The rock urchin is a popular addition to any aquarium with its unique appearance and interesting behaviour. This species can grow up to 3 inches in diameter and requires a diet of algae and other plant matter. With its hardy nature, it is compatible with most aquarium inhabitants. However, caution must be taken with delicate corals, as it can accidentally knock them over. An aquarium of at least 30 gallons is needed to house a rock urchin. Overall, the rock urchin is a great addition to any aquarium looking to add some flair to its decor.