Just realized these are worms.

i would also watch closely for eggs if there was 2 of them, don't want a breeding pair in your reef.

 

Those are some interesting nudi's. Different nudi's eat different things. Those look nothing like the species that eat zoa's and monti's. Ive never heard of one eating GSP, but apparently something keeps in check in the wild, so this isnt surprising. The eggs will be tiny white dots typically in a circle or "C" pattern and there will be anywhere from 20-200 of them in one cluster. They can also be inside the rock, and you will not be able to remove them. I suggest removing the rock totally, and inspect your tank thorughly before adding anymore GSP.

 

Thanks for the advice but that's so not gonna happen. I think it would do more harm taking all the rock out and inspecting than to just leave it in there and keep an eye to see if anymore spawn.

 

You've clearly never had a problem with nudibranchs before. They can devastate a tank if not dealt with immediately. We had montipora eating nudibranchs take out over 20 large montipora colonies in our tank before we could do anything about it.