Those are pretty cool!
Now for a story about sea urchins... I am a certified diver... got certified in Maine. Bought a 41" lobster boat with my best friend in 1990 and was a sea urchin diver for 2 years. Got the scars on my knees to prove it (from kneeling in a bed of urchins sweeping them into a bag)
Anyway... those a pretty neat.
Eric