A recent metagenome study by Evans et al., (2015) has detected the presence of a divergent mcrA gene sequence in Bathyarchaeota (formerly Miscellaneous Crenaorchaeotal group).
This has very strong implications such as :
-not only members of the Euryachaeota phylum are able to perform methanogenesis
-a version of mcrA existed in the Bathyarchaota and Euryarchaeota common ancestor
-new primers should be used to take into account the divergent Bathyarchaota mcrA gene to analysie methanogenesis, in the marine realm, and also in lacustrine ecosystems.
-these Bathyarchaeota can do a lot of amazing things (see Lloyd et al., 2013 & Meng et al., 2014)
here is the paper :
and here is a nice overview of the story :(where the figure below comes from)
Lloyd, K. G., Schreiber, L., Petersen, D. G., Kjeldsen, K. U., Lever, M. A., Steen, A. D., ... & Jørgensen, B. B. (2013). Predominant archaea in marine sediments degrade detrital proteins. Nature, 496(7444), 215-218.