De zoetwatermollusken van de ‘Kijktuin’ in Oosterend, Terschelling

Summary In the wake of my study of the terrestrial molluscs present in the ‘Open garden’ of the Bos family, living in Oosterend on the Wadden island Terschelling (Mienis, 2015), a survey dealing with the presence of freshwater molluscs in the same area was carried out in the autumns of 2014 and 2015. Two aquatic habitats were present: a round pond with a varying diameter of 7-11 m, depending on rainfall in 2014 and 2015 respectively, and a partially dry ditch bordering the Open garden at all sides. Of this ditch only the part between the garden and the main road in the South carried some water. Only eight different species of freshwater molluscs were collected: four in the pond and six in the ditch. Two species were found at both sites: Gyraulus crista and Pisidium obtusale. Two species encountered in the ditch, Anisus septemgyratus (also known as A. leucostoma) and Pisidium obtusale, are indicative for temporarily drying out habitats. In the coming years I hope to have another look at the aquatic mollusc fauna of the Open garden.