Short Spine Urchin

(Reef- Sometimes) Urchin that feeds on algae, which may include hair algae. They will not eat corals but could damage delicate types with their spines. They will often pick up items from the tank such as shells, rocks, and coral polyps and decorate their body with those items for camoflage.  (Tripneustes ventricosus or Lytechinus variegatus)