The urchins are 5-way symmetrical: here you can see the five teeth which are at the base of the animal. He is sticking to the glass with brown threads, a few of which are just visible (near 12:00 and 10:00). The pencil shaped spines can be seen around the body.
As seen from above, you can see the entire creature. A bubble coral is in the upper left, and a fox in the upper right. While the urchin was not destructive, it was a bit clumsy, and after a few months of picking up specimens which had been tipped over, it too went back to the store.