De Rivierparelmossel Margaritifera auricularia (Spengler, 1793) van Katwijk

A valve of Spengler’s Freshwater Mussel Margaritifera auricularia was found on the beach of Katwijk. This beach is known as a place where fossil Holocene freshwater bivalves are often washed ashore. Until now many Unio crassus, and less common U. tumidus and U. pictorum were found. Anodonta shells are rare. The reason is that in earlier times (Holocene) the River Rhine debouched into the North Sea at this locality. Disturbance of the bottom by wave action causes the shells to be washed ashore. Described here is the second record of Margaritifera auricularia in the Netherlands.