I have a spotted puffer and a N iger, they are both small, about 1.5-2 inches. They do not bother my snails or crabs, do you think they would eat a pencil urchin? If they did would there be any ill side effects besides a dead urchin?
Ive read that some urchins can cause health problems if eaten. Ill look into it more and get back to you. Maybe not until I get back from my trip on Sunday.