Freshwater snails

At all taxonomic levels, gastropods are second only to the insects in terms of their diversity.
Gastropods have the greatest numbers of named mollusc species. However, estimates of the total number of gastropod species varies widely, depending on cited sources. The number of gastropod species can be ascertained from estimates of the number of described species of Mollusca with accepted names: about 85,000 (minimum 50,000, maximum 120,000). But an estimate of the total number of Mollusca, including undescribed species, is about 240,000 species. The estimate of 85,000 molluscs includes 24,000 described species of terrestrial gastropods. (information from Wikipedia)