What is this white thing

[Ruple1984]

Woke up and seen this weird looking thing looks like a white brain under a mushroom coral it wasnt there yesterday does anyone know what it is? There is also a smaller one on the bottom mushroom in the pic thanks

 

[six2sevenproductions]

Cant see the pic too clearly. You said it was not there the night before? Must be a creature if its on the move. Research nudibranch.