Tortotubus Ornament with Envelope (image) University of Cambridge Share Print E-Mail Caption Filament of Tortotubus from the Silurian of Gotland, Sweden, showing envelope of secondary filaments covering main filament and primary branches, and developing a distinctive pustular ornament. Scanning Electron Micrograph. Credit Martin R. Smith Usage Restrictions Please credit to Martin R. Smith Share Print E-Mail 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.