Gammarus setosus Dementieva, 1931

Vader, Wim & Tandberg, Anne Helene Solberg, 2019, Gammarid amphipods (Crustacea) in Norway, with a key to the species, Fauna norvegica 39, pp. 12-25 : 18

5. Gammarus setosus Dementieva, 1931

Synonym: Lagunogammarus setosus auct.

Description and illustrations: Stephensen 1935 -42, p. 321, fig. 41; Segerstråle 1947, p. 241, fig. 7; Christiansen 1965, fig. 3; Bousfield 1973, p. 50, pl. 1-2.

Biology: A mostly arctic marine, largely intertidal species. In the Arctic ( Weslawski 1994), and also in Iceland ( Ingolfsson 1977), this species is often found intertidally under stones, generally above the zone populated by G. oceanicus . In Newfoundland G. setosus is only found in the outlets of cool fresh-water streams in summer (V. Steele & Steele 1970), and this is precisely the biotope in which we have found this species in Finnmark, where it is found in the larger rivers, usually below the waterline.

Distribution in Norway: This is basically an Arctic species, and it has been reported from only a few places in Northern Norway (Malangen, Hammerfest, Tana) ( Vader 1977b); a record from the Oslofjord ( Stephensen 1935 -42, p. 323) we consider doubtful. The species has an amphi-atlantic, high northern distribution, and is common on Svalbard.

C. The Gammarus zaddachi group

The three species G. zaddachi , G. salinus and G. wilkitzkii appear to be closely related morphologically, zoogeographically and ecologically; however, the ‘under-ice high-arctic’ G. wilkitzkii seems quite different from the other two, that are confined to a quite restricted area in northwestern Europe: south to western France (Bretagne). All three are basically brackish water species. G. zaddachi and G. salinus are easily recognized compared to the species in groups A and B because of their colour pattern; they have a clear pattern of transverse dark stripes on a light brown background.