So, I have a minor mystery on my hands. I just pulled out a pond snail shell from my tank that was completely empty. It's pretty translucent and I can see that there's nothing in it. Any ideas as to what happened to the guy? He lived in a tank that has a small school of gold pristella tetra (who tend to ignore the snails), two emerald catfish and a ghost shrimp. There are about 8 or so other pond snails in the tank who appear healthy.