Acanthocephalus parksidei sp. n. (Acanthocephala: Echinorhynchidae) from Wisconsin fishes.

Acanthocephalus parksidei sp. n. is described from over 4,000 specimens recovered from 11 fish hosts in the Pike River, southeastern Wisconsin. A parksidei is a highly variable acanthocephalan which appears to present an intermediate form between the only 2 other members of the same genus, A. dirus and A. jacksoni, described from North American freshwater fishes. It is structurally similar to the larger A. dirus but is separated from it primarily by having fewer proboscis hook rows and hooks per row. It is separated from A. jacksoni on the basis of its slender body form, relatively larger size of male reproductive system in proportion to body size, as well as other features. It differs from the larger European A. lucii by having smaller proboscis hooks, different hook root shape, smaller proboscis receptacle, and smaller embryos.