Young specimens have a coarsely tomentose epiphragm (membranous cover) that soon disappears. The operculum serves some of the same functions as an epiphragm. A white convex epiphragm is created for aestivation. This kind of epiphragm is a solid structure composed mainly of calcium carbonate. This kind of epiphragm is very strong and may be difficult to break. A mucus epiphragm is usually transparent or translucent, and is fairly elastic. The epiphragm is created to seal the aperture of the shell against desiccation. The important feature in reducing water loss in land snails during inactivity is an epiphragm.