Introduction The archaeal candidate phylum Aigarchaeota belongs to the TACK superphylum, which initially consisted of the Thaumarchaeota, Aigarchaeota, Crenarchaeota and Korarchaeota phyla (Guy and Ettema, 2011; Adam et al., 2017). The TACK superphylum now comprises several additional phyla discovered since 2011, including Bathyarchaeota (Meng et al., 2014), Verstraetearchaeota (Vanwonterghem et al., 2016), Geothermarchaeota (Jungbluth et al., 2017), and Nezhaarchaeota (Wang et al., 2019).
