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 Arachnoidiscales Round (1990) Family Arachnoidiscaceae Round (1990) Genus Arachnoidiscus H. Deane pat. ex Shadbolt (1852)