I am new to the reef keeping hobby and recently introduced some of my first coral to the tank (two zoa frags). I did dip the corals so I was fairly confident that I would not be introducing anything bad in the tank. Unfortunately, today I noticed that one of the zoanthid polyps has remained closed for some time. On closer inspection, I noticed a small brown spikey thing on it which appeared to move as I continued to monitor it. I was able to take a picture using my camera with a macro lens and based on others I have seen on the internet I am quite confident that it is some form of nudibranch. Can anyone confirm this for me and let me know whether it is worth trying to eradicate it from the coral or if I should just discard the whole frag (was only $10). Thanks