The Pencil Urchin, Eucidaris tribuloides, is a small, spherical hard shelled sea animal covered in mildly poisonous protective spines. This species eats primarily algae and detritus but will take additional supplemental feedings. Care should be had if they are kept with corals as they can sometimes trample over them.  The Pencil Urchin is best kept in a tank with plenty of live rock as it will scavenge at night for its food moving freely around the tank.