Peringia ulvae, also known as Peringia ulvae, common name the Laver spire shell or mudsnail, is an European species of very small aquatic snail with gills and an operculum, a gastropod mollusk in the family Hydrobiidae.This is arguably a marine snail, but it is often also listed as a non-marine species because it tolerates brackish water and lives in salt marshes and similar habitats.When it is within the genus Peringia, this species is the type species of the genus Peringia.