Anomia ephippium
These shiny 1” to 2” bivalves are named for the bell-like sound made when several shells are shaken. Other names include: Mermaid's toenails, Neptune's toenails, toenail shells, gold shells and saddle oysters.
Beachcombers collect these shells to make wind chimes, jewelry, or to string together for window or door curtains. They have industrial uses in the manufacture of glue, chalk, paint, shellac and solder. The taste is bitter.
Jingle shells are filter feeders, sieving water through their gills to remove plankton. They attach themselves by secreting byssal (filament) threads from a gland that secures them to a hard surface.
The attached half rarely washes up on the beach, but when it does, you will see the "hole" that is left from when the attached shell half was braoken away from the surface it was attached to.
Live shells should never be taken from any Florida State Park.