Benthic Foraminifera . U.S. Geological Survey. An introduction to fossil Foraminifera. The diatoms are members of the Chromista branch of the Protista. The diatoms are characterized by a double outer shell like a box with a matching lid composed of silicon.
Diatoms are aquatic and occur in both fresh and marine environments.
The diatoms occur in the fossil record from the Cretaceous to the present. A general introduction to diatoms and their commercial uses. University of California at Berkeley Museum of Paleontology. An introduction to the geological history of the diatoms. U.S. Geological Survey.