<P> Parts of the three - domain theory have been challenged by scientists including Ernst Mayr, Thomas Cavalier - Smith, and Radhey S. Gupta . In particular, Gupta argues that the primary division within prokaryotes should be among those surrounded by a single membrane (monoderm), including gram - positive bacteria and archaebacteria, and those with an inner and outer cell membrane (diderm), including gram - negative bacteria . He claims that sequences of features and phylogenies from some highly conserved proteins are inconsistent with the three - domain theory, and that it should be abandoned despite its widespread acceptance . </P> <P> Recent work has proposed that Eukarya may have actually branched off from the domain Archea . According to Spang et al. Lokiarchaeota forms a monophyletic group with eukaryotes in phylogenomic analyses . The associated genomes also encode an expanded repertoire of eukaryotic signature proteins that are suggestive of sophisticated membrane remodelling capabilities . These data suggest a two - domain system as opposed to the classical three - domain system . </P>

Is one of the three most represented phyla