(and the higher level classification is rather flat)." This classification treats diatoms as a phylum (Diatomeae/Bacillariophyta), accepts the class Mediophyceae of Medlin and co-workers, introduces new subphyla and classes for a number of otherwise isolated genera, and re-ranks a number of previously established taxa as subclasses, but does not list orders or families. Inferred ranks have been added for clarity (Adl. et al. do not use ranks, but the intended ones in this portion of the classification are apparent from the choice of endings used, within the system of botanical nomenclature employed). Clade Diatomista Derelle et al. 2016, emend. Cavalier-Smith 2017 (diatoms plus a subset of other ochrophyte groups) Phylum Diatomeae Dumortier 1821 [= Bacillariophyta Haeckel 1878] (diatoms) Subphylum Leptocylindrophytina D.G. Mann in Adl et al. 2019 Class Leptocylindrophyceae D.G. Mann in Adl et al. 2019 (Leptocylindrus, Tenuicylindrus) Class Corethrophyceae D.G. Mann in Adl et al. 2019 (Corethron) Subphylum Ellerbeckiophytina D.G. Mann in Adl et al. 2019 (Ellerbeckia) Subphylum Probosciophytina D.G. Mann in Adl et al. 2019 (Proboscia) Subphylum Melosirophytina D.G. Mann in Adl et al. 2019 (Aulacoseira, Melosira, Hyalodiscus, Stephanopyxis, Paralia, Endictya) Subphylum Coscinodiscophytina Medlin & Kaczmarska 2004, emend. (Actinoptychus, Coscinodiscus, Actinocyclus, Asteromphalus, Aulacodiscus, Stellarima) Subphylum Rhizosoleniophytina D.G. Mann in Adl et al. 2019 (Guinardia, Rhizosolenia, Pseudosolenia) Subphylum Arachnoidiscophytina D.G. Mann in Adl et al. 2019 (Arachnoidiscus) Subphylum Bacillariophytina Medlin & Kaczmarska 2004, emend. Class Mediophyceae Jouse & Proshkina-Lavrenko in Medlin & Kaczmarska 2004 Subclass Chaetocerotophycidae Round & R.M. Crawford in Round et al. 1990, emend. Subclass Lithodesmiophycidae Round & R.M. Crawford in Round et al. 1990, emend. Subclass Thalassiosirophycidae Round & R.M. Crawford in Round et al. 1990 Subclass Cymatosirophycidae Round & R.M. Crawford in Round et al. 1990 Subclass Odontellophycidae D.G. Mann in Adl et al. 2019 Subclass Chrysanthemodiscophycidae D.G. Mann in Adl et al. 2019 Class Biddulphiophyceae D.G. Mann in Adl et al. 2019 Subclass Biddulphiophycidae Round and R.M. Crawford in Round et al. 1990, emend. Biddulphiophyceae incertae sedis (Attheya) Class Bacillariophyceae Haeckel 1878, emend. Bacillariophyceae incertae sedis (Striatellaceae) Subclass Urneidophycidae Medlin 2016 Subclass Fragilariophycidae Round in Round, Crawford & Mann 1990, emend. Subclass Bacillariophycidae D.G. Mann in Round, Crawford & Mann 1990, emend. See taxonomy of diatoms for more details. Gallery Three diatom species were sent to the International Space Station, including the huge (6 mm length) diatoms of Antarctica and the exclusive colonial diatom, Bacillaria paradoxa. The cells of Bacillaria moved next to each