Paratenuisentis ambiguus, an acanthocephalan originating from North America,is an alien species parasitising the European eel Anguilla anguilla. It was first recorded in Lake Lebsko,on the central coast of Poland. The report gives morphometric measurements of male and female P. ambiguus from this locality. Because of the spread of the intermediate host Gammarus tigrinus andthe appearance of new adults in eels along the southern Baltic Coast, P. ambiguus is evidently able to complete its life cycle in Baltic coastal waters.
