Een klep van Unio tumidus Philipsson, 1788 op Texels strand

How could a nearly perfect valve of the freshwater mussel Unio tumidus reach the North Sea beach of the island of Texel? This species does not occur in the freshwater habitats on the island. Those found infrequently on the beaches of the mainland of the Netherlands are usually worn and partly fossil. Our specimen is certainly recent. Birds are unlikely transporters of a single valve over a large distance. Souvenir shops on Texel are the most probable source. We observed freshwater mussels, both with and without intact periostracum, in shops on Texel.