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Segerstråle, 1947

Urosome segments 1 to 3 with quite pronounced, rounded, dorsal humps; spine groups with an occasional seta. Epimeral plates 2 and 3 with the distal angle weakly produced, posterior margin with only one or two small setae. Head with the lateral lobes broadly truncated, post-antennal sinus deep; eyes moderately large, elongate kidney-shaped. Antenna 1 peduncle sparsely setose, peduncle article 1 with three or four ventral setal groups, article 2 with three or four setal groups, article 3 without or with only one setal group (excluding the apical setae); accessory flagellum about equal to the length of the peduncle article 1, a little longer than article 2, about 9 or 10-articulate. Antenna 2 peduncle with groups of long setae, flagellum setose, proximal articles with calceoli in male. Mandible palp article 1 devoid of setae, article 3 with two or three setal groups on the outer surface, ventral setae comb-like, not graduated. Male gnathopod 1 propodus with palm weakly sinuous, median spine well separated from the large group of angle spines. Male gnathopod 2 propodus much broader than in gnathopod 1 and the palm less oblique, median spine well separated from the angle spines, palmar margin weakly sinuous. Female gnathopods 1 and 2 propodus subrectangular, palm weakly oblique, margin about straight. Pereiopods 3 and 4 spinose and sparsely setose. Pereiopod 5 basis with the distal angle freely produced. Pereiopods 6 and 7 basis elongate, posterior margin with only short setules, distal angle not produced but with a pair of stout spines, merus and carpus with only few short setae on the posterior margin, anterior margin with more numerous setae, carpal setae longer than the spines, setae increasing in length distally on the appendage; in female pereiopods 6 and 7 very sparsely setose. Uropod 3 outer ramus much broader than the inner one, margins strongly spinose with groups of moderately elongate plumose setae; inner ramus little over three-quarters length of the outer one; rami less densely setose in female. Telson lobes with three apical spines, one or two subapical spines, one or two lateral spines, each group with occasional short seta.

Up to 27 mm in male, 22 mm in female.

Rather uniform grey, yellow or greenish brown, often darker in female, no distinct colour markings.

In coastal marine habitats, from mid-tide level to shallow subtidal, occasionally to depths of 25 metres; usually amongst algae; tolerates wide range of salinity and temperature.

Arctic Ocean, widespread; North Atlantic, American and European coasts, Norway and Bothnian Bay to the southern North Sea.

Gammarus oceanicus