Hi, saw your threat and thought I'd help out. This is not a berghia nudi. It is probably a coral eater or sponge eater. What have you added to your tank in the last week or so? That should give you a clue. Also, many nudis take on the color of the thing they eat. See if you can spot some on your rock and look at their color. This might help too.
It would be a very rare thing for a berghia to as a hitch hiker.