The 'Aigarchaeota' are a proposed archaeal phylum of which the main representative is Caldiarchaeum subterraneum. It is not yet clear if this represents a new phylum or a thaumarchaeal order, since the genome of Caldiarchaeum subterraneum encodes several thaumarchaeal features. The name 'Aigarchaeota' comes from the Greek αυγή, ‘aigi’, meaning dawn or aurora, for the intermediate features of hyperthermophilic and mesophilic life during the evolution of its lineage.
Martijan, Joran; Ettema, Thijs J. G. (February 2013). "From archaeon to eukaryote: the evolutionary dark ages of the eukaryotic cell". Biochemical Society Transactions. 41 (Part 1): 451–457. PMID23356327. doi:10.1042/BST20120292.
Yutin, Natalya; Koonin, Eugene V. (April 2014). "The Dispersed Archaeal Eukaryome and the Comple Archaeal Ancestor of Eukaryotes". Cold Spring Harbor Perspectives in Biology. 6 (4): Article No.: a016188. doi:10.1101/cshperspect.a016188.