Metopa alderii ( Bate, 1857 )

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 : 8-10

Metopa alderii ( Bate, 1857)

Montagua alderii Bate 1857: 137 ; Bate 1862: 57

Montagua alderi — Goës 1866: 522

Metopa spectabilis Sars 1879: 451-52 ; Sars 1883: 91; Sars 1885: 185, pl. 15, fig 4; Sars 1892: 251–52, pl. 87

Metopa alderi — Schneider 1891: 76

Metopa alderi — Sars 1892: 250–51, pl. 86

Metopa spectabilis — Reibisch 1905: 175, Brüggen 1907: 223–24; Tesch 1916: 330–31

Metopa alderi — Stephensen 1925: 65–66; Stephensen 1928: 160–62, fig. 30:7–8; Stephensen 1938: 170; Stephensen 1944: 57–58

Metopa spectabilis — Stephensen 1925: 66; Stephensen 1928: 162–63, fig. 30:1–6; Stephensen 1931: 183; Stephensen 1938: 171

Metopa spectabilis — Shoemaker 1930: 46; Schellenberg 1942: 119–120, fig. 97

Metopa alderi — Schellenberg 1942: 119, fig. 96

Metopa alderi — Dahl 1946

Metopa alderi — Gurjanova 1951: 423, fig. 264

Metopa spectabilis — Gurjanova 1951: 423, fig. 265

Metopa alderi — Dunbar 1954: 729–30; Oldevig 1959: 43; Bousfield 1973: 88; Lincoln 1979: 182, figs. 81a–c, 82a–i

Material examined. Morphological examination: F13756 (coll by G.O. Sars, Norv. occid.) female, 5 mm.

F13755 (coll by G.O.Sars, Norv. occid.) male, 5 mm.

Material from UNIS AB321 cruise 2009, Hinlopen: 79°35.37’N, 18°51.98’E, both male (5 mm) and female (6 mm) .

Type locality: coast of Northumberland .

Photo: F1804 (det: G.O.Sars, St 31, 343 Norwegian North Atlantic Expedition) Syntype of Metopa spectabilis .

See figures 9, 10,11, 12 and 13.

Morphological redescription of male and female material collected by Sars.

Head ( Fig. 9 ): Antenna 1 ( Fig. 10 ): short (male) to medium length (female), thin and naked; peduncle shorter than (female) or slightly longer than (male) flagellum; flagellum 5 (male) to 10 (female) articles, naked except for two terminal simple setae; no accessory flagellum observed. Antenna 2 ( Fig. 10 ): longer than

A1; peduncle 3x as long as flagellum, articles four and five subequal; flagellum 8 articles. Labium ( Fig. 10 ): rounded. Mandible ( Fig. 10 ): palp 3-articulate, article 2 longest, article 3 minute, cross-section circular, a few simple setae along margin of article 2 and one apical seta; lacinia mobilis and incisor serrate and well developed; raker setae plump and serrate; no molar. Maxilla 1 ( Fig. 10 ): inner plate narrow and elongate, one distal seta; outer plate square distally with one tooth, five cuspidate setae, one with serrations, a row of simple setae along inner margin; palp 1-articulate, distal margin serrate with five cuspidate setae. Maxilla 2 ( Fig. 10 ): outer plate in normal position to inner plate; inner plate with four and outer plate with eight simple setae apically. Maxilliped ( Fig. 10 ): long and slender; inner plates fused, but with a "keel" along the middle; outer plate reduced; palp 4-articulate, inner margin lined with longish simple setae, article 3 with a cushion of short simple setae at distal inner margin and two pectinate setae along distal margin, article 4 with a row of short simple setae along inner margin.

