Metopa aequicornis Sars, 1879

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 : 5-6

Metopa aequicornis Sars, 1879

Metopa aequicornis Sars 1879: 453 ; Sars 1885: 188, pl.15, fig. 5

Metopa aequicornis — Stebbing 1906: 180

Metopa aequicornis — Stephensen 1938: 174

Metopa aequicornis — Gurjanova 1951: 429–30, fig. 273

Material examined. Morphological examination: F1806 (det: G.O. Sars Station 343 Norwegian North Atlantic Expedition, 76°34’N, 12°51’E, 07.08.1874) Male. 6 mm. Holotype.

The specimen had been dried out some time during its museum-history, and was quite flat.

Type locality: St. 343 Norwegian North Atlantic Expedition : 76°34’N, 12°51’E, 1359 m , -1.2°C.

See figures 1, 2, 3, 4 and 5

Morphological redescription of male type material.

Head ( Fig. 1 ): epistome projected and rounded, cephalic lobe rounded; eye 1/4 of head length, round, well defined. Antenna 1 ( Fig. 2 ): long and slender, almost as long as body length; second peduncle article slightly longer than first; flagellum 17-articulate, with minute seta on the articles; no accessory flagellum observed. Antenna 2 ( Fig. 2 ): as long as A1; peduncle almost 3x length of flagellum; flagellum 12-articulate, naked. Labium ( Fig. 2 ): rounded with minute setae at distal edge. Mandible ( Fig. 2 ): mandibular palp 3-articulate, circular in cross-section, apical article well developed, middle article longer than first and third combined, long, thin, simple setae along middle and apical article; incisor and lacinia mobilis serrate and well developed; single row of raker setae; no molar. Maxilla 1 ( Fig. 2 ): inner plate with one simple distal seta; outer plate with four cuspidate setae, two of which marginally serrate, two teeth at apical edge, approximately 10 thin simple setae along inner margin; palp 1-articulate, reaching 1.5x length of outer plate, with nine simple setae and one tooth apically, and deep serrations along the apical-inner margin. Maxilla 2 ( Fig. 2 ): outer plate in normal position to inner plate; both plates with several simple setae (outer with 15 and inner with five). Labrum ( Fig. 2 ): rounded and smooth. Maxilliped ( Fig. 2 ): long and slim; inner plates separate, with few simple setae at distal margin; outer plate reduced, with a very small nob reaching less than 1/4 of first article of palp, which is 4-articulate; palp with several simple setae along inner margin of articles 1 and 2, article 3 with several simple and one type A seta ( Tandberg & Vader 2009) at distal margin, article 4 with a single row of short simple setae along inner margin.

Pereon: smooth. Pereopod 1 ( Fig. 3 ): subchelate; coxa rounded quadrate; basis linear, with a flat frontal margin with long simple setae; ischium subquadrate, with two simple setae distally; merus with posterodistal corner semi-free and with a row of long simple setae along distal margin; carpus subtriangular with a flat posterior margin lined with long simple setae; propodus subrectangular, slightly shorter and less broad than carpus, more than twice as long as broad, palm oblique with no distinct palmar corner, palm lined with short simple setae; dactylus inner margin with short simple setae, as long as palm. Pereopod 2 ( Fig. 3 ): coxa covering coxa 1, directed forwards; merus posterior margin lined with a few simple setae, distal margin with a row of simple setae; carpus subtriangular with stridulatory knobs along anterior margin and a row of simple setae along posterodistal margin; propodus subrectangular, palm almost transverse, with a strong tooth at palmar corner, palm crenulate, and with a few short plumose and a few short simple setae; dactylus curved and smooth, almost as long as palm, not reaching the tooth at palmar corner. Pereopod 3 ( Fig. 3 ): simple and slender; coxa subrectangular; dactylus 0.5x length of propodus, slim and simple. Pereopod 4 ( Fig. 4 ): simple and slender; coxa subtriangular; a few simple setae along posterior margin of merus, carpus and propodus; dactylus 0.3x length of propodus, slim and simple. Pereopod 5 ( Fig. 4 ): basis slender; meral lobe 1/4 of carpus; very few simple setae along anterior margin; dactylus slim and simple. Pereopods 6 and 7 ( Fig. 5 ): coxae small, coxa 7 subcircular; basis posteriorly expanded; meral lobe short, less than 1/3 of carpus; very few simple setae along anterior and posterior margins, dactyli simple.

Urosome ( Fig. 4 ): smooth. Epimeral plate 3 ( Fig. 4 ): posterodistal corner acute with rounded tip. Uropod 1 ( Fig. 5 ): longer than uropod 2; biramous; peduncle with several short simple setae, almost double length of rami, rami subequal in length; outer ramus with three small simple setae, inner ramus naked. Uropod 2 ( Fig. 5 ): longer than uropod 3; biramous; peduncle longer than rami, inner ramus longer than outer ramus; outer ramus with one small simple seta. Uropod 3 ( Fig. 5 ): uniramous; ramus with two articles, peduncle shorter than article 1; peduncle with four short simple setae, inner article of ramus with one tiny seta. Telson ( Fig. 5 ): rounded, tongue-shaped; three pairs of setules.

Sexual differences: only one specimen was found in the museums collections, this was a male.

Distribution: SV of Spitsbergen, deep basin (1360 m). Not registered from any other stations, see map Figure 63 A .

Ecology: the specimen was found in cold water (-1.2°C), on clay.

The name aequicornis refers to the antennae being of equal length.

Figures

FIGURE 1. Photo of Metopa aequicornis Sars, 1879, male, 6 mm, F1806 holotype (A). Photo of Metopa tenuimana Sars, 1892, 3 mm, female, F13730 syntype (B).

FIGURE 2. Metopa aequicornis Sars, 1879, male, 6 mm, F1806 (holotype): antenna 1, antenna 2, labrum, mandible, labium, maxilla 1, maxilla 2, maxilliped. All scale bars are 0.1 mm.

FIGURE 3. Metopa aequicornis Sars, 1879, male, 6 mm, F1806 (holotype): gnathopod 1, gnathopod 2, pereopod 3. All scale bars are 0.1 mm.

FIGURE 4. Metopa aequicornis Sars, 1879, male, 6 mm, F1806 (holotype): pereopod 4, pereopod 5, ursome. All scale bars are 0.1 mm.

FIGURE 5. Metopa aequicornis Sars, 1879, male, 6 mm, F1806 (holotype): pereopod 6, pereopod 7, uropod 1, uropod 2, uropod 3, telson. All scale bars are 0.1 mm.

FIGURE 63. Distribution map of A: Metopa aequicornis Sars, 1879 and B: Metopa affinis Boeck, 1871