Five species: Anisus vorticulus, Vertigo antivertigo, Unio pictorum, Anodonta anatina and Pisidium amnicum, are here recorded for the first time from the nature reserve ‘Het Heitje van Katham’, near Volendam, the Netherlands. 46 species of aquatic and terrestrial molluscs are known now from this unique peat-moor within a peat-bog area.