The freshwater sponge Anheteromeyenia ryderi (Potts) ( = Heteromeyenia ryderi Potts) has its main range in the eastern parts of North America, with one record from Central America. It is also represented in western parts of the British Islands, on the Faroes, and is now reported from three lakes in western South Norway. A description is given of some ecological factors in the Norwegian habitats such as the low calcium content and low pH. With the use of scanning electron microscopy details of the spicules appeared which were useful in species determination. These findings support the view that Anheteromeyenia pictovensis Potts cannot be ranked as a distinct species, but should be considered as a variety of A. ryderi. If A. ryderi is a very old species, its amphiatlantic distribution pattern may be explained by continental drift and/or Pre-Pleistocene land bridges. The species is probably easily transported by birds. There are arguments in favour of a more recent colonization of Europe by such transport, the European populations possibly having their origin in populations adapted to an oceanic climate in North America.