A New Species of Acanthocephalus from New England Fishes, with Observations on Variability

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Abstract
Acanthocephalus jacksoni sp. n. is described on the basis of several hundred specimens collected from a variety of fresh-water fishes from numerous locations in Massachusetts and New Hampshire. Although highly variable, A. jacksoni differs from A. dirus, the only other species of the genus in North American fishes, by having fewer hooks per longitudinal row, larger hooks, and smaller embryos. It most resembles A. lucii, but A. jacksoni has smaller embryos and the hook roots lack the flattened triangular appearance of the hook roots of A. lucii. There was considerable variation in the number of longitudinal rows of hooks on the proboscis, the number of hooks per row, the size of the hooks, and the number of cement glands. In addition, there were incomplete rows of hooks, forked hooks, lobed and branched lemnisci, and nearly seven per cent of the males were monorchids. Although some of these variations seem to be related to host or geographic location there is so much overlap that it seems likely that all specimens represent a single, highly variable species.
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