Crab Identification

Hi all, I'm italian and this is my first post on this ng.
I'm trying to identify a crab that I've discovered in my small reef
tank (4g):
http://www.flickr.com/photos/big_cory/267291286/
http://www.flickr.com/photos/big_cory/267289474/
At the moment it seems to be quiet and it doesn't annoy corals and fish
(at the moment I've only xenia and zoanthids and a yellowtail damsel
fish). I often saw it eating on the sand and on the live rocks, so I
suppose, but I'm not really sure, that it could be "vegetarian".
His sizes are about 2/2.5 cm (0.8 inches) but his pincers are very long
as compared with the body...I'm a little woried about this...
I know that it's very hard to identify the exact species, but I would
like to know, at least, the family (I mean xanthidae, mitrhax and so
on) or if, in your experience, crabs could be considered reef-safe.I
know, for example, that xanthidae are not reef-safe.
Just another info: I've seen many "skeleton's crab" (sorry but I dont'
know the exact word) in the tank, so the crab it's growing up.

Bye and sorry for the length of the post.