a. the hard bony flap covering the gill slits in fishes
b. the bony plate in certain gastropods covering the opening of the shell when the body is withdrawn
2. Botany the covering of the spore-bearing capsule of a moss
3. Biology any other covering or lid in various organisms
Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.
the fold of skin that covers the outside of the gill slits in the majority offish (except the shark and ray) and in the larvae of amphibians, especially tadpoles. The operculum of fish of the class Osteichthyes has bones. In the majority offish the operculum plays an active role in breathing: when it is lifted, a vacuum is created in the gill cavity, and water passes from the mouth and pharyngeal cavities into the gill cavity by way of the gill apparatus. It is possible to determine the age of some fish according to the annual rings on the operculum bones.
The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.
The soft tissue partially covering the crown of an erupting tooth.
That part of the cerebrum which borders the lateral fissure.
A lid, flap, or valve.
A lidlike body process.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.