Two subterranean freshwater amphipod species were recently discovered in Iceland, Crangonyx islandicus and Crymostygious thingvallensis. These species are found within the volcanic active zone in the groundwater system and genetic patterns within C. islandicus have shown that it has survived repeated glaciations in Iceland. Nothing is known of the ecosystem these amphipods inhabit but presence of ciliate epibionts in different stages as cysts and phoronts, were observed on specimens from Þingvallavatn, Klapparós in Melrakkaslétta and at Sandur in Aðaldal. Analysis of the 18S ribosomal DNA sequence suggest that the sequences belong to a previously unsequenced species, most related to members of the genus Gymnodinioides, group Apostomatida. Gymnodinioides spp. are well known to be exuviotrophic crustacean parasites where the phoront stage is a nonfeeding stage. These phoronts were found almost exclusively ventrally in sheltered locations on the amphipods; the most common location beeing the first and second joint on pereopod 3-5 and pleopod 1-3. This indicates a preferance for location sheltered from possible grooming activity of the amphipods. A further study of ciliate variation living as epibionts or parasites on groundwater amphipods from N-America and Slovenia revealed distinct groups of ciliates on the different species.