I was happily observing my aquarium today and I noticed a snail attached upside down to the water surface like it was a solid (matrix style) and I couldn't help but wonder if he was trying to eat the film at the surface. What do you think?
my Ramshorns seem to do that to adjust the buoyancy in their shells by changing the bubble trapped inside. They also may float up, then extend their bodies to simply increase their chances of finding something to catch on to so they can get back down again. I have never observed them actually eating any film on the water surface, though they will eat debris washed up at the tank glass waterline.