Normally the only nudi's i know of that are reef safe are the Berghia and Blue Velvet nudibranch. Im kinda on the fence about these little guys cause a good friend of mine purchased a few online that are suppose to be reef safe and they ended up snacking on his sea fans, softy corals, etc.... wasnt a good ordeal. Berghia are the only ones id feel comfortable with, but your does look awful close to a berghia so its hard to tell.