Freshwater snails are gastropodmollusks that live in fresh water. 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. In addition, some are amphibious and have both gills and a lung (e.g. Ampullariidae). Most feed on algae, but many are detritivores 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
The following cladogram is an overview of the main clades of gastropods based on the taxonomy of Bouchet & Rocroi (2005), modified after Jörger et al. (2010) and simplified with families that contain freshwater species marked in boldface: (Marine gastropods (Siphonarioidea, Sacoglossa, Amphiboloidea, Pyramidelloidea) are not depicted within Panpulmonata for simplification. Some of these 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
The Caenogastropoda are a large group of gilled operculate snails, which are largely marine. In freshwater habitats there are ten major families of caenogastropods, as well as several other families of lesser importance:
Ampullariidae, an exclusively freshwater family that is largely tropical and includes the large "apple snails" kept in aquaria. 105–170 species.
Viviparidae, medium to large snails, live-bearing, commonly referred to as "mystery snails". Worldwide except South America, and everywhere confined to fresh waters. 125–150 species.
Basommatophorans are pulmonate or air-breathing aquatic snails, characterized by having their eyes located at the base of their tentacles, rather than at the tips, as in the true land snails Stylommatophora. The majority of basommatophorans have shells that are thin, translucent, and relatively colorless, and all five freshwater basommatophoran families lack an operculum.
Chilinidae, small to medium-sized snails confined to temperate and cold South America. About 15 species.
Latiidae, small limpet-like snails confined to New Zealand. One or three species.
The freshwater snail Physa acuta is in the subclass Heterobranchia and the family Physidae. P. acuta is a self-fertile snail that can undergo either sexual reproduction or self-fertilization. Noel et al. experimentally tested whether accumulation of deleterious mutations is avoided either by inbreeding populations of the snail (undergoing self-fertilization), or in outbreeding populations undergoing sexual reproduction. Inbreeding promotes the homozygous expression of deleterious recessive mutations in progeny that then exposes these mutations to selective elimination because of their deleterious affects on progeny. Outbreeding sexual reproduction allows females to choose male mating partners with smaller mutation loads that then also leads to a reduction of deleterious mutations in progeny. On the basis of their findings, Noel et al. concluded that both outbred and inbred populations of P. acuta can efficiently eliminate deleterious mutations.
As human food
Several different freshwater snail species are eaten in Asian cuisine.
^Dillon R. T. (2006). Chapter 21. Freshwater Gastropoda. pages 251–259. In: Sturm C. F., Pearce T. A. & Valdés A. (eds.) (2006). The Mollusks: A Guide to Their Study, Collection, and Preservation. American Malacological Society, 445 pp. ISBN978-1-58112-930-4.
^Jörger K. M., Stöger I., Kano Y., Fukuda H., Knebelsberger T. & Schrödl M. (2010). "On the origin of Acochlidia and other enigmatic euthyneuran gastropods, with implications for the systematics of Heterobranchia". BMC Evolutionary Biology10: 323. doi:10.1186/1471-2148-10-323.
^ abcdefghijklmnBanarescu P. (1990). Zoogeography of Fresh Waters, Vol. 1, General Distribution and Dispersal of Freshwater Animals. AULA - Verlag, Weisbaden.
^ abNoël E, Fruitet E, Lelaurin D, Bonel N, Ségard A, Sarda V, Jarne P, David P. Sexual selection and inbreeding: Two efficient ways to limit the accumulation of deleterious mutations. Evol Lett. 2018 Dec 10;3(1):80-92. doi: 10.1002/evl3.93. PMID: 30788144; PMCID: PMC6369961
Haynes A. (2000). "The distribution of freshwater gastropods on four Vanuatu islands: Espiritu Santo, Pentecost, Éfate and Tanna (South Pacific)". Annales de Limnologie36(2): 101–111. doi:10.1051/limn/2000006, PDF.