I have been watch a hitckhiker crab that came with my rock....Will have pics tonight.
Growing up crabbing for blue crabs I know the difference between males and females and this one is a female and under her belly near the back there is a flap and under it is a bunch of lil eggs
It is so cool to watch her. Can't wait to see these lil guys. As far as I can tell....these guys are harmless crabs....even though they have rather big claws. They seem to feed by 2 fan legs they grab lil things in the water and they scoop it in their mouth...and have a greenish color. Maybe Emerade crab?