Nerita is a genus of medium-sized to small sea snails with a gill and an operculum, marine gastropod molluscs in the subfamily Neritinae of the family Neritidae, the nerites.

The operculum is a corneous or calcareous anatomical structure like a trapdoor that exists in many groups of sea snails and freshwater snails, and also in a few groups of land snails; the structure is found in some marine and freshwater gastropods, and in a minority of terrestrial gastropods, including the families Helicinidae, Cyclophoridae, Aciculidae, Maizaniidae, Pomatiidae, etc.