The Littorinidae are a taxonomic family of over 200 species of sea snails, marine gastropod molluscs in the clade Littorinimorpha, commonly known as periwinkles and found worldwide. In English-speaking countries, gastropod molluscs from other families, such as the Neritidae, are sometimes also commonly known as “winkles” because they are small, round snails that occupy a similar ecological niche.