Me.tha.no.coc.co'i.des. Gr. adj. suff. ‐oides similar to; N.L. neut. n. Methanococcoides organism similar to Methanococcus. Euryarchaeota / Methanomicrobia / Methanosarcinales / Methanosarcinaceae / Methanococcoides The genus Methanococcoides comprises four species, Methanococcoides methylutens, Methanococcoides burtonii, Methanococcoides alaskense, and Methanococcoides vulcani. Cells are irregular cocci, 0.5–3 μm in diameter, occurring singly or in pairs, and may be motile. Clumps of cells can also observed. Cells exhibit a blue‐green autofluorescence under UV illumination. The cell wall consists of a very thin protein S‐layer, approximately 10‐nm thick. Susceptible to lysis by hypotonic or detergent shock. Eurypsychrophilic to mesophilic. Strict anaerobe. Neutrophilic. Halophilic, optimal salinity near seawater. Cells can dismutate methylamines, methanol, glycine betaine, choline, tetramethylammonium, dimethyl sulfide, methyliodide, and N,N‐dimethylethanolamine for growth, but cannot catabolize acetate, dimethylsulfide, H2/CO2, or formate. Methanococcoides spp. are members of the phylum Euryarchaeota, class Methanomicrobia, order Methanosarcinales, and family Methanosarcinaceae. Known habitats are deep‐sea mud volcano, marine anoxic sediment, hypolimnion Ace Lake, mangrove swamp, deep hypersaline anoxic basin, and hydrothermal vents. DNA G + C content (mol%): 40.8–44. Type species: Methanococcoides methylutens Sowers and Ferry 1983, VL17.