Details are given of Porterinema fluviatile from freshwater habitats in The Netherlands; experiments with cultured material are described and the Dutch algae are compared with previously published records. It is suggested that a freshwater record of Apistonema pyrenigerum from England (Belcher 1959) and a species of Apistonema described from the Neusiedler See, A. expansum Geitler 1970, actually represent material of Porterinema fluviatile.