Obscure crab - please help with ID

[Hexabonal]

I can't find the ID of this crab anywhere. I thought it was a mithrax and bought four of them for $2 each, but it's not. Here in Hong Kong the shopkeepers do not speak English and all kinds of obscure things come up for sale. It's about an inch wide.The eyes are on stalks. They're very calm and do not move a lot. I have four of them in the sump. This one has purple legs but others have red legs. Part of me is wondering if it's not truly a marine crab as I can't find any information about them.

(Apologies for the second thread if you saw my other one, the title and first post were confusing and I wasn't getting any replies)

 

[W1ngz]

I wonder if it's an under water species. Could be intertidal or amphibious.
Any chance you have a small tank you can set up a paludarium of sorts with sand piled to one side, water on the other to see what they do?

 

[Hexabonal]

I wonder if it's an under water species. Could be intertidal or amphibious.
Any chance you have a small tank you can set up a paludarium of sorts with sand piled to one side, water on the other to see what they do?

They seem very happy out of the water, one climbed up a pipe and was happy sat on top of it.

 

[Hemmdog]

I wonder if it's an under water species. Could be intertidal or amphibious.
Any chance you have a small tank you can set up a paludarium of sorts with sand piled to one side, water on the other to see what they do?

+1 looks amphibious.

 

[W1ngz]

After a bit of google-fu I'm gonna guess juvenile orange fiddler crabs. Probably female, apparently only the males have the one big claw.