In many species, the epiphragm is a simple membrane composed of dried mucus, but in a few others such as "Helix pomatia", it is a sturdy flat calcareous structure, in which there is a small perforation, to allow for oxygen exchange.
In many species, the epiphragm is a simple membrane composed of layers of dried mucus. In a few species such as "Helix pomatia" which hibernate for many months, before hibernation each snail creates a sturdy flat calcareous structure, in which there is a small perforation, to allow for oxygen exchange.