These sea urchins are Variegated Sea Urchins - Lytechinus variegatus. Their range is around Florida and the tropical west Atlantic. Every time I go to Florida I see these urchins, sometimes in the thousands. They can get as big as a tangerine and are usually purple but sometimes pink. I typically find them in sea grass beds but have also seen them on bare sand along the swimming beaches. They eat algae and sometimes cover themselves with blades of the seagrass they are eating as well as shells; perhaps for camouflage.
ORA Variegated Sea Urchins at FJW, both are about the same size as a quarter.
The other ORA Variegated Sea Urchin at FJW, this one is a little darker.
The two ORA Variegated Sea Urchins in my 30 gallon tank. This tank has lots of Caulerpa, Halimeda, and some hair algae for them to graze on if they choose. They are often seen together like in the picture above.
ORA Variegated Sea Urchin - blog post. For more information and some more cool photos of the Urchins developing. Great job ORA! I hope you add some more Florida urchins to your breeding list; perhaps. Long-spinned Urchin - Diadema antillarum or West Indian Sea Egg - Tripneustes ventricosus.