Sea Urchins are widely known for their ability to rid nuisance algae.  They are commonly seen on the sand bed or in the live rock, making their way around, constantly cleaning up leftover fish food and algae.  Sea Urchins are very popular due to their friendly nature, not bothering other sea life and they do well in most conditions.   They are easy to identify as they have a round center with spines which it uses to move around but also as protection from predators.