Tentacle slug ID?

[blakemc91]

Living on my GSP, managed to get it off.
Any help with ID would be appreciated. Seems like it was keeping the GSP closed.

 

[bradleym]

This is a nudibranch. They are frequently predators of corals, so it may have been eating your GSP. You should check for more of them also, just in case it reproduced.

 

[blakemc91]

Thank you, was afraid of that. Looks like it's flashlight time tonight.