The first image that usually comes to mind when we talk about snails is the sluggish animal that has a brown shell which can easily be noticed along the walkway. Something like what you see on the left.
However, this isn’t the case for all snails! Some species of snails, like The Napaeus barquini, are able to 
slurp up crusty lichen and apply them with their mouths to paint mounds of the mucky cover-up onto their shells. They are able to deposit lichen material even in the farthest regions of its shell by extending their bodies amazingly far beyond the shell margin, till they look they like this.
Disgusting, I know. However, due to this camouflage layer the outlines of the shell merge optically with the surface of the rock faces, presumably an adaptation to natural enemies such as birds and lizards. This ability to adjust and adapt is very similar to those animals which was mentioned in lecture, like the difference in lycaenid butterflies living at different altitudes.
Never knew that snails could come up with such ingenious ideas, did you?
References:
"Snails As Clever Builders: Active Camouflage In A Snail". Science Daily, 31 Oct 2007.
"Snails Fashion Their Own Camouflage", by Jeanna Bryner. LiveScience, 31 Oct 2007.