Observations on Polymorphus minutus (Goeze, 1782) (Acanthocephala) from a wildfowl reserve in Kent

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Abstract
Observations are described on Polymorphus minutus in its final and intermediate hosts from a wildfowl reserve in Kent. The appearance of the parasite in the reserve followed the alteration of the course of the River Darent, an operation which created a suitable habitat for the intermediate host, Gammarus pulex.The parasite has been found to occupy the same region of the intestine in the Mallard as in domestic ducks, but it occupies a more anterior region in the Tufted Duck. Worms of varying age have been shown to be present in natural infections of wildfowl.P. minutus and a cestode, Dicranotaenia coronula, appear to compete for attachment sites in the intestine of Mallard. This competition may be a factor which causes the attachment zone of P. minutus to be extended anteriorly.The presence of the parasite in the reserve appears to be causing the population of G. pulex to decrease.It is suggested from the observations made on the birds of the reserve, from the results of infecting domestic ducks and from a consideration of the list of final hosts of the parasite, that there exist strains of P. minutus, adapted to development in different species of birds.We wish to thank Dr P. Tate for helpful discussions, and Dr I. C. Williams, Department of Zoology, University of Hull, for the identification of the cestodes and criticism of the manuscript. Thanks are also due to Drs J. M. and D. L. Harrison, Mr G. Wallis and Mr A. Meikle for assistance with the population studies and the collection of some of the material.