It is illegal to take any "live" shells from any Florida beach. "Live" shells are those in which a creature lives, whether the occupant is the original "owner" or not. So if any critter is visible, gently place the shell back in the sand.
This applies to sand dollars and starfish, as well. If you pick up either a sand dollar or a starfish, turn it over and very, very gently run your finger across its alveolae, or tiny "tentacles". If these "tentacles" move at all on their own, the starfish or sand dollar is still alive, and you should gently place it back in the surf.
where in florida do you live I would like to personally check their codes