Anisus vorticulus – a rare and threatened water snail

The ram's-horn snail Anisus vorticulus is one of the rarer and more geographucally restricted freshwater mollusc species in Britain. In this region, A. vorticulus is largely confined to 'traditional' grazing marshes, where it lives in ditches with clean, often calcareous, water with a rich aquatic flora. It has always been a very local species in Britain (Fig. 1), being