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Pond Snails (Lymnaeidae)

Pond snail (Lymnaea stagnalis). [RN]

Pond snails (Lymnaeidae) are a snail family abundant in our lakes and ponds. They also happen to live in many garden ponds, as well as in aquarium tanks, where they were either introduced sitting on water plants, or placed intentionally.

A pond snail can have a shell as long as 7 cm. That makes pond snails considerably larger than, for example, the Roman snail (Helix pomatia), the largest terrestrial snail in Central Europe.

Like frogs, pond snails are able to meet their oxygen requirement by cutaneous respiration directly through their skin. Albeit their living in the water, pond snails are lung breathers, they have to surface to breathe fresh air. Then, on a slime thread, they can also crawl backside down on the lower side of the water surface.

Pond snail (Lymnaea stagnalis) [RN]

Systematically pond snails are placed among the water lung snails, the Basommatophora. Those are to be distinguished from the land lung snails (Stylommatophora) by having only two tentacles instead of four, which besides are widened to an ear-like shape. A pond snail's eyes sit at the tentacle's base, hence the systematic name Basommatophora (base-eye snails).

Like the Roman snail, pond snails also are hermaphrodites, being male as well as female. In contrary to the stylommatophoran Roman snail, pond snails have two genital openings, a male one and a female one. That makes a simultaneous Helix-style mating procedure impossible: Mating takes only place in one direction at a time. Pond snails' characteristic egg-packets are placed on water plants and stones.

In populations with a low number of individuals, for example after a pond snail species freshly settling in a new pond, pond snails are also capable of auto-fertilization. As this, of course that only increases a population's head-count, in order to recombine genes, pond snails still have to rely on common sexual reproduction.

Pond snails have also been used as a research object in the field of genetics. Using the example of the common pond snail (Radix labiata, at that time Lymnaea peregra), the American geneticist Alfred Henry Sturtevant (1891-1970) was able to prove, how a snail shell's coiling direction is inherited.

On a slime thread, pond snails also can crawl on the water surface's underside. They do so to feed or simply to move from one place to another.

A pond snail (Lymnaea stagnalis) crawling on the water surface's underside. [RN]

     

Pond snails common in Europe:

An oval pond snail (Radix balthica) camouflaged with water plants. [RN]

Stagnant or Great pond snail (Lymnaea stagnalis):
Shell height 4,5 - 6 cm, giant forms even up to 7 cm, in dependence of the environment in littoral areas also much smaller forms. Occurrence in slow-moving and stagnant waters rich in plant growth, in all of Europe except the islands of the Southern Mediterranean.

Common pond snail (Radix labiata):
Long oval form with straight sidelines. Shell spire conically erect. Relatively hard shell, between darkly horn coloured and brown, mostly with a brown-black coating. Stagnant and slow moving waters, often small water bodies deficient in lime. More resistant against drying out of its home pond than other Radix species. All of Europe including the Far North and Western Asia.

Ear-shaped pond snail (Radix auricularia):
Last whorl elate and ear-shaped. Shell height up to 35 mm. Lives in lakes rich in plant life, backwaters and calm river bays in Europe including the Mediterranean (except Sicily and the Peloponnesus), West and North Asia.

Oval pond snail (Radix balthica):
Much smaller than the ear-shaped pond snail, whorls more bulbous, body whorl less elate. Lives in lime-rich waters (creeks, rivers and lakes) in all of Europe, except Southern Spain and the Peloponnesus.

Lesser pond snail (Galba truncatula):
Very small snail, with whorls set off like stairs. Usually about 6 to 8 mm in length, though there are also smaller dwarf specimens, as well as giant forms, between 3 and 15 mm. The lesser pond snail is the intermediate host of the liver fluke (Fasciola hepatica).

Complete species list for the United Kingdom and Ireland:
According to Clecom (January 2008)

Lymnaeidae Rafinesque, 1815

Lymnaeinae Rafinesque, 1815

Galba Schrank, 1803

Galba truncatula (O.F. Müller, 1774)

Stagnicola Jeffreys, 1830

Stagnicola palustris (O.F. Müller, 1774) *)
Stagnicola fuscus (C. Pfeiffer, 1821) *)
Stagnicola corvus (Gmelin, 1791)

Omphiscola Rafinesque, 1819

Omphiscola glabra (O.F. Müller, 1774)

Radix Montfort, 1810

Radix auricularia auricularia (Linnaeus, 1758)
Radix labiata (Rossmässler, 1835) **)
Radix balthica (Linnaeus, 1758)

Myxas G.B. Sowerby I, 1822

Myxas glutinosa (O.F. Müller, 1774)

Lymnaea Lamarck, 1799

Lymnaea stagnalis (Linnaeus, 1758)

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*) Ireland only.
**) United Kingdom only.