Berghia Nudibranch ??

could also be a zoa eating nudibranch.

i was thinking zoa eater also.

deff looks like zoa eating to me get rid of it!

Did you buy it or is it a hitch hiker?

you should email to one of the websites selling berghia nudibranches for id. Would be a great hitchhiker if it was.

I agree that it's a zoanthid eating nudibranch. I just had an infestation of these things in my tank so I have become quite familiar with their appearance. I have noticed that Berghias have more cerata on its back which give it a hairy look to it. I would look for eggs if I were you.