The Eoacanthocephala of North America, including the Description of Eocollis arcanus, New Genus and New Species, Superficially Resembling the Genus Pomphorhynchus

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Abstract
EOCOLLIS arcanus* (order Neoacanthocephala) from Lepomis macrochirus and Pomoxis nigro-maculatus of southern Illinois is described and compared with Pomphorhynchus which it superficially resembles. The narrow neck-like structure and inflated bulb posterior to the proboscis are modifications of the trunk, not of the praesoma as are the similar structures in Pomphorhynchus. Six genera of Neoacanthocephala (Neoechinorhynchus, Gracilisentis, Tanaorhamphus, Octospinifer, Eocollis, Atactor-hynchus) are known from fishes of N. Amer., most spp. occurring in families of fishes distinctive of this continent. Only Neoechinorhynchus is common to Europe and North America. A key to the 6 genera is given. In the Eoacanthocephala, the Gyracanthocephala are regarded as more generalized and more primitive than the Neoacanthocephala. Of the former, 3 genera (Pallisentis, Neosentis, Acanthosentis) occur in the Orient while but a single genus (Pandosentis in S. Amer.) is found in the New World. The Neoacanthocephala have become diversified along with the development of the peculiarly distinctive families and genera of N. American fishes. It is postulated that an ancestral stock intermediate between present-day cestodes and acanthocepahalans lived in the earliest fishes or possibly in arthropods from which the first fishes acquired the worms which ultimately became the Acanthocephala. By interaction of genetic and environmental factors, the Acanthocephala have undergone evolution and speciation parallel with the main currents of vertebrate evolution.

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