Musculium transversum (Say, 1829) (Bivalvia, Sphaeriidae) in Nederland opnieuw levend aangetroffen

Once more Musculium transversum living in the Netherlands. Musculium transversum (Say, 1829) is a native of North America first recorded for Europe in the British Isles in 1856 and now widely distributed in England and Wales. In 1954 a second European population was discovered in Lake IJsselmeer near Amsterdam in the Netherlands. Since no further finds were made, this population must be considered lost. In 2000 a population was reported from NW France. The present article describes a new Dutch population in a brook named Drentse Aa near Groningen, which has lived there since 1999. Shell characters of M. transversum are given and compared with those of the common, closely related M. lacustre (Müller, 1774).