A clear snail?

So the other day I saw this snail while walking. What first caught my eye was the colours on the shell. Then I saw that the bit sticking out looked clear. Maybe this i common among snails, or something that happens while they sleep, for example maybe hide their body and excrete some sticky clear stuff... I suppose I should wikipedia or google this.

Not sure but it looks like at least on this website they also got pictures of snails that have clear parts on their bodies.... I'll have to do more research.