Here are two crabs I found while taking down my tank. The funny thing about these crabs is they must have come in very tiny as hitchhikers. I rarely buy any large colonies on rocks. Most everything I have bought is on a small chunk of rock or frag plug.
Any idea what kind they are? (Thanks to Beakerbob for taking the pics!)
First crab....black...but looks like a mutant emerald crab. Is it possible that an emerald morphed from green to black?
Second crab...almost had the tank completely emptied and noticed a little movement on the bare bottom. Little sucker "curled" right up and grabbed onto some polyps and didn't want to release. Finally got him to let go. Maybe a gorilla crab?