because the crab needs the sea urchin for protection and the sea urchin needs the crab for food
The classification of a Sea Urchin is Echinoidea
sea urchin
A sea urchin does move, but not very frequently.
they need salt water and never trust this sit.
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. :(
a blue tuxedo sea urchin
Spines of the sea urchin can cause injuries of the skin.
It urges the sea to adapt to IT! The litle urchin urger.
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.
kelp crab is stronger