Generally similar to Gammarus zaddachi but the setation less pronounced. Urosome segments 1 to 3 with weakly rounded dorsal humps, spine groups with few short setae. Epimeral plates 2 and 3 acute distally, posterior margin with only a few small setules. Head with broadly truncated lateral lobes, post-antennal sinus deep; eyes moderately large, elongate kidney-shaped. Male antenna 1 peduncle moderately setose, peduncle article 1 with about six ventral setal groups, article 2 with five or six setal groups, article 3 with two or three setal groups (excluding the apical setae); accessory flagellum equal to the length of the peduncle article 2, 5 to 9-articulate; small male specimens with fewer setal groups. Male antenna 2 with numerous groups of long setae, calceoli present in male, present or absent in female. Female antenna 2 peduncle article 4 with five to eight setal groups.
Mandible palp article 1 with one to four apical setae, article 3 with three to five setal groups on the outer surface, ventral seta irregular. Male gnathopod 1 propodus with the palm weakly sinuous, median palmar spine well separated from the large group of angle spines, proximal posterior margin with about six setal groups. Male gnathopod 2 propodus broader than in gnathopod 1 and the palm less oblique, median palmar spine well separated from the angle spines. Female gnathopod 1 propodus oval, palm convex, oblique; female gnathopod 2 propodus subrectangular, palm almost transverse. Pereiopods 3 and 4 setose, setae often longer than the associated spines. Pereiopod 5 basis with the posterodistal angle freely produced; pereiopods 6 and 7 basis elongate, posterior margin with short setae, distal angle not produced but with a pair of spines and few short setae, merus and carpus with setae on the posterior margin not longer, or only very slightly longer, than the associated spines. Uropod 3 inner ramus about one-tenth shorter than the proximal article of the outer ramus, margins with spines and plumose setae. Telson lobes with three apical, one subapical and one or two lateral spines, each group with few setae, may be slightly longer than the associated spines.
Up to 22 mm in male, 17 mm in female.
Brownish or greenish brown with transverse bands.
A brackish-water species less tolerant of very low salinities than Gammarus zaddachi and therefore found with a more seaward range; only occasionally these two species are found together.
North-West Europe from the English Channel to the Baltic.