Pencil Urchins have long sturdy spines, but are not sharp, and are safe to handle. They eat detritus, and are excellent additions to your clean up crew. They can grow to roughly 5", but we sell them anywhere from 1"-3". If you have a specific size you need, please let us know when ordering. Also, make sure your rock formations are sturdy, as they move around alot, especially at night, and can knock over loose rocks and corals.