These echinoids have no arms like their starfish relatives—instead they have spines. Most eat green and brown algae and many will even eat coralline algae, so the reef enthusiast needs to be sure to do his or her homework. Urchin
These echinoids have no arms like their starfish relatives—instead they have spines. Most eat green and brown algae and many will even eat coralline algae, so the reef enthusiast needs to be sure to do his or her homework. Urchins are also capable of stinging the careless hobbyists, and as such, they do require additional care when handling.