Variegated Urchin (Lytechinus variegatus) – Blue Heron Bridge, Riviera Beach, FL
In this shot you can see both the rigid spines of the urchin (used for protection) as well as the soft tube feet (used for movement across the bottom).
Canon G15, Nauticam NAG15, Inon s2000 (x2), Sola Photo 800, Nauticam CMC-1
1/100 sec, f/6.3, ISO100