Two exerpts from Wetwebmedia,
"Just an FYI to all of you getting lured into buying 'reef safe' peppermint shrimp. Be cautious. So far $3 peppermint shrimp wiped out 2 of my plate corals. Now that they are gone, I can't wait to see what they move onto next.
>>Wow, gotcha. This is the biggest problem we have with common names. I bet you *didn't* get Lysmata wurdemanni, which is the animal that we all love and often use to control Aiptasia. However, there is at least one other animal that goes by the "Peppermint" moniker, Rhynchocinetes spp., with large eyes and a beaklike "nose" (you'll also note that their color saturation is strikingly different and much stronger)."
and here's another one from Anthony Calfo,
"<reef shrimps of the genus Lysmata have a long-standing and well-documented history of nipping, eating or harassing desirable reef invertebrates (corals and clams are favorite foods at times <G>). The peppermint shrimp has become popular recently as you have discovered for eating Aiptasia. The addition and practice is ill-advised in my opinion. We cannot expect these shrimp to eat one cnidarian (the Aiptasia) while leaving other cnidarians (corals like your Xeniid) alone. It just doesn't work that way."
HTH