I can tell you what that is, and I'm sorry if it has been answered in the previous posts...didn't look.
That is a FEMALE Cherax Quadricarinatus!
They have great personality's, can be aggressive and like to hide a lot.
Make sure you get plenty of Oxygen into the water, throw some eggshells in for hardness, and they'll eat it as needed after they moult.
And they are sensitive to Nitrates.
Other that that, after she moults after eating some good food she should color up some.They also put on a striking bluish green color when scavaging at night.