Adult males of Gammarus pulex may reach a total length of 21 millimetres (0.83 in), while females only grow to 14 mm (0.55 in). The adults have a robust appearance; they are typically greyish with markings in dark brown or green.
The name Rivulogammarus has been used for a part of the genus Gammarus when it is split into smaller genera, and G. pulex has sometimes been called Rivulogammarus pulex. This name is, however, invalid under the International Code of Zoological Nomenclature, since G. pulex is the type species of the genus Gammarus, and the genus that contains it must therefore be named Gammarus.
Gammarus pulex (Linnaeus). Introduced into Northern Ireland in 1958-59, since when it has expanded its range to become the dominant amphipod there, replacing G. duebeni celticus in Lough Neagh and River Lagan. Now also found in small numbers in River Liffey and lower R. Boyne, Republic of Ireland. Its competitive interactions have been studied by J. Dick, among others. A similar replacement of G. duebeni by G. pulex has been reported in Brittany by A. Dunn.
Other sequences that do not yet meet barcode criteria may also be available.
GGAGCTTGGGCTAGTGTTGTTGGCACTTCCATA---AGAGTAATTATTCGTTCAGAGCTAAGTAGACCAGGTAATTTAATCGATGAT---GACCAACTGTATAACGTCATAGTCACCGCTCACGCTTTTGTTATAATTTTTTTTATAGTTATGCCTATTATAATTGGGGGTTTCGGAAATTGATTAGTACCTTTAATA---TTAGGTAGACCTGATATGGCTTTCCCGCGAATAAACAATATAAGATTTTGACTTTTACCTCCTTCCCTAACACTTCTGCTTATAAGTAGTATAGTAGAAAGAGGGGTAGGAACAGGGTGAACGGTGTACCCACCGTTAGCAGGTATTTCAGCTCACGGAGGCGGAGCTGTAGACTTG---GCTATTTTCTCATTACATCTGGCAGGAGCCTCCTCTATCCTAGGTGCCATTAATTTTATCTNTACTGTAATCAATATACGTAGACCTGGTATATCTATAGACCAAACACCTCTTTTTGTTTGGTCTGTCTTTATCACAGCTATCTTACTCCTCTTATCCTTACCTGTTTTAGCCGGG---GCTATCACAATACTCCTGACAGACCGTAACTTAAATACTTCTTTCTTTGACCCGAGCGGCGGAGGAGATCCTATTTTATACCAA -- end --