Metopa affinis Boeck, 1871

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 : 6-8

Metopa affinis Boeck, 1871

Metopa affinis Boeck 1871: 142–43

Metopa affinis — Sars 1892: 260–61, pl. 91, fig. 2

Metopa affinis — Stebbing 1906: 176

Metopa affinis — Stephensen 1926: 70; Stephensen 1928: 168, fig. 31: 16–19; Stephensen 1938: 172

Metopa affinis — Gurjanova 1951: 421–22, fig. 262

Material examined. Morphological examination: F13832 (coll: A. Boeck, rev. G.O.Sars, no locality) male .

This specimen was not registrered in type collection, but is the only specimen of this species in the collections, and is collected by the original author. The specimen was already dissected.

Type locality: probably Christianiafjord (Oslofjord), SE Norway .

See figures 6, 7 and 8.

Morphological redescription of probable male type material.

Head: not present in the tube with the dissected specimen. Antenna 1 ( Fig. 6 ): broken in specimen. Naked, peduncle articles 1 and 2 equal size, flagellum broken; no accessory flagellum observed. Antenna 2 ( Fig. 6 ): peduncle double length of flagellum, peduncle article 4 and 5 equal length; flagellum 6-articulate, each article with two small setae. Mandible ( Fig. 6 ): palp 2-articulate (no inner article), fat, but with circular cross-section. The mandible palp was broken in the dissected specimen. Incisor and lacinia mobilis serrate and well developed; no molar. Maxilla 1 ( Fig. 6 ): inner plate with one simple seta; outer plate with three simple, three pectinate and one cuspidate setae, six simple setae along inner margin; palp 1-articulate, a little longer than outer plate, four simple longer setae and two shorter, one tooth at apical margin. Maxilla 2 ( Fig. 6 ): outer plate in normal position to inner plate; both plates with simple setae (outer with five and inner with four long and three short). Maxilliped ( Fig. 6 ): long and slim; inner plate fully separated, one single seta at the apical margin; outer plate reduced; palp 4-articulate with a few setae along inner margin of article 1 and 2, article 3 with a "cushion" of setae at tip, article 4 with a single row of setae along inner margin.

Pereon: specimen in tube was dissected before the present examination, but earlier illustrations show this as smooth. Pereopod 1 ( Fig. 7 ): subchelate; coxa subquadrate; basis linear; merus distally free, posterior margin cushioned with short simple setae and distal margin lined with simple and pectinate setae; carpus slender, a few simple setae; propodus as long as but more slender than carpus (propodus length 4x width), palm transverse, palmar corner rounded, palm naked; dactylus curved, as long as palm, simple setae on anterior margin. Pereopod 2 ( Fig. 7 ): coxa covering coxa 1, directed forwards, subrectangular, naked; basis linear; ischium subrectangular; merus triangular with one long and one short simple seta; carpus short, cupshaped, with a cushion of simple setae at posterior margin and a row of seta type A ( Tandberg & Vader 2009) along distal margin; propodus subrectangular, a little longer than broad, palm nearly transverse, smooth with simple setae, a clear tooth at palmar corner; dactylus smooth and weakly curved, as long as palm. Pereopod 3 ( Fig. 7 ): coxa subrectangular, one small simple seta at distal margin; basis linear, slightly curved; rest of leg slim and simple, very few simple setae; dactylus simple and very little curved. Pereopod 4 ( Fig. 7 ): coxa triangular; rest of leg simple, slightly thicker than P3 and a few more simple setae; dactylus with a little notch at tip. Pereopod 5 ( Fig. 8 ): coxa small, produced a little anteriorly; basis slender with a little widening at distal end; meral lobe 1/3 carpus length; few simple setae in pairs along anterior margin of carpus and propodus; dactylus simple and smooth. Pereopods 6 and 7 ( Fig. 8 ): coxae small, coxa 6 with a small production towards posterior part of basis; bases posteriorly expanded, naked; meral lobes small, reaching 1/3 and 1/4 of carpal length respectively; dactyli long and curved (dactylus of P7 broken in specimen).

Urosome: specimen was dissected before this examination, but earlier illustrations show this as smooth. Epimeral plate 3: not present in the tube of dissected pieces. Uropod 1 ( Fig. 8 ): biramous, naked, peduncle longer than rami, rami subequal, inner ramus longer than outer, but broken in the present material. Uropods 2 and 3: were not present in the tube with the dissected specimen, but according to Sars (1892) uropod 3 has a "somewhat lamellar" peduncle, and the length should be about the same as that of uropod 2. Telson: was sadly also not present in the tube, Sars (1892) describes this with length 2x width, rounded.

