I fragged the whole dang thing. I don't know what a limpet is but I'd sure love to so I can search my tank for them. I've had a coupe of other frags that seemed perfectly healthy do this all of the sudden and I really don't think there is anything wrong with my tank because the other corals are flourishing and growing well. It'll be a while before these frags are big enough but I fragged it almost two days ago and the frags seem to be doing fine so hopefully they'll all make it. Any more information on what this could be would be great. I'd hate to have to frag another great coral in the future because of something I can't pinpoint.