I've had my Halloween urchin for close to 2 years. Hasn't hurt a thing He touches my coral and clams all the time (and sometimes my fish eat algae off his back that he's carrying around!). But I did read some think they are toxic, but not proven just how toxic. So always be careful! P.s. I have one in my 40 gallon tank too - have had him for 6 months or so.