Any of various snails found in mud; specifically (a) either of two European pond snails of the genus Lymnaea (family Lymnaeidae), the slender-shelled L. glabra and (less commonly) L. trunculata; (b) NZ a pulmonate, Amphibola crenata (family Amphibolidae), found on mudflats in New Zealand; (c) a snail of the marine family Nassariidae; (d) a tiny European spire shell, Hydrobia ulvae (family Hydrobiidae).