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(Linnaeus, 1758)

Urosome segments 1 to 3 with very prominent angular dorsal humps, spine groups with few setae. Distal angle of epimeral plates 2 and 3 acutely produced, posterior margin with several short setules. Head with the lateral lobes sloping forwards, upper angle produced, post-antennal sinus shallow; eyes moderately large, kidney-shaped. Antenna 1 peduncle sparsely setose, article 1 without or with one ventral setal group, article 2 with one to two setal groups. article 3 without or with 1 setal group (excluding apical setae); accessory flagellum elongate, longer than the peduncle article 1, about 8 to 15-articulate. Antenna 2 peduncle setose, flagellum with caleoli in male on proximal articles. Mandible palp article 1 without setae, article 3 with one to three setal groups on the outer surface, ventral setae comb-like and graduated, becoming shorter proximally. Male gnathopod 1 propodus with the palm sinuous, a large flask-shaped median spine separated from the graduated angle spines, also four or five inner angle spines, proximal posterior margin with six to eight setal groups. Male gnathopod 2 propodus much broader than gnathopod 1 and the palm less oblique, a large flask-shaped median spine separated from the graduated angle spines, also two or three inner angle spines. Female gnathopod 1 propodus suboval, palm oblique; gnathopod 2 propodus elongate rectangular, palm transverse. Pereiopod 3 merus anterior margin with two setal groups each with one spine, posterior margin with about eight setal groups, carpus without anteromarginal setae, posterior margin with setae increasing in length distally. Pereiopod 4 merus with two setal groups on the proximal third of the anterior margin. Pereiopod 5 basis less than one and a half times as long as wide, distal angle freely produced. Pereiopod 6 basis with the posterior margin weakly convex. Pereiopod 7 basis slightly more than one and a half times as long as wide, distal angle not produced but with a pair of slender spines, posterior margin weakly angular, setae on the merus and carpus less than twice the length of the associated spines. Uropod 3 rami about equal in length, margins strongly spinose and with plumose setae. Telson lobes with three apical spines and a few short setae. One subapical spine and seta, and one to three lateral spines with few setae.

Up to 33 mm in male, about 20 mm in female.


It typically occurs from the low intertidal to about 30 metres: restricted to fully marine habitats.

North-East Atlantic. Åland, Norway and Iceland to Portugal. Widespread and frequently recorded, locally very common.

Gammarus locusta