looking for an ID

[Snappy]

Anyone know what this thing is? I discovered it the other night after lights out. Sorry for the poor photos, they were taken using a video camera & flashlight. Anyway the (nudibranch?) looks all black except for a thin white stripe in the middle of its back and is about the size of a loonie. Shown here with the glass reflection creating a mirror image so you can see its top and underside. I am also assuming it's reef safe as I have no idea how long it's been in my tank or where is originated from.