Pereon: smooth. Pereopod 1 ( Fig. 12 ): unclearly subchelate; coxa subtriangular, small, covered by coxa 2; basis linear, lined with simple setae at anterior margin; ischium quadrate; merus subtriangular, distally free, with a short-setaed cushion along posterior-distal margin and a row of simple and setae type A setae along distal margin; carpus triangular, posterior margin covered with simple and setae type A; propodus elongate rounded triangular, palm oblique, lined by tiny and a few larger simple setae, set off by a largish cuspidate seta at palmar "corner", hind margin "wavy" with few simple setae; dactylus curved, inner margin finely serrate, tip with several small simple setae. Pereopod 2 ( Fig. 11 ): coxa suboval, directed forwards; basis straight; ischium short and squarish; merus cup-shaped triangular; carpus cup-shaped triangular, a row of setae type A along distal margin, female with short setaed cushion along posterior margin; propodus subrectangular with a nearly transverse palm with a deep incision at lower half of palm (male) or subtriangular with an oblique palm with a smaller incision at lower part of palm (female) both palms slightly serrate and setaed; dactylus curved, with a flat inner margin set off with short setae, not reaching tooth at palmar corner. Pereopod 3 ( Fig. 12 ): coxa subrectangular, with a few setae along posterior margin; rest of leg slim and simple, few simple setae along anterior margin; dactylus smooth and curved. Pereopod 4 ( Fig. 13 ): coxa subtriangular; rest of leg simple, a bit more robust than P3, simple setae along both anterior and porserior margin; dactylus falcate. Pereopod 5 ( Fig. 13 ): coxa small, extended slightly posteriorly; basis linear, meral lobe 0.5x carpus length; short simple setae along anterior margin; dactylus falcate. Pereopods 6 and 7 ( Fig. 13 ): coxae small; bases posteriorly expanded; meral lobe about 0.5x of carpal length; P6 with a bit more and shorter simple setae than P7; dactylus falcate.

Urosome ( Fig. 9 ): smooth. Epimeral plate 3 ( Fig. 9 ): posterodistal corner right angled. Uropod 1 ( Fig. 13 ): longer than uropod 2; biramous; peduncle longer than rami; rami subequal, outer ramus slightly shorter than inner, both peduncle and outer ramus lined with short setae. Uropod 2 ( Fig. 13 ): longer than uropod 3; biramous; peduncle longer than rami, outer margin with small setae; outer ramus little longer than inner. Uropod 3 ( Fig. 13 ): uniramous; peduncle subequal to ramus, ramus with two articles, articles subequal; peduncle with five and inner article of ramus with one short setae. Telson ( Fig. 13 ): tongue-shaped, tip slightly pointed, length 2x width; two pairs of tiny setules.

Sexual differences: Gnathopod 2 in the male has a much wider and deeper excavation of the palm than in the female (see Fig. 11 ). Female size is larger than male, the body more "plump" and round. Antenna 1 is longer in relation to antenna 2 in female than in male.

Distribution: coast of Northumberland (type location), Wales, Iceland, Norwegian coast (west to north), Spitsbergen both southwestern coast and north-eastern sounds (Tandberg et al., in press), Murman coast, Helgoland, Skagerrak, Bohuslän, East Greenland, the Gulf of St Lawrence, Ungava Bay, Northern Coast of Maine, see map Figure 64 C .

Ecology: Sars (1892) mentions this species being found among hydroidae in colder waters. It has been found down to 50 m depth according to Stephensen (1938), but Lincoln (1979) has a depth range of 20– 750 m. Tandberg et al. (in press) found it living inside the mussels Musculus niger and M.discors , much like Metopa glacialis ( Vader & Beehler (1983); Tandberg et al. (subm)). It is also associated with medusae ( Vader, 1972).

The name alderii refers to J. Alder (Esq.) for whom Bate named the species.

Other material. The type-material from Sars of Metopa spectabilis has also been examined, the difference being in size, with the excavation of the palm of male gnathopod 2 being more pronounced. Material from Hinlopen strait collected 2009 has been examined, and was found in perfect accordance with the older material from Sars.

Remarks. Already Sars (1892) commented that his Metopa spectabilis was very close to Bates Metopa (Montagua) alderi , but the synonymization was not carried out until Dahl (1946) formalised it, discussing that M. alderi might be the younger/smaller form of the adult M. spectabilis .

Figures

FIGURE 9. Metopa alderii (Bate, 1857) photo of F1804 syntype of Metopa spectabilis: female (A), male (B).

FIGURE 10. Metopa alderii (Bate, 1857), female, 5 mm, F13756: antenna 1, antenna 2, labrum, mandible, maxilla 1, maxilla 2, maxilliped. All scale bars are 0.1 mm.

FIGURE 11. Metopa alderii (Bate, 1857), female, 5 mm, F13756: gnathood 2; male, 5 mm, F13755: gnathopod 2. Both scale bars are 0.1 mm.

FIGURE 12. Metopa alderii (Bate, 1857), female, 5 mm, F13756: gnathopod 1, pereopod 3. All scale bars are 0.1 mm.

FIGURE 13. Metopa alderii (Bate, 1857), female, 5 mm, F13756: pereopod 4, pereopod 5, pereopod 6, pereopod 7, uropod 1, uropod 2, uropod 3, telson. All scale bars are 0.1 mm.

FIGURE 64. Distribution map of C: Metopa alderii (Bate, 1857) and D: Metopa boeckii Sars, 1892