Metopa propinqua 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 : 17-19

Metopa propinqua Sars, 1892

Metopa propinqua Sars 1892: 264–65 , pl. 93-1

Metopa propinqua — Stebbing 1906: 174; Brüggen 1909

Metopa propinqua — Metopa propinqua Stephensen 1926: 67 ; Stephensen 1928: 170–71, fig. 32:7–9; Stephensen 1938: 168–69;

Metopa propinqua — Shoemaker 1930: 263; Shoemaker 1955: 22

Metopa propinqua — Gurjanova 1951: 434–35, fig. 280; Dunbar 1954: 725–27, fig. 7

Metopa propinqua — Oldevig 1959: 45; Bousfield 1973: 289; Lincoln 1979: 190, figs. 81g, 86a–h

Material examined. Morphological examination: F13711 (coll: G.O.Sars, Trondheimsfjord) ovigerous female, 2.5 mm. Syntype .

Photo: F13711, syntype .

Type locality: Trondheimsfjord (at Bejan or Rødberget), Norway .

See figures 41, 42, 43, 44 and 45.

Morphological redescription of female type material.

Head ( Fig. 41 ): small and rounded, cephalic lobe rounded; eyes small and round, less than 1/3 of head length. Antenna 1 ( Fig. 42 ): thin, half body length; peduncle 0.7x flagellum length, article 1 as long as articles 2 and 3 together; flagellum 12-articulate, a minute seta at each article; no accessory flagellum observed. Antenna 2 ( Fig. 42 ): as slender as antenna 1, slightly shorter than antenna 1; peduncle 1.2x flagellum, articles 4 and 5 subequal in length; flagellum with nine articles, each with a small simple seta. Labrum ( Fig. 42 ): rounded. Mandible ( Fig. 42 ): palp 2-articulate, round in cross-section, narrow, first article about as long as wide, second article almost 4x length of first, one simple seta at distal end; incisor and lacinia mobilis sharply serrate; raker setae with serrate edges; no molar. Maxilla 1 ( Fig. 42 ): inner lobe small, narrow, one simple seta at apex; outer lobe with flat distal margin, four cuspidate setae and one type A seta; palp 1-articulate, tooth at distal margin, slightly serrate inner margin with one simple seta in each nook. Maxilla 2 ( Fig. 42 ): outer plate in normal position to inner plate, inner plate with 10 and outer plate with 14 setae. Maxilliped ( Fig. 42 ): long and slim; inner plates fully separate, one minute seta at each distal margin; outer plate reduced; palp 4- articulate, article 3 with a cushion of short simple setae at distal inner margin and some long simple and pectinate setae at distal margin; article 4 lined with short simple setae at inner margin, curved (the illustration shows this a bit stronger than in reality, this is an artefact of the orientation of the mouthpart on the microscopic slide).

Pereon ( Fig. 41 ): smooth. Pereopod 1 ( Fig. 43 ): simple; coxa small and subquadrate; basis slim and straight; ischium subquadrate; merus subtriangular, with posterior margin cushioned with simple setae, distal margin lined with longer simple and pectinate setae; carpus elongate, posterior margin with long simple and pectinate setae; propodus 0.8x carpal length, simple, less wide than carpus, narrowing at distal end, posterior margin with long simple setae; dactylus strong, 0.7x propodus length, inner margin crenulate, lined with simple setae, curved at tip. Pereopod 2 ( Fig. 43 ): coxa suboval, directed forwards, covering coxa 1; basis slim and straight; ischium subquadrate; merus spoon-shaped and slightly elongate with a few long simple setae at posterior margin; carpus subtriangular, carpal lobe wide and free, posterior margin cushioned with short simple setae, distal margin lined with setae type A and simple setae; propodus subtriangular, longer than wide, palm oblique, slightly crenulate, set with simple setae, palmar corner clearly set off by two thick and long setae, hind margin longer than palm; dactylus as long as palm, curved, flat smooth inner margin. Pereopod 3 ( Fig. 43 ): coxa subrectangular; basis slim; meral lobe 0.2x carpal length; rest of leg slim and simple; propodus lined with thin setae along anterior margin; dactylus long and slim, 0.7x propodus length. Pereopod 4 ( Fig. 44 ): coxa subtriangular, distal margin sinuate; basis slim and straight; meral lobe 0.3x carpal length; rest of leg simple with short simple setae along posterior margin; dactylus with serrate inner margin, slightly curved, 0.6x length of propodus. Pereopod 5 ( Fig. 44 ): coxa small, slightly extended posteriorly; basis narrow and straight, with a flat posterior margin; meral lobe 0.7x carpal length; rest of leg simple, sets of type B setae ( Tandberg & Vader 2009) along anterior margin; dactylus slim, 0.6x propodus length, sharp notch at tip. Pereopods 6 and 7 ( Fig. 44 ): coxae small; bases expanded posteriorly, P7 basis rounded; meral lobes 0.8x or as long as carpus respectively; both legs with short simple setae along both anterior and posterior margins; dactyli slim, curved at tip, which have notches, 0.7x propodus length in both legs.