Sexual differences: Sars (1892) suggests that the second gnathopod is of slightly different form in females, but does not elucidate what this difference consists of. He does not give any other examples of sexual differences.

Distribution: Oslofjord, west Norway, Lofoten islands (north Norway). See map Figure 63 B .

Ecology: no ecological information is known about this species.

Remarks. The name affinis refers to it looking very much like closely related species, a fact Sars found "inappropriate" as he thought this species to be most distinct from all other known Norwegian species ( Sars, 1892).

Sars made, however, after examining the specimens that both Boeck and Hansen had collected, the suggestion that Metopa latimana Hansen (1888) was the same species as Boeck’s M. affinis . If this should be accepted, M. affinis should also occur in Greenland, where Hansen found his species. This view was, however, contested by Stephensen (1931, 1938), who claims Hansens specimen of M. latimana not to be identical with M. affinis ; in that case M. affinis does not occur in Greenland. Sars noted that Hansens specimen "agreed closely in all essential characteristics", but also that - as Hansen had commented to him - there was "a slight difference in the form of the gnathopoda", a problem he explained with the examined specimens from Hansen and Boeck being of different sexes. Stephensen (1931) comments that M. affinis is "rather closely allied" to M. latimana but not the same species, citing Hansens words about the gnathopods, highlighting the propodus of gnathopod 1 of M. latimana to have "a rather broad oblique palm" and the propodus of gnathopod 2 to be "somewhat longer and narrower with the palm not dentate". Stephensen examined the type specimen of M. latimana (the only specimen Hansen had collected) and made the first illustrations of M. latimana . Hansens type specimen was examined recently, but only gnathopods 1 and 2 and a head without mouthparts were found, the original slides were sadly not found ( Tandberg & Vader 2009), gnathopods 1 and 2 were found to be in perfect accordance with the drawings of Stephensen (1931).

When comparing the new illustrations and observations of Boecks specimen of M. affinis with both new illustrations of what has been found of M. latimana and Stephensens illustrations and Hansens descriptions of M. latimana the propodus of gnathopod 1 is longer and a little narrower in M. affinis than in M. latimana , both having a very short smooth palm, but the palm of M. affinis seems to be slightly more transverse than that of M. latimana , interestingly Sars (1892) illustrated the gnathopod 1 as even narrower, and with no visible palm, he calls this part "nearly linear in form" and does also in his text not mention the palm. Gnathopod 2 propodus is shorter and wider in the examined specimen of M. affinis than in M. latimana , and the tooth at the palmar corner is more pronounced. The coxa is also slightly more broad in M. affinis than in M. latimana . Pereopod 3 seems, based on the drawings in Stephensen (1931), to be more narrow and elongate both in coxa and dactylus in M. latimana than in M. affinis , pereopod 7 basis is more rounded in M. affinis and uropod 1 in M. affinis is missing the rather conspicuous cuspidate seta at the distal margin of the peduncle that M. latimana is illustrated with, but in the text Stephensen claims that uropods 1 and 2 do not have spines. It does, therefore, seem quite unclear if the two species should be synomymised or not, and the discussion should be ended by finding the rest of the type for M. latimana , if no fresh specimens can be found to test molecular characters. Without an examination of the mouthparts of M. latimana it is not possible to go further than to accept Stephensens claim that they are two different species.

From the note by Sars that the type from Boeck was a male, and the fact that only one specimen was in the Oslo collection noted as collected by Boeck and examined by Sars, we propose this specimen to be moved to the type collection as the probable holotype for this species. The type locality in that case is "Christianiafjord" (Oslofjord) .

Figures

FIGURE 6. Metopa affinis Boeck, 1871, male, F13832: antenna 1, antenna 2, mandible, maxilla 1, maxilla 2, maxilliped. All scale bars are 0.1 mm.

FIGURE 7. Metopa affinis Boeck, 1871, male, F13832: gnathopod 1, gnathopod 2, pereopod 3, pereopod 4. All scale bars are 0.1 mm.

FIGURE 8. Metopa affinis Boeck, 1871, male, F13832: pereopod 5, pereopod 6, pereopod 7, uropod 1. All scale bars are 0.1 mm.

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