This guy is my favorite:
Arrow Crab
How are these guys? Are they reef safe and do they play well with others ? They look like they could do some serious damage to other livestock . such as hermits, snails and shrimp
Here's what LiveAquaria has to say about them:
http://www.liveaquaria.com/product/prod_display.cfm?c=497+501+616&pcatid=616
Again, so far, I haven't seen my Arrow Crab go after anything, though yesterday it did catch itself a small pink worm of sorts (I believe it was a small bristleworm, which I thought was cool as heck!) Otherwise, it hasn't gone after anything else that I have seen. Other than the worm, the most I've seen it do is put it's claws out to try to scare a fish away. I saw a Hermit Crab lock onto the bottom lip of my Diamond Goby, which was worse than I've ever seen the Arrow Crab do.
That said, as LiveAquaria has stated, and others about all crabs, it probably has to be well fed otherwise it probably will become aggressive. And, just like fish, just because one person has great luck in a reef tank with a particular fish, that doesn't mean the next person will.
The Arrow Crab is cool enough in my opinion to take the risk if you don't have TINY fish, especially because I think that risk is pretty low. Plus, mine doesn't appear like it would be all that difficult to catch if it did need to be removed from the tank.
All that said, I'm no Arrow Crab expert...I'm just giving you my experiences over the past month...