Macronuclei are formed by the differentiation of micronuclei, which usually involves some degree of RNA-mediated DNA editing.

O. trifallax is the first species sequenced with an unusually high degree of fragmentation in its macronuclear genome.

The macronuclear genome encodes about 18,500 genes, but these are distributed on 16,000 chromosomes, which are called nanochromosomes due to their length.

Their mitochondria also possess a separate plasmid, which may have been involved in horizontal gene transfer during the evolution of the mitochondrial genome.

It was reclassified as Sterkiella histriomuscorum on the basis of morphological characteristics, but a molecular phylogeny supports the original classification as a species of Oxytricha.