Bacillariophyta Engl. & Gilg (1919) see Phylum Bacillariophyta Engl. & Gilg (1919)
   Coscinodiscophyceae Round & R.M. Crawford (1990) - radial centrics
     Thalassiosirophycidae Round & R.M. Crawford (1990) see Class Mediophyceae Medlin & Kaczmarska (2004)
       Thalassiosirales Glezer & I.V. Makarova (1986)
         Stephanodiscaceae Glezer & Makarova (1986)
           Cyclotella (Kütz.) Bréb. (1838)