looks like a serpent star ..somewhat tank safe.. they can be opportunistic feeders such as feeding on small fish that hide in rock work would not be a bad idea to spot feed him periodically,, meaty foods.. if you all of the sudden start losing small fish hes your likely culprate.
I found one very simular to that. It was serphant stare. It was just a little darker then yours but fish get lighter and darker anyway depending on their conditions.