In 1977, a PNAS paper by Carl Woese and George Fox demonstrated that the archaea (initially called archaebacteria) are not significantly closer in relationship to the bacteria than they are to eukaryotes.
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Haeckel's Monera included not only bacterial groups of early discovery but also several small eukaryotic organisms; in fact the genus Vibrio is the only bacterial genus explicitly assigned to the phylum, while others are mentioned indirectly, which led Copeland to speculate that Haeckel considered all bacteria to belong to the genus Vibrio, ignoring other bacterial genera.