Epiphragm:
An epiphragm (from the Ancient Greek ἐπί, epi ” upon, on, over ” and φράγμα, -phrágma “fence”) is a temporary structure which can be created by many species of shelled, air-breathing land snails, terrestrial pulmonate gastropod mollusks. It can also be created by freshwater snails when temporary pools dry up.
In most species, the epiphragm is made of dried mucus, and although it is elastic, it is fairly easily torn when forcibly removing a snail from its substrate. In a few species, the epiphragm is thick and quite rigid, being reinforced with calcium carbonate. This kind of epiphragm is very strong and may be difficult to break. [Wikipedia]
Survival strategies. Noted in this Animalogic video, The 13 Animals With The Most Extreme Sleep Behaviours:
