The freshwater habitats (mires, streams, lakes, pools and wallows) on sub-Antarctic Marion Island were examined for invertebrates. Sixty-eight species were found, including 45 new records for the Island. Of these 56 were bona fide aquatic invertebrates, the rest being terrestrial or brackish interlopers that had fallen or been blown into the water. The aquatic species include five platyhelminthes, a gastrotrich, three tardigrades, 28 rotifers, six nematodes, two annelids and 11 arthropods. Most are familiar species that have been recorded on other sub-Antarctic islands. The invertebrate faunas of the various freshwater habitats were basically similar in species composition, with the abundances of particular species dependent upon the water body's size, distance from the sea and degree of eutrophication resulting from seal and seabird manuring.