Division Bacillariophyta Engl. & Gilg (1919) see Phylum Bacillariophyta Engl. & Gilg (1919)
   Class Coscinodiscophyceae Round & R.M. Crawford (1990) - radial centrics
     Subclass Biddulphiophycidae Round & R.M. Crawford (1990) see Class Mediophyceae Medlin & Kaczmarska (2004)
       Order Hemiaulales Round & R.M. Crawford (1990)
         Family Hemiaulaceae Heib. (1863)
           Genus Riedelia Jousé & Shesh.-Por. (1971), nom. illeg.