Swimming Ray (IMAGE) University of Plymouth Caption A ray swimming away from the vehicle. The grey ball, left of the ray, is a xenophyophore - the largest known single-celled organism on the planet. Credit University of Plymouth Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.