Five isolates of Phaeodactylum tricornutum Bohlin were examined in light and transmission electron microscopes. Although isolated from widely separated sites including both coastal marine and inland saline habitats, the morphology of the siliceous frustules of all isolates was very constant. The fusiform and triradiate forms, which have been reported as being non-siliceous in the past, were found to have an amorphous particulate nature in TEM. These forms were examined using EDAX SEM elemental analysis and were found to contain silica in their cell walls.
Johansen, Jeffrey R.
"Morphological variability and cell wall composition of Phaeodactylum tricornutum (Bacillariophyceae),"
Great Basin Naturalist: Vol. 51
, Article 4.
Available at: http://scholarsarchive.byu.edu/gbn/vol51/iss4/4