Het voorkomen van Basters drijfslak Heleobia stagnorum (Gmelin, 1791) op Zuid-Beveland

Jaap Woets and the author have constituted ‘Basters equipe’ to inventories Heleobia stagnorum in the Dutch province of Zeeland. In 2011 on Zuid-Beveland H. stagnorum was encountered in brackish water in 12 places. The species was always accompanied by Ecrobia ventrosa and in two-third of the places by Potamopyrgus antipodarum. It remains to be investigated why H. stagnorum is absent from some seemingly suitable brackish waters.