Freshwater gastropod
Freshwater snails are gastropod mollusks which live in freshwater. There are many different families. They are found throughout the world in various habitats, ranging from ephemeral pools to the largest lakes, and from small seeps and springs to major rivers. The great majority of freshwater gastropods have a shell, with very few exceptions. Some groups of snails that live in freshwater respire using gills, whereas other groups need to reach the surface to breathe air. Most feed on algae, but many are detritivors and some are filter feeders.
According to a 2008 review of the taxonomy, there are about 4,000 species of freshwater gastropods (3,795-3,972).
At least 33–38 independent lineages of gastropods have successfully colonized freshwater environments. It is not possible to quantify the exact number of these lineages yet, because they have yet to be clarified within the Cerithioidea. From six to eight of these independent lineages occur in North America.
The following cladogram is an overview of the main clades of gastropods based on the taxonomy of Bouchet & Rocroi (2005), with families that contain freshwater species marked in boldface: (Some of the highlighted families consist entirely of freshwater species, but some of them also contain, or even mainly consist of, marine species.)
† Paleozoic molluscs of uncertain systematic position
† Basal taxa that are certainly Gastropoda
† Paleozoic Neritimorpha of uncertain systematic position
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