OPERCULUM
operculum
(noun) a hard flap serving as a cover for (a) the gill slits in fishes or (b) the opening of the shell in certain gastropods when the body is retracted
Source: WordNet® 3.1
Etymology
Noun
operculum (plural opercula)
(zoology) A covering flap in animals, such as a gill cover.
(botany) The lidlike portion of a moss sporangium or of a fruit that detaches to allow the dispersal of spores or seeds.
(dentistry) A gum flap covering (part of) a partially erupted tooth, usually a wisdom tooth.
A structure which serves as a cover or lid.
Source: Wiktionary
O*per"cu*lum, n.; pl. L. Opercula, E. Operculums. Etym: [L., a cover
or lid, fr. operire to cover.]
1. (Bot.)
(a) The lid of a pitcherform leaf.
(b) The lid of the urnlike capsule of mosses.
2. (Anat.)
(a) Any lidlike or operculiform process or part; as, the opercula of
a dental follicle.
(b) The fold of integument, usually supported by bony plates, which
protects the gills of most fishes and some amphibians; the gill
cover; the gill lid.
(c) The principal opercular bone in the upper and posterior part of
the gill cover.
3. (Zoöl.)
(a) The lid closing the aperture of various species of shells, as the
common whelk. See Illust. of Gastropoda.
(b) Any lid-shaped structure closing the aperture of a tube or shell.
Source: Webster’s Unabridged Dictionary 1913 Edition