When I got my last batch of LR
there were a gazillion crabs and thus far I have identified spider crabs, emerald crabs, weird furry crabs, crabs that look like porcelain crabs, and some crabs that I still have not IDed yet, some of them are fast and orange like you mentioned.
Some are described as not entirely reef safe but I'm letting them hang out for the moment.
If you decide you want that crab out of there, I have used a mason jar tipped at 45 degree angle leaning up against the LR
that the crab hangs out in, with a piece of meat at the bottom (shrimp or what have you) the crab slides on down and can't seem to crawl back out. Put the jar in at night and retrieve the next morning. Remove the 20 hermit crabs that fell in the glass first.
I used this because I was trying to get the crab that was harassing my serpent star but instead all I got was lots of smaller crabs, the big wily one never went in apparently. I ended up just leaving him in there.
If anyone is going to have crab troubles it might be me, because I am hosting crab central right now. But the only thing my crab army has done thus far has been harassing my serpent star occasionally. I just keep them all fed. I imagine that eventually some of my crabs will get to big and too crabby and will have to go.
Wetwebmedia has lots of crab id. Here are 3 links I have found helpful. Maybe your crab is in there.
Hope this helps... I hope your crab is a friendly one.. they are fun to watch.
edited: Here is another really good link I forgot.