An epiphragm's a temporary structure which can be created by many species of shelled, air-breathing land snails, terrestrial pulmonate gastropod mollusks. Function The epiphragm's created to seal the aperture of the shell against desiccation. It's used when the snail's inactive. Most land snails are active when the humidity's high, such as after rains and at night, and become inactive during dry weather. The main feature of the epiphragm's to reduce water loss through the aperture during ina… (More on Epiphragm)