What type of corals do you have? Notice anything missing? If it’s a berghia, maybe a score? But if it turns to be an unwanted guest, that little bugger might not be the one to worry but a mass of eggs
This looks like my Monti eating nudibranchs too, I will look for a better photo and send it. It is worth dipping some montis just to see if more fall off to help confirm
So I was cruising through the garage the other night and decided I would peak at the frag tank in the garage since its been getting so cold at night I have been worrying about the temperature dropping too much and I found what I am 99.99% certain are montipora eating nudibranchs, while not great...
If your montis are removable you can QT and begin a dip regimen to prevent them from propagating and eating all your montis. Maybe save all your montis before they’re dead.
I ended up just tossing all my montis and going montiless for about 3-4 months, I put some testers in maybe a month ago and they have been doing fine so far. Depends of course how many montis you have and how attached you are to them. My reasoning was the sooner I pull out their food source the sooner they would starve to death