What type of urchin do you have? We are now critter sitting for a couple three months for a buddy while he moves house and stuff. One of the critters is a blue tuxedo pincushion urchin. His spines are covered with shells and all sorts of things he's managed to find in his travels, normal behavior, tonight's the first night we located where he was grazing (an extremely thick coraline encrusted area) so we'll see what he found tasty in the morning.