I can't believe it, but maybe I need to. I have the same problem in that my "rainbow polyp rock" is all closed up. I thought there might be something chemically wrong, like I just had to use the slime control twice since I got the rock several months ago, but since you said this about the sundial snail, whoa, I noticed one that's had it's foot buried in the polyps for a while now, didn't think anything of it. How does it damage the polyps? Does it just eat the smaller ones, forcing the larger ones to stay closed up?