Peringia ulvae, commonly known as the Laver spire shell or mudsnail, is a European species of very small aquatic snail with gills and an operculum, a gastropod mollusk in the family Hydrobiidae.

[2] 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.

[3] Peringia ulvae is a widespread and abundant member of the benthic fauna of estuarine habitats and coastal brackish and salt waters.

[3] Peringia ulvae seems to prefer more exposed localities with less vegetation than the mudsnails Ecrobia ventrosa and Hydrobia neglecta.

[7] On the west coast of Wales this species has peaks of spawning activity in spring and autumn and produces planktotrophic larvae (veliger)[8] that remain in the plankton for up to four weeks before settlement.

[7] The species provides an interesting case for molecular analysis as the pelagic dispersal phase raises fascinating questions on gene flow, differentiation, recruitment, and inbreeding, but there remains the potential for self-recruitment of estuarine populations.