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Leach, 1815

Description:
Urosome segments 1 to 3 each with numerous dorsal spines forming a continuous transverse row. Epimeral plate 3 triangularly produced, posterior margin with several short setules. Head with the lateral lobes broadly truncated; eyes elongate and weakly kidney-shaped. Antenna 1 peduncle article 1 longer than article 2, article 3 about half the length of article 2, flagellum about two and a half times the length of the peduncle and up to 50-articulate; accessory flagellum well developed, 7 to 9-articulate. Antenna 2 flagellum equal to the length of the peduncle, densely setose, calceoli absent. Male gnathopod 1 propodus narrowly oval, palm almost longitudinal, median palmar spine not clearly separate from the angle spines, proximal posterior margin of the propodus with groups of long setae and solitary characteristic short stout spines. Male gnathopod 2 propodus shorter and broader than in gnathopod 1, palm oblique, median palmar spine not separated from the angle spines. Female gnathopod 1 propodus smaller and much less elongate than in male, but marginal spines and setae similar. Female gnathopod 2 palm almost transverse, spines and setae similar to male. Pereiopods 3 and 4 weakly setose in male, more densely setose in female. Pereiopods 5 to 7 spinose; pereiopod 5 only with the posterodistal angle freely produced. Male uropod 3 outer ramus densely setose along both margins but without plumose setae; inner ramus also spinose and setose. Uropod 3 in female less densely setose than in male, inner margin with a few plumose setae, spines elongate. Telson lobes each with a small group of lateral and apical spines and a few short setae, and a pair of small dorsolateral plumose setae.

Size:
Up to 25 mm in male, up to 20 mm in female.

Colour:
Dark green, occasionally with reddish or yellowish markings.

Habitat:
Intertidal, upper shore, typically on more sheltered beaches beneath algae on stones and shingle often with some sand or muddy deposits, less common on clean sand and shingle; tolerates reduced salinities; locally abundant.

Distribution:
North-East Atlantic; European coasts from Norway and Iceland to the north coast of Portugal; widespread and very frequently recorded.

Gammarus marinus