the hard, variously colored, calcareous skeleton secreted by certain marine polyps. 2. such skeletons collectively, forming reefs, islands, etc. 3. the solitary or colonial polyp that secretes this calcareous skeleton.
There are three major known groups of Archaebacteria: methanogens, halophiles, and thermophiles. The methanogens are anaerobic bacteria that produce methