Emerald Crab?

[MyBoyGus]

It seems to have antenna. It hides in a leg holding up the eggcrate of my frag tank. When I approach the tank, it quickly hides into the leg. Wish I could have taken better photos. The main part of the thing seems to be behind the legs, like a spider. Any ideas? Thank you.

 

[revhtree]

Hard to tell. Looks weird for some reason. LOL!

 

[UltimateReefer115]

Could be a hermit crab with no shell.

 

[KoleTang]

Try catching it and examining it. Never trust a crab.