Hmm... My eyes might be deceiving me, but as I watch the video it almost looks like it has a forked tail which would lead me to believe it's a flatworm of some sort. Whether it's the dreaded AEFW I'm not sure. If the coral is dead though and the creature is still on it, just give the skeleton a quick freshwater dip in a tupperware container and it should fall right off. After that try and get some close up shots of it. GL.