The Probert Encyclopaedia of Nature

OPERCULUM

In zoology, an operculum is a lid or flap of skin covering an aperture, such as the gill slit cover of fish and larval amphibians and the horny calcareous operculum secreted by many gastropod molluscs, which closes the opening of the shell when the animal is inside. In botany an operculum is the cone-shaped lid of the capsule of mosses, which is forcibly detached to release the spores.
Research Operculum