1. Potamopyrgus antipodarum. Darker dorsal surface of tentacle and fine white medial line indicated by arrow. Ribbing inside aperture is ctenidium (gill). From slowly flowing freshwater pool at top of salting, Dee Estuary, Cheshire
2. Potamopyrgus antipodarum. Darker dorsal surface of tentacle and fine white medial line indicated by arrow. Ribbing inside aperture is ctenidium (gill). From slowly flowing freshwater pool at top of salting, Dee Estuary, Cheshire

Potamopyrgus antipodarum. Darker dorsal surface of tentacle and fine white medial line indicated by arrow. Ribbing inside aperture is ctenidium (gill). From slowly flowing freshwater pool at top of salting, Dee Estuary, Cheshire