These are Several meanings:
Opening in the eggshell that is preformed during the processes of eggshell formation in some platyhelminthic species (e.g., most Digenea, some Monogenea, Heterophyes heterophyes , Diphyllobothrium); the eggs become operculate; several related species (e.g., schistosomes, Taenia ) have nonoperculate eggs, the wall of which becomes disrupted during hatch of the larva ( Platyhelminthes/Reproductive Organs).
Cover of eggs of insects, which opens, when larva leaves the egg, e.g., lice.
Plate at the ventral side of mites to cover the sexual opening in some species.
Plate at the terminal side of the foot of snails, which may close the shell.
Portion of the human brain.
Cover of the Bryozoan brood chamber.