I have had a long spine orange ringed urchin in my tank for almost 3 years. Always did good at grazing on the unwanted algae (did nothing for coraline), but ate any decorative plant I tried to put in, halidmia, money plant, shaving brush...you name it. But recently in the last month I saw it ate one nuclear green button polyp but then left the rest alone (colony of maybe 50), then it found my beloved new papaya clove colony and shaved about half off (arghh...sorry the sauce), had to take a stick and poke him away and move them...but that is the only downside in 3 yrs...center ball body is about 3" outer spikes extent to 10"+...be careful with some fish with vision problems they can accidently run into the spikes...even some of my fish had to learn the hard way, but only did it once. On the other hand a few even smarter fish love to swim inbetween the spikes...cling fish make a great urchin accessory...oh, and it seems every time I put my hand in the tank to do something it likes to be right in the middle of where I want to go...lol...I taped a few chop sticks together and I barely tap a few of the spines (it doesnt take much coaxing, when spines are touch they move very readily) when I need it to move where I need to work (which is not that often)...watch those spines, they hurt...I love having the urchin in my tank, amazing species to watch especially when its up on the front glass to see the underside....Fire urchin are absolutely beautiful, but the spine are 2x if not more poisonous...blue tuxedos usually eat more coraline an other algae than tanks can provide so you will need to provide extra nori for it consistantly... hope this helps