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OPERCULUM

Definition

(1) Plate-like cover of most prosobranchs which closes the shell entrance. (2) Plate of the stirrup in the inner ear of vertebrates. (3) A flaplike protective gill covering, present in higher fishes, but absent in the lower species, the sharks and rays. (4) A lid; the lid-like structure on the end of trematode and some cestode eggs which opens to release the larva.

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