They get about 8 Inches it is a Black Spiney Sea Urchin. And that is his butt. My Grand daughter loves his bathroom adventures. They are Venemous but dependent on your reactions, like a bea sting. It will not sting you, you will end up forgetting he is in the corner when you are cleaning and ram a hand into him. Happens to me when I forget about him lurking. For me my knuckles get thick and it burns like Hell for about an hour. Other wise harmeless.