Gyraulus laevis (Mollusca: Planorbidae) in Nederland

All distribution data of the planorbid Gyraulus laevis (Alder) in the Netherlands have been collated (see fig. 1). It appears that in most cases the species had established itself only temporarily and it is almost always locally uncommon. In the dunes along the seashore the situation is remarkable in this respect that G. laevis is now known to occur only in various lakes and pools at Wassenaar near The Hague. These waters belong to the systems of the municipal waterworks of The Hague and are formed by artificial infiltration of water from the river Lek. Attention is drawn to a possible preference for waters with comparatively high nitrogen content. It is likely that to a certain extent G. laevis relies on birds for its dispersal.