Many retailers, both LFS' and online, often sell several species of shrimp labeled "peppermint", some will eat the aptasia, and some will not. One almost definate method of ridding the tank of them is to injest the anemones with a very strong kalkwasser solution using a hypodermic needle. Not only does the puncture cause it stress, but the kalk saolution will dissolve what is left, and you get the added benefit of a little better calcium level in your tank. lol