This is Peanut the turtle, shortly after being found in Missouri in 1993. She was taken to to a zoo in St. Louis where the six-pack ring was removed.
It seems that she was trapped in the plastic ring as a young turtle and was unable to free herself. Subsequently her shell moulded itself to the plastic ring and she grew in the strange shape you see here.
Unfortunately the damage is permanent, but peanut is expected to live a long life and today she serves as a mascot for the fight against beach littering.
Please, always remember to clean up after yourself at the beach.