Two new species of the genus Sphaeromyxa (Myxosporea) from the gall bladder and one new species of the genus Eimeria (Coccidia) parasitizing the testes, are reported from engraulid fishes from the Argentinian shelf (including the Argentinean-Uruguayan Common Fishing Zone): Sphaeromyxa bonaerensis n. sp., found in Engraulis anchoita Hubbs & Marini, 1935 (argentine anchovy) (prevalence 0.2%) and in Anchoa marini Hildebrand, 1943 (anchovy) (prevalence 24.2%) caught in the Bonaerense region of the Argentinian Sea; Sphaeromyxa argentinensis n. sp. found in E. anchoita from all the sampled localities between 34 degrees S and 46 degrees S (prevalence 26.8%) and from A. marini at Mar del Plata coastal zone (prevalence 1.01%). Eimeria patagonensis n. sp. was found in E. anchoita living in the Patagonian region of the Argentine Sea (prevalence 0.45%). Details of some ultrastructural features of S. argentinensis are provided.