Additional File 4. The identity of Thalassiosira pseudonana Previous concepts of Thalassiosira pseudonana Observations from diverse literature sources

Observations from diverse literature sources reveal that diatomists have more-or-less consistently viewed T. pseudonana as a small (less than 10 μm diameter) centric diatom with 0– 3 central area strutted processes, a relatively high number of marginal area strutted processes, and a labiate process situated roughly equidistantly between two marginal area strutted processes [1-7]. Ultrastructural features common to diatoms illustrated by these authors include three satellite pores per marginal area strutted process, the presence of more-or-less prominent cowlings around the strutted process satellite pores, and a more-or-less prominent siliceous ridge (opercle) on the central strutted process tube situated directly above each satellite pore. The labiate process is typically oval in shape.