Urchin
the only one i no is urchin like a sea urchin
A (street) urchin is a child who lives on the street, surviving by engaging in petty crimes. A (sea) urchin is a spiny creature (exoskeleton), with a soft interior. I welcome improvements to this answer.
Its not.
a Caribbean sea creature
The classification of a Sea Urchin is Echinoidea
sea urchin
A sea urchin does move, but not very frequently.
because the crab needs the sea urchin for protection and the sea urchin needs the crab for food
It is a kind of sea bird.
Ummm...it's the thing from which a sea urchin hatches?
I think a sea anenome and a sea urchin can live together because i have a little aquarium and there is a sea urchin and and a sea anenome (if that's how you spell it) living in there and they were perfectly fine. BUT if you have a sea urchin do not have any crabs in there, because my sea urchin killed one, and almost killed another one by taking its claw off. :(