Ampullariidae (apple snails) is a family of freshwater snails. Members of this family are the largest extant freshwater snails.
When searching for gastropods in tropical collection conservatories of Flora Olomouc I have found also these four large shells of apple snails. They are used as hanging flower pots for tropical plants.
Ghesquiere S. 2012: http://www.applesnail.net/ accessed 25 May 2012