Funny, I saw these for the first time about a month ago while at a fish convention. I was amazed and had no idea what they were at the time. Nothing like I'd ever seen. They are evidently coming in on acans/micromussa (or whatever... I don't claim to know much about corals
and the corals I saw were riddled with them. Man, I totally forget their name, but it's home in my notes (I'm at work).
They are a crab or a shrimp... something like that, if I remember correctly.... they look more like a crab but I remember thinking I would never have guessed them as such.... so I'm not sure.
They are harmless to your coral, I remember that.... I think. I got a few really really bad pictures at home as well. They were in one of the zero-edge tanks and there is no way to focus with those unless you have a photobox.... mine wasn't with me.
I will get you the name when I get off
I want one.... LOL.