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• An operculum (gastropod), a single lid that (in its most complete form) closes the aperture of the shell when the animal is retracted, and thus protects the internal soft parts of the animal that are not completely covered by the shell. The operculum lies on the top rear part of the foot. When the foot is retracted, the operculum is rotated 180° and closes the shell.BOOK, Ruppert, E.E.

• An operculum (fish), a flap that covers the gills in bony fishes and chimaeras.
• The cover that rapidly opens a cnida of a cnidarian such as a jellyfish or a sea anemone. The lid may be a single hinged flap or three hinged flaps arranged like slices of pie.BOOK, Ruppert, E.E.

• In insects, the operculum is the name for one or more lids covering the tympanal cavity. A subgenital operculum is exhibited in stick insects and grasshoppers and allies (orthoptera).BOOK, Zombori, Lajos, Dictionary of Insect Morphology, Walter de Gruyter, 1999, 164, 3110148986,weblink An operculum also covers the eggs of stick insects an other insects.BOOK

See also

• Aptychus: A structure in ammonites which usually consists of two plates, and which was long thought to be a form of double operculum, but which more recently has been proposed to have been a jaw mechanism.

References