Urosome ( Fig. 45 ): smooth. Epimeral plate 3 ( Fig. 45 ): posterodistal corner slightly flared right angle, weakly rounded. Uropod 1 ( Fig. 45 ): longer than uropod 2; biramous; peduncle with flat inner margin lined with short setae, as long as rami; rami subequal, outer ramus with few simple setae at proximal margins. Uropod 2 ( Fig. 45 ): longer than uropod 3; biramous; peduncle with flat inner margin lined with short simple setae; outer ramus shorter than inner. Uropod 3 ( Fig. 45 ): uniramous; peduncle shorter than ramus, slightly wider, simple setae along inner margin; ramus 2-articulate, articles subequal in length, inner article with two simple setae. Telson ( Fig. 43 ): length more than 2x width, rounded tip, three pairs of thick setae.

Sexual differences: Brüggen (1909) described the male gnathopod 2 propodus as subrectangular, palm almost transverse, slightly crenulate, with a deep notch before palmar corner, producing a strong tooth at corner, and dactylus inner margin with minute setae. He further described the anterior margin of carpus as "sehr fein gesagt", a character that also Dunbar (1954) found in his male specimens, but in the examined female specimen from Sars there are no stridulation ridges. No other sexual differences recorded.

Distribution: Norwegian coast, North Sea, Bohuslän, Firth of Forth, Barents Sea, Kara Sea, Ungava Bay, Gulf of St Lawrence, Alaska, see map Figure 67 J .

Ecology: has been found on Thujaria , and often together with Cressa dubia Bate 1862 and often in subzero temperatures. The depth ranges are noted as between 50 and 130 m.

The name propinqua refers to this species being close to other Metopa . Sars (1892) mentioned this species to be M. sinuata , with similarities especially in the shape of coxa 4; at the same time there are clear differences in the shape of the antennae, the second gnathopods, the merus of P3 and the strong setae on uropod 3 and telson.

Figures

FIGURE 41. Metopa propinqua Sars, 1892, photo of F13711, syntypes, female 2.5 mm (A), male (B).

FIGURE 42. Metopa propinqua Sars, 1892, ovigerous female, 2.5 mm, F13711 (syntype): antenna 1, antenna 2, labrum, mandible, maxilla 1, maxilla 2, maxilliped. All scale bars are 0.1 mm.

FIGURE 43. Metopa propinqua Sars, 1892, ovigerous female, 2.5 mm, F13711 (syntype): gnathopod 1, gnathopod 2, pereopod 3, telson. All scale bars are 0.1 mm.

FIGURE 44. Metopa propinqua Sars, 1892, ovigerous female, 2.5 mm, F13711 (syntype): pereopod 4, pereopod 5, pereopod 6, pereopod 7. All scale bars are 0.1 mm.

FIGURE 45. Metopa propinqua Sars, 1892, ovigerous female, 2.5 mm, F13711 (syntype): epimeral plates, urosome, uropod 1, uropod 2, uropod 3. All scale bars are 0.1 mm.

FIGURE 67. Distribution map of I: Metopa palmata Sars, 1892 and J: Metopa propinqua Sars, 1892