What am I

                             I swim in the sea

                              I have no brains

           I can survive over five hundred million 
                                       years

     I live about one hundred nautical miles       
             away from Cairns and Australia

  

       My body is about ninety five per cent of 
                                         water

                                        

                                    What am I?
                               

          Please leave me a comment to see what you think I am good luck