Metopa palmata 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 : 16-17

Metopa palmata Sars, 1892

Metopa palmata Sars 1892: 272–73 , pl. 96–2

Metopa palmata — Stephensen 1931: 182; Stephensen 1938: 170

Metopa palmata — Gurjanova 1951: 420, fig. 259

Material examined. Morphological examination: F13739 (coll: G.O.Sars, Hammerfest) male. Holotype.

Already dissected by Sars, no specimen to calibrate size against.

Type locality: Hammerfest , north Norway .

See figures 37, 38, 39 and 40.

Morphological redescription of male type material.

Head ( Fig. 37 ): small; cephalic lobe rounded, and an extra lobe produced somewhat in front of antenna 2 peduncle article 2; eyes large, 1/2 of head length, rounded, defined. Antenna 1 ( Fig. 37 ): thickset; peduncle slightly shorter than flagellum, article 1 longer than articles 2 and 3 together; flagellum 14-articulate with short simple setae; no accessory flagellum observed. Antenna 2 ( Fig. 37 ): longer and thinner than antenna 1; peduncle longer than flagellum, article 5 slightly longer than article 4; flagellum 10-articulate, two simple setae on each article. Labrum ( Fig. 37 ): rounded. Mandible ( Fig. 37 ): palp 1-articulate, circular in crosssection, four simple setae along palp; incisor and lacinia mobilis (right mandible) serrate; raker setae flat with serrated tips; no molar. Maxilla 1 ( Fig. 38 ): inner lobe small and narrow, one simple seta; outer lobe with flat distal margin, seven cuspidate and six simple setae; palp 1-articulate, one tooth, five cuspidate setae, three long simple setae. Maxilla 2 ( Fig. 37 ): outer lobe in normal position to inner lobe; inner lobe with 17 and outer lobe with 13 setae. Labium ( Fig. 37 ): rounded. Maxilliped ( Fig. 38 ): small and slender; inner plates fully separate, three simple setae at distal margin; outer plates reduced; palp 4-articulate, third article with a cushion of short simple setae at inner distal margin, fourth article lined with short setae at inner margin, few simple setae along inner margin.

Pereon: the specimen was dissected by G.O.Sars, and so the pereon was not observed. From the illustrations in Sars (1892), the pereon is smooth. Pereopod 1 ( Fig. 38 ): simple; coxa small and subquadrate; basis narrow and linear; ischium subrectangular; merus elongate and narrow; carpus elongate, 1.5x propodus length; propodus narrow and linear, elongate; dactylus boat-shaped, lined with simple seta around edge, length 1.5x width, depth 0.5x width. Pereopod 2 ( Fig. 39 ): coxa much larger than coxa 1, suboval, three simple setae along posterior margin, directed forwards, and so probably covering coxa 1; basis linear; ischium and merus subtriangular, lines of simple setae along distal margins; carpus short, a row of simple setae and type A setae along distal margin; propodus subrectangular, length 1.3x width, palm transverse, smooth and armed with long simple setae, palmar corner rectangular, hind margin 2x palm length, a brush of simple setae along posterodistal margin; dactylus strong and smooth, almost as long as palm, and folding in over the side of propodus before palmar corner. Pereopod 3 ( Fig. 39 ): coxa subrectangular, three simple setae along posterior margin; basis slightly curved and not expanded; meral lobe 0.2x carpus length; rest of leg simple; dactylus slim and curved, 0.4x propodus length. Pereopod 4 ( Fig. 39 ): coxa subtriangular, large; rest of leg more stocky than that of P3; meral lobe 0.3x carpus length; carpus and propodus with brushes of 2–3 short simple setae along posterior margins; dactylus stocky and curved, 0.6x propodus length, distal inner margin serrate. Pereopod 5 ( Fig. 39 ): coxa small, slightly extended posteriorly; basis not expanded and straight, lined with minute simple setae along posterior margin; meral lobe 0.8x propodus length; merus, carpus and propodus lined with minute simple setae along anterior and posterior (merus) margins; dactylus slightly curved, tip with extra notch, length 0.5x propodus. Pereopods 6 and 7 ( Fig. 40 ): coxae small, coxa 6 sligthly extended posterodistally; bases expanded anteriorly, subcircular; meral lobes as long as (P6) or 1.3x (P7) that of carpal length, dactyli with notch at distal margin, slightly curved, 0.4x and 0.5x propodus length respectively.

Urosome: from Sars (1892) this is smooth. Epimeral plate 3 ( Fig. 40 ): posterodistal corner rounded sharp angle, approximately 60°. Uropod 1 ( Fig. 40 ): approximately as long as U2 (from Sars (1892) it is much longer than U2); biramous; peduncle with a flat inner margin, longer than rami, armed with 11 simple setae along the edges of inner margin; outer ramus minutely longer than inner, two simple setae, inner ramus naked. Uropod 2 ( Fig. 40 ): longer than U3; biramous; peduncle with flat inner margin, armed with five simple setae, longer than rami; rami subequal, outer ramus with two simple setae, inner ramus naked. Uropod 3 ( Fig. 40 ): uniramous; peduncle shorter than ramus, armed with three simple setae along inner margin, broader than ramus, a minute flare at distal margin; ramus 2-articulate, inner article longer and broader than outer margin, two distal setae, outer article naked. Telson ( Fig. 40 ): length 1.75x width, tip rounded, three pairs of cuspidate setae.

Sexual differences: no sexual differences described, in all very few specimens described. Sars (1892) only saw one "probably not fully mature" male, which is what was examined here.

Distribution: Northern Norway and West Iceland, see map Figure 67 I .

Ecology: The species has only been found at Hammerfest and Iceland.

The name palmata ("webbed") is not commented by Sars, but it is very probable this is a comment on the dactylus of pereopod 1.

Remarks. As with Metopa invalida we suggest this species might be moved closer to Stenula , since the mandible palp is 1-articulate. The boat-shaped dactylus of pereopod 1 is also supporting a move of this species to another genus. As with M. invalida this suggestion will wait until the phylogenetic analysis of the genera Metopa and Stenula (Tandberg & Vader in prep).

Figures

FIGURE 37. Metopa palmata Sars, 1892, male, F13739 (holotype): head, labrum, mandible, labium, maxilla 2. All scale bars are 0.1 mm.

FIGURE 38. Metopa palmata Sars, 1892, male, F13739 (holotype): maxilla 1, maxilliped, gnathopod 1. All scale bars are 0.1 mm.

FIGURE 39. Metopa palmata Sars, 1892, male, F13739 (holotype): gnathopod 2, pereopod 3, pereopod 4, pereopod 5. All scale bars are 0.1 mm.

FIGURE 40. Metopa palmata Sars, 1892, male, F13739 (holotype): pereopod 6, pereopod 7, epimeral plates, uropod 1, uropod 2, uropod 3, telson. All scale bars are 0.1 mm.

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