The Variegated Sea Urchin grows to 4 inches in diameter regularly in captivity. It spines stretch it out to nearly 5 inches in diameter. Because of its large size it can/will be a bulldozer around small coral frags. They also like to wear loose objects, (including snails and hermits), as camouflage. Putting empty shells on them to wear reduces this tendency. They will mow down any and all edible macroalgae as they grow. Their definition of edible algae is pretty expansive, and they eat calcified algae as well.
This species can scratch acrylic tanks.