Kingdom Protoctista Hogg, 1860
   Phylum Bacillariophyta Engl. & Gilg (1919) - diatoms see [unranked] Diatomea Kütz. (1844)
     Class Coscinodiscophyceae Round & R.M. Crawford (1990) - radial centrics
       Subclass Coscinodiscophycidae Round & R.M. Crawford (1990)
         Order Coscinodiscales Round & R.M. Crawford (1990)
           Family Hemidiscaceae Hendey (1937)
             1 Genus Actinocyclus Ehrenb. (1837)
             2 Genus Hemidiscus G.C. Wall. (1860)
             3 Genus Roperia Grunow ex Pelletan (1889)