That was a pretty big one... Maybe 10 inches across or more? We see them all the time here. All of my diving pictures are off the coast of south Florida.
Jealous! I went diving off Duck Key last May - one of my greatest experiences. Didn't have my camera nor underwater housing then...
I saw a dolphin (lucky enough to see it underwater!), and a pretty big Lemon Shark, and of course millions of others. I hope to go back sometime soon!
Really nice shot. I really want to get into underwater photography.