Lister's river snail

Lister's river snail: While diving in Lake Zug sometimes one sees Lister's river snail (Viviparus contectus). — Nikon D200, Nikkor AF Micro 60mm, Lake Zug, Restaurant Baumgarten, 19 May 2013. Nikon D200, 1/250 s, F/22.0, 60 mm, ISO 200, Sunday, May 19, 2013 11:24:22