Diatom Thalassiosira pseudonana (IMAGE) University of Washington Caption Thalassiosira pseudonana -- with a hard outer shell of silica shaped like a hatbox and marked with pores -- is 3 to 4 microns in size, making it among the smallest diatoms. New insights into how Thalassiosira pseudonana build their shells is being published online this week in the Proceedings of the National Academy of Sciences. 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.