Welp, thats an Asterina, but you've got the blue tint on to much for a camera shot, you can see other things in the tank with blue lines through them. So the Asterina looks blue to everyone.
I've seen them attach themselves to zoa's. Can't say for sure they consume them but the zoas don't do well when this happens. On the other side of the coin I have seen my blue linkia eating the asternias. Circle of life.