Crab ID

[grouper25]

I found a bizarre 4" crab sitting in my 75 gallon reef tank last evening while looking in the dark. It has red eyes and green squares on its back and something I have never seen. It has to have been there for a while and came as a hitchhiker. I have seen no damage to any coral and my Blood shrimp is fine along with snails. It will be hard to ever trap or find him so he may be staying.

Does anyone know a resource I could look at to try to match him up. I cant take apic cause he hides in a very dark hole in the rock.

Thanks