Orchestia gammarellus (Pallas, 1766)
Orchestia gammarellus is an amphipod of the family Talitridae. General features of this family include a laterally compressed, arched body; a short Antenna 1 and long Antenna 2; well-developed eyes and pereiopods (walking legs); hopping locomotion; and the ability to survive exposure to air in beach wrack-lines and debris. Orchestia gammarellus has a squarish-oval, medium-sized eye. Antenna 1 is short, with its tip reaching the distal end of peduncle segment 2 of Antenna 2. The peduncle of Antenna 1 has 4 segments, and the flagellum has 4-5 segments. Antenna 2 is about 1/3 body-length. The peduncle is more robust in the male than female, and the flagellum is slightly shorter than the peduncle. In both sexes, Gnathopod 1 is much smaller than Gnathopod 2. The dactyl (segment 7) of Gnathopod 1 barely overlaps the palm. The propodus of Gnathopod 2 is greatly inflated, especially in the male. The dactylus is shorter than the palm. Pereiopods 3 and 4 are relatively short. Perieopods 5-7 are progressively longer, and their coxal plates larger. The abdominal side plates 2 and 3 have angular corners. The urosome segments are distinct. Uropods 1 and 2 are biramous, while Uropod 3 is uniramous, with the distal segment blunt and spine-like. The telson is spade-like, formed of two medially fused lobes with stout lateral and apical spines. Adult males reach 16-18 mm, while females reach 14 mm. The color ranges from greenish brown to reddish brown. This description is based on: Bousfield 1973 and Lincoln 1979.
Northwest Atlantic, Gulf of St. Lawrence to Gulf of Mexico (Bousfield 1973)
Northwest Atlantic, Casco Bay to Gulf of Mexico (Bousfield 1973)
Type species of a nearly cosmopolitan species complex, Gulf of St. Lawrence to Patagonia, range expansion in North Sea and Baltic, North Sea to South Africa (Bousfield 1973; Persson 2001; Spicer and Janas 2006). Populations in Japan, Australia, and Ascension Island-St. Helena have been described as separate species.