The intertidal and nearshore Nereididae of the Falkland Islands are detailed and a new species of Gymnonereis
described. The new species, Gymnonereis tenera
sp. n., is the first record of the genus for the Falkland Islands. It is, so far, only known from a few intertidal locations in fine and muddy sands. Main distinguishing characters are: jaw teeth absent (in adults), 3 papillae in Area V-VI, falcigers absent, second ventral cirrus present throughout. Nereis atlantica
McIntosh, 1885, known only from the description of a single specimen and one doubtful record from the Falkland Islands, is reviewed and transferred to Perinereis
on the basis of the presence of shield-shaped bars in Area VI of the proboscis and the absence of notopodial falcigers. A key to all seven species discussed is provided.