Two different types of snail shell discovered today in the Thames. The top one is a Nerite Snail (Theodoxus fluviatilis), the bottom one is a Laver Spire Shell (Hydrobia ulvae). Both can tolerate the brackish conditions of the tidal Thames, and the nerites are very numerous. Nerites graze on algae and are often kept in aquariums to help keep the tank clean. Their shells can be a range of colours and patterns, so they are also attractive to have on display.