Internal Structure of Chromatophores (image) Harvard University Caption Chromatophores were previously thought to be simply sacs of pigment that acted as filters; scientists have now discovered that nanostructures (labeled here as "granules") within the cells are capable of fluorescing. Credit Images courtesy of George Bell, Marine Biological Laboratory. Usage Restrictions Must give credit. 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.