Thank you for your reply. I have nothing that resembles the nudi in my tank. I have read that they take on the colour of what they eat, so wondered if this is just a young one that hasn't yet demolished my zoas!
No problem. Not sure where that post came from... I'll manage it, but keep on the nudibranch. If there is something in there that they do want to consume there is a chance that there are eggs already in it. You remove the adult and you will find another.