Operculum (in pregnancy), the cervical mucus plug that blocks the cervix of the uterus after conception
Amphibola crenata (titiko in the Māori language or mud-flat snail in English) is a species of air breathing snail with an operculum, a pulmonate gastropod mollusc which lives in a habitat that is intermediate between the land and the sea, not entirely terrestrial and not entirely marine.
Red-rimmed melania, small freshwater snail with an operculum, in the family Thiaridae