What is operculum made of?

Operculum:

1. Some plant species, mosses, and fungi have a cap-like structure known as the operculum.
2. It's a cover or lid that is typically found in plants.
3. The operculum is made up of a thin to broad corneous protein material that is exceedingly transparent and varies in color from yellow to brownish.
4. If the operculum is wet then, it is flexible; but, once dry, it becomes hard.
5. The fundamental function of the operculum is to prevent the live gastropod from drying out.