This long spine urchin I got at blue ribbon koi. Originally I got two small ones. One perished fairly shortly after I got them, but this one has lived very well in my system.

He's a voracious algae eater and eats all kinds of algae that he comes across on the rock (including coraline). He's working on the back walls of the tank now.

He's also huge now, spaning probably 7-8". The colorful thing on his top side is actually his anus (I know I've caught him going to the bathroom, wish I'd gotten a pic of it).

His spines are very sharp and posionous. I've been hit by one once, and it's like a bee sting (and yes he left a little piece of himself inside me).