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-4 in the Appendix of Indo-European roots.]
o·percu·lar (-lər) adj.
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2018 by Houghton Mifflin Harcourt Publishing Company. All rights reserved.