A　novel　mesophilic,　hydrogenotrophic　methanogen,　strain　CWC-01T,　was　isolated　from　the　sediment　sample　of　the　piston　core　collected　at　station　3　at　Good　Weather　Ridge　area　offshore　southwestern　Taiwan　from　ORI-902A　cruise　in　2009.　Cells　of　strain　CWC-01T　are　rod-　shaped,　measuring　0.4-0.5　mu　m　in　width　and　1.0-2.0　mu　m　in　length.　Strain　CWC01T　utilizes　formate　and　H2/CO2　to　produce　methane,　but　not　secondary　alcohol,　methanol,　ethanol,　methylamines　or　acetate　as　catabolic　substrates.　The　optimal　growth　conditions　are　37　degrees　C,　0.043　M　NaCl　and　pH　6.3.　Growth　effectors　tests　indicate　tryptone,　but　not　acetate　and　yeast　extract,　could　stimulate　the　growth　of　strain　CWC-01.　Phylogenetic　analysis　of　16S　rRNA　gene　reveals　that　strain　CWC-01T　is　most　closely　related　to　Methanobacterium　petrolearium　Mic5c12T,　with　96.63%　identity.　Genome　size　of　strain　CWC-01T　is　1.98　Mb　and　it　is　the　smallest　genome　size　of　genus.　The　genomic　DNA　G+C　content　obtained　from　the　genome　sequence　of　strain　CWC-01T　is　44.15　mol%.　Based　on　these　phenotypic,　phylogenetic　and　genomic　analyses,　we　propose　that　strain　CWC-01T　represents　a　novel　species　in　genus　Methanobacterium,　for　which　the　name　Methanobacterium　aridiramus　sp.　nov.　is　proposed.　The　type　strain　is　CWC-01T　(=BCRC　AR10053T=NBRC　113991T).