Sea urchins can make interesting pets, especially the pincushion urchins. They stay relatively small and their spines aren’t as sharp as those from other species. Pincushion urchins have tube feet, much like those of a sea star, which are used for locomotion and grabbing small items for camouflage. It’s not uncommon for one of these urchins to have several shells, rocks, and even coral frags on their backs. This trait makes them both desired and annoying. Aquarists are always looking for something interesting, but it can be frustrating when your expensive Zoa frag just walks off.