ID blue hitch hiker crab?

I attached a picture ... Not sure if it worked though
Let me know
But it's a small blue crab about an inch in diameter and only comes out at night

 

It looks like a Porcelain (Neopetrolisthes ohshimai) crab type, there is also a blue variation. Should be harmless if the ID is correct.

Edit: Link added

http://www.liveaquaria.com/product/prod_display.cfm?c=497 501 1963&pcatid=1963

 

Thanks
Any other thoughts still
And also how small can a porcelain crab be ... Because I check my tank almost every night and I've only noticed him these past two weeks and he molted once

 

Many crab species start in a free-swimming planktonic larval stage, along with sponges, urchins, land hermits, and a rather large host of other critters. Im not certain whether the porcelain hatches as a crab or has to settle out of the mix to morph, but it would still be quite tiny either way- small enough to hide in a crack or hole in a rock.