Hey Guys,
I just purchased some macro from Gulf Coast Ecosystems, I ended up with this little guy as well! He was in some of the macro. When I put it in the tank he popped out and dug himself into the sand bed, was kind of funny to watch as he would takes sand and rock and stack it on his back. Finally found him again after a few hours of him being MIA. I yanked him out before any damage could be done.. any clue what he might be? ... his claws are very small, I'm just not sure what to think of this guy..thanks in advance!

Look up gall crab ?

Could also be some form of decorator crab given the "stacking" behavior you mentioned.

I believe the decorator crabs are pretty reef safe. Every once in a while they may snip off a polyp or something to camouflage itself with.

Gall crabs, on the other hand could turn into a hassle. They dig "galls" or little holes in stony corals and while this doesn't necessarily hurt the coral, it's ruins the appearance. It's something you wouldn't want breeding in your tank, put it that way.

he is roughly the size of a dime... I think the Gall crabs are smaller than that....