Starfish id needed

[Jessica mauro]

So bought a live rock for tank. Apparently had quite a few hitchhikers, saw a few, one that looked like a sea biscuit, but it moved so can't photo for id, since can't find it. Can you tell me what kind of starfish this is and if it needs to be removed.

 

[Scotty Buttons]

Asterina star fish, some of them are known to eat corals.