Symbiosis (IMAGE) PNAS Nexus Caption Epi-fluorescent micrograph of a chain of the Hemiaulus-Richelia symbiosis combining brightfield and green excitation to excite the autofluorescence of the Richelia filaments (here shown in yellow). Usually, one or two Richelia symbionts are observed per host diatom. Credit Sepehr Bardi Usage Restrictions None License Original 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.