Weakly electric fish (IMAGE) Michigan State University Caption The sperm of the mormyrid wealy electric fish is the only known vertebrate species that lacks flagellum. Panel A shows a light microscope image of a sperm sample: the sperm are completely immotile. Panel B shows a scanning electron microscope image of a single sperm cell. Credit Jason Gallant, Michigan State University Usage Restrictions Credit must be given to the creator. Adaptations must be shared under the same terms. License CC BY-SA 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.