Suborder: GAMMARIDEA  Latreille, 1802
Infraorder: Gammarida  Latreille, 1802
Superfamily: Lysianassoidea  Dana, 1849
Genus: Onisimus Boeck, 1871  

Description:

Size: up to 14mm

Colour: pale reddish-yellow

Head deeper than long; lateral cephalic lobe broad, subacute; eyes bright red

Antenna1 short, peduncle article 1 robust, not produced anterodistally, accessory flagellum 6-segmented, flagellum 15-18-articulate; antenna 2 length 1.2 x antenna 1

Coxa 1 large, anterior margin concave, anteroventral corner produced; coxa 4 with moderate posteroventral lobe; epimeral plate 3 with slightly upturned tooth

Gnathopod 1 subchelate, propodus subrectangular, length 1.9 x breadth, clearly longer than carpus; gnathopod 2 minutely subchelate with weakly developed palm; uropod 3 peduncle short, rami lanceolate, inner ramus about 0.8 x outer ramus

Telson cleft less than 30%, with 2 apical setae on each lobe

Habitat: mixed vegetated bottom, sand, stones, shells, gravel

Mobility: mobile

Feeding: opportunistic predator and scavenger

Distribution: cold North Atlantic and Atlantic Arctic, entire arctic coast of Russia east to the Chukchi Sea, cold eastern waters of Canada south to Nova Scotia; typically collected from shallow waters, depth range 2-70m

Distribution in Svalbard's fjords:

References:

Berge, J., Vader, W., Johnsen, J. R. 2007. Studies on the genus Onisimus Boeck, 1871 (Crustacea, Amphipoda, Uristidae) II. The barentsi and edwardsii groups. Zootaxa 1410 , pp. 55-68.

Bryazgin, V. 1997. Diversity, distribution and ecology of benthic amphipods (Amphipoda, Gammaridea) in the Barents Sea sublittoral. Pol. Polar Res. 18(2) , pp. 89-106.

Gurjanova, E. F. 1951. Bokoplavy morjej SSSR I sopredel'nykh vod (Amphipoda - Gammaridea). Akad. Nauk SSSR, Opredel. Faune SSSR 41 , pp. 162-163.

Kaczmarek, H ., Włodarska-Kowalczuk, M., Legeżyńska, J ., Zajączkowski, M . 2005. Shallow sublitoral macrozoobenthos in Kongsfjord, West Spitsbergen, Svalbard. Pol. Polish Res. 26 (2) , pp. 137-155.

Legeżyńska , J., Węsławski, JM., Presler, P. 2000. Benthic scavengers collected by baited traps in the high Arctic. Polar Biology 23 , pp. 539-544.

Legeżyńska, J. 2008. Food resource partitioning among Arctic sublittoral lysianassoid amphipods in summer. Polar Biology 31 , pp. 66-670.

Lowry, J. K., Stoddart, H. E. 1993. The Onisimus problem (Amphipoda, Lysianassoidea, Uristidae). Zoologica Scripta 22 (2) , pp. 167-181.

Nygard, H. 2011. Scavenging amphipods in the high Arctic : Studies of benthic and sympagic amphipods in the genera Onisimus and Anonyx . Doctoral thesis, University of Tromso .

Sars, G. O. 1890-1895. An account of the Crustacea of Norway with short descriptions and figures of all the species. vol. I: Amphipoda, Cammermeyers, pp. 105-106, pl. 36.

Stephensen, K. 1923. Crustacea Malacostraca. V (Amphipoda I). Dan. Ingolf Exped. 3 (8) , pp. 44-45.

Stephensen, K. 1935. The Amphipoda of N. Norway and Spitsbergen with adjacent waters. Tromso Mus. Skr. 3(1) , pp. 35-36.

Stephensen, K. 1944. The zoology of East Greenland . Amphipoda. Medd. om Gronland. 121 (14) , p. 16.

Szaniawska, A., Wołowicz, M. 1986. Changes in the energy content of common species from Hornsund, Southwest Spitsbergen . Polar Res 4 , pp. 85-90.

Węsławski, J. M. 1990. Distribution and ecology of South Spitsbergen coastal marine Amphipoda (Crustacea). Pol. Arch. Hydrobiol. 37 (4) , pp. 503-519.

Węsławski, JM ., Legeżyńska , J. 2002. Life cycles of some Arctic amphipods, Pol. Polar Res. 23 (3-4), pp. 253-264.