Mantis Shrimp Question

[Floop70]

I just got a small green mantis shrimp. I *think* it's a Gonodactylellus viridis but I don't really know for sure. It looks pretty much like the green one. It's about 1 inch long. Since I got it last night it seems to be laying on it's back and kicking it's feet. Hasn't moved since I put it in. Do they do this when they are stressed? Might it come around?

It's currently in probably a 1.5 - 2 gallon "tank" with a piece of live rock and some sand. There is currently no filtration but I do have an air stone in there to provide oxygen for it. I would likely buy a larger tank (5 - 10 gal or so) but I don't really want to put up the cash until I think he's gonna live.

Any suggestions?

Thanks
Bruce