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Dahl, 1938

Body slender; urosome segments 1 to 3 with numerous elongate dorsal spines forming a transverse row. Epimeral plate 3 obtusely quadrate, posterior margin weakly convex with several small setules. Head with broad lateral lobes; eyes elongate, kidney-shaped. Antenna 1 slender, longer than antenna 2, peduncle articles 1 and 2 about equal in length, flagellum up to 45-articulate; accessory flagellum up to 9-articulate. Antenna 2 flagellum up to 25-articulate, densely setose; calceoli absent. Antenna 1 and 2 peduncle articles with groups of long ventral setae. Male gnathopod 1 propodus elongate oval, palm longitudinal with the median palmar spine well separated from the angle spines, proximal posterior margin sparsely setose. Male gnathopod 2 carpus equal to the length of the propodus, both densely setose, propodus subrectangular, palm oblique, concave, with close group of angle spines. Female gnathopod 1 propodus oval, setose, palm convex. Gnathopod 2 carpus a little longer than the propodus, both setose, propodus rectangular, palm transverse. Pereiopods 5 to 7 spinose; pereiopod 5 only with the basis freely produced distally. Male uropod 3 outer ramus elongate, slender, strongly spinose, inner margin with many long setae, outer margin with a few short setae. Female uropod 3 also spinose but with only few setae; plumose setae absent in male and female. Telson lobes with one lateral and three apical spines, and a pair of small dorsolateral plumose setae.

Up to 20 mm in male, female slightly smaller.

Pale brown to olive green often with a purple tinge; occasionally pink.

Intertidal, below mid-tide level on coarse gravel and shingle, often amongst algae, but not in presence of muddy deposits.

North Atlantic, American and European coasts; from Norway and Iceland to Brittany; widespread and frequently recorded.

Gammarus obtusatus