I have a bunch of pictures of copperbands on my reef along with all kinds of polyps. It still blows my mind at how wrong the "experts" are in the literature. But, they do eat a couple of things that some people like, naturally. I don't really mind if they kill an astrea snail now and then. I'll trade an astrea for an aiptasia any time. And feather dusters, well they just have to be hidden or blocked by some coral orsomething, if I want them in a large reef. My next experiment with them it to see if I can keep a clam in there with them. I have seen it done in a picture. I'll let you know. They don't bother the spondylactiis oysters at all and those are exposed enough at feeding time for a serious bite if it was something they were prone to trying. Hasn't happened at all with mine. I must stress that these are the Indonesian Copperbands.
Manny, if I just had one in a snail shell and thats all it amounted to, I would take the shell out and do something with it until I knew. Lots of things start out small with little polyps that are not aiptasia.
Be forewarned though, it is a trick to get a copperband healthy and converted to frozen foods. You gotta really be dedicated to it. And I wouldn't try to keep more than one, unless you keep a group of them all put in the tank at the same time. The age we get them at usually is pre-puberty and they are serious about being lone rogues at that age. Two of them are likely to fight to the death. This might not hold true in a 500 gallon or larger tank, but how many people have those sitting around?