Pleuromastigaceae is an obsolete family of cryptomonads, which included genera Monomastix, Pleuromastix, and Xanthodiscus.
Today, Monomastix is regarded as a green alga, and since 1987 Xanthodiscus is regarded as a synonym of Prorocentrum.
[1][2] Pleuromastix remains unclassified as a part of any larger taxon as of 2019.
[3]