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n. pl. o·per·cu·la (-lə) or o·per·cu·lums
Biology A lidlike structure covering an opening, especially:
a. A bony plate that covers and protects the gills of most bony fishes. Also called gill cover.
b. A horny or calcareous plate attached to the foot of most larval and many adult gastropods, used to close the aperture when the animal retracts into its shell.
c. A covering at the top of the spore capsule of most mosses, falling off when mature spores are released.

[Latin, lid, from operīre, to cover; see wer- in Indo-European roots.]

o·per′cu·lar (-lər) adj.
American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
References in periodicals archive ?
Although certainly present, opercula are not known in Asgardospira, Lytospira or Lesueurilla (or in most fossil gastropods) but several euomphalines have a prominent calcified operculum (Yochelson & Linsley 1972; Yochelson 1979; Peel 2015).
The fruits have one to several locules, each with a single seed, with or without specialized structures for germination, such as stopper-like opercula or valves that hinge open.
A second structure that can be used to determine the age of gastropods is the operculum (plural opercula): a shield-like plate, often wholly organic, that the gastropod uses to close off its aperture and protect the soft body tissues inside the shell from predatory attacks and in intertidal species to prevent potential desiccation.
Neurogenesis suggests independent evolution of opercula in serpulid polychaetes.
Three eggs had their opercula detached and shells destroyed to allow examination and measurement of the operculum and internal micropylar plate.
Abstract--Aging of tautog (Tautoga onitis) has historically required sacrificing fish to obtain opercula and otoliths.
The combination group showed significant increases in metabolism in a number of regions, including the right hemisphere cluster (insula/putamen/ amygdala/superior and middle temporal region); the left middle temporal pole fusiform gyrus and anterior temporal region; the right middle and inferior frontal region; and the right rolandic opercula.
The opercula in both sexes bear small and irregularly arranged spots (Esmaeili et al.
We observed gill lice on gills (n = 34; 46.0% of all those observed), branchial rims (n = 22; 29.7% of all those observed), opercula (n = 17; 23.0% of all those observed), and at the base of one pectoral fin (n = 1; <1% of all those observed) of kokanee salmon.