Regarding the vermetid Snail, my tank has literally been taken over by them. I am absolutely convinced that by smashing them it causing them to spread more because thats how it seemed for me. I started off with a few, crushed them, and then the following week had double. I absolutely hate these guys.. They are literally growing on everything from rock, to the glass, powerheads, frag racks, on all my zoa plugs, and even my darn snail and hermit crab shells. What is the big deal with these vermetid snails anyway? Do they do any harm to anything? I have so many in my tank that when i finish my next tank build I will probably not transfer ANY coral or anything else over to that tank in fear i might introduce them.
I would suspect that there is absolutely no known natural predator for these guys because they have a crazy hard shell.