Acanthocephalus parksidei Amin, 1974, was recently described from 11 species of Wisconsin fishes. Considerable variation was observed in this acanthocephalan's body size, number and arrangement of proboscis hook, size of hooks, proboscis, proboscis receptacle, lemnisci, embryos, testes, and cement glands, and number of the latter two. Most of these variations were related to worm sex and age as well as host species. Structural variations in the shape and lobation of lemnisci, abnormalities in hooks and body wall, and changes associated with monorchidism in males were noted. The significance of the erection of this new taxon in relation to the taxonomic criteria applied to acanthocephalan species is discussed.