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

Description:

Size: up to 30mm

Colour: pale pinkish/yellowish

Head longer than pereon segment 1; cephalic lobe broadly triangular, distally rounded; eyes red

Antenna 1 peduncle article 1 not produced anterodistally, accessory flagellum 6-articulate; antenna 2 length 1.3 x antenna 1

Coxa 1 anterior margin slightly concave, anteroventral corner produced and rounded; coxa 4 posteroventral lobe deep and strong; epimeral plate 3 with strong, blunt upturned tooth; urosomite 1 depressed dorsally

Gnathopod 1 subchelate, propodus subrectangular, length 2.5 x breadth, longer than carpus; gnathopod 2 subchelate, propodus triangular, distally widening, length 1.3 x breadth, palm straight or weakly concave; dactylus shorter than palm, strongly hooked, posterior margin smooth; pereopods 5-7 propodus anterior margin with paired long and short robust setae; uropod 3 outer ramus longer than inner ramus

Telson emarginated, weakly longer than broad, with 2 pair of simple setae

Habitat: soft bottom

Mobility: mobile

Feeding: predator and scavenger

Distribution: Arctic Ocean, East Siberian Seas, Laptev Sea, Kara Sea, Franz Josef Land, Spitsbergen, Ellesmere Island, Beaufort Sea, depths 5-175m, mainly found between 30-60m

Distribution in Svalbard's fjords:

References:

Gurjanova, E. F. 1951. Bokoplavy morjej SSSR I sopredel'nykh vod (Amphipoda - Gammaridea). Akad. Nauk SSSR, Opredel. Faune SSSR 41 , pp. 171-172.

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. 2000. Distribution patterns and feeding strategies of lysianassoid amphipods in shallow waters of an Arctic fjord. Pol. Polar Res 22 (3-4), 173-186.

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

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

Nygard, H. 2009. Life history of Onisimus caricus (Amphipoda: Lysianassoidea) in a high Arctic fjord. Aquat Biol 5 , pp. 63-74.

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 .

Stephensen, K. 1935. The Amphipoda of N. Norway and Spitsbergen with adjacent waters. Tromso Mus. Skr. 3(1) , p. 41.

Stephensen, K. 1944. The zoology of East Greenland . Amphipoda. Medd. om Gronland. 121 (14) , p. 18.

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