Epiphragm

A Epiphragma (Greek ἐπιφράγμα, lid ') is a Kalkverschluss of snail shells, which protects the soft body of the snail from dehydration and freezing. The Epiphragma is but air-permeable, so that the worm can continue to breathe. Snails form a Epiphragma when they move to their winter hiding place.

A Epiphragma is in contrast to an operculum or a clausilium a rigid closure, which is formed when necessary by means of a body's secretion. The screw discards the shutter when it is no longer needed.