Lymnaea (Snail)

 Lymnaea stagnalis Linneus (L.) (Pulmonata, Basomatophora) is a widely distributed inhabitant of freshwater ponds, lakes and rivers rich in vegetation and is found throughout Europe, the Northern United States and parts of Asia. The snails are from 2 to 5 cm in shell length and typically are found in large numbers close to the water surface (Fig. 1) feeding on floating pond weed. They also feed on algae, detritus and carrion and so are generalists in their feeding habits. Lymnaea has a gas-filled lung and ventilation is accomplished by opening and closing movements of the apex of a muscular tube (the pneumostome) that forms the entrance to the lung (Fig. 1). Skin respiration is also important in Lymnaea and its relative importance compared to lung ventilation depends on the oxygen content of water. Locomotion is carried out by the coordinated front-to-back beating of cilia on the sole of the foot but recent studies have revised the ciliary model of locomotion to include a major role for peristaltic waves of smooth muscle contractions. If food is placed beneath the water surface, say at the bottom of an aquarium tank, then the snails carry out regular cycles of locomotion to and from the water surface to alternate feeding with breathing.

The reproductive biology of Lymnaea has been well-studied. It is a simultaneous hermaphrodite but during mating behavior one individual acts as the male and the other the female. Often this is immediately followed by a reversal of sexual roles by the same pair of snails. During oviposition, gelatinous egg masses, each containing 100 eggs or more, are deposited on the substrate and tiny snails in adult form eventually emerge without any free-living veliger larval stage. This makes it simple to breed snails in the laboratory, a major advantage for behavioral and molecular studies where large numbers of animals are required.