Operculum (animal)

An operculum (animal) is an anatomical feature, a stiff structure resembling a lid or a small door that opens and closes, and thus controls contact between the outside world and an internal part of an animal. Examples include:

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.

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