A new species of coelozoic myxosporean, Alatospora merluccii n. sp., is described from the gall bladders of the hakes Merluccius australis and M. hubbsi caught on the Falklands Shelf and in Argentine and southern Chilean waters. The new species infected 13 of 113 M. australis examined (11.5% prevalence) but only one of 195 M. hubbsi (0.5% prevalence). Myxidium baueri Kovaleva and Gaevskaya 1982, is redescribed from the gall bladders of M. hubbsi (one of the type hosts) and M. australis (new host record). M. baueri infected 37 of 113 M. australis (32.7% prevalence) but only six of 195 M. hubbsi (3.1% prevalence). Apart from the spores of M. baueri from our material being slightly larger than in the original description, the only major anomaly between the two descriptions was in the number of spores in the pansporoblast, but we do not consider the differences sufficient to justify the erection of a new species for our material. The geographical distributions of infected fish suggest that both parasites are coldwater species with southern distributions in the study area.
