Diatom Coscinodiscus (IMAGE) University of Washington Caption Another species of diatom, Coscinodiscus, has been stained to reveal freshly precipitated silica and its nano-patterned cell wall. The red dots are chloroplasts where photosynthesis occurs. At up to 0.5 mm in diameter, Coscinodiscus are among the largest diatoms. Credit University of Washington Usage Restrictions Photo credit required 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.