGURE 28. Metopa invalida Sars, 1892, female, 4 mm, F13733: pereopod 5, pereopod 6, pereopod 7, uropod 1, uropod 2, uropod 3. All scale bars are 0.1 mm.

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