Definition of "operculum" []

• A lid or flap covering an aperture, such as the gill cover in some fishes or the horny shell cover in snails or other mollusks. (noun)

American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

• "The snail in the middle with the aperture of its shell sealed with an operculum is Pomatias elegans."
• "In the case of P. elegans, the foot has to come out first to move the operculum, which is attached to the foot, out of the way."
• "These latter filaments do not appear externally, and indeed a membrane, termed the operculum (Fig. 2, op), is developed from the front of each series of branchial apertures, Fig. 3."