The operculum, meaning little lid,The operculum is attached to the upper surface of the foot and in its most complete state, it serves as a sort of trapdoor to close the aperture of the shell when the soft parts of the animal are retracted. The shape of the operculum varies greatly from one family of gastropods to another. It is fairly often circular, or more or less oval in shape. In species where the operculum fits snugly, its outline corresponds exactly to the shape of the aperture of the shell and it serves to seal the entrance of the shell. A small air-hole may remain to aid respiration.Perhaps the most essential function of the operculum in gastropods is to allow snails to resist drying out. This is very important in intertidal marine snails during low tide, and this also enables operculate freshwater and land snails to survive periods of drought and dry weather. In those marine species where the operculum completely seals the shell, it can also serve as a protection against predators when the snail body is retracted. In species of conch shells, the operculum is elongated and claw-shaped, and is used to dig into the sand to enable the conch to perform a leaping type of locomotion.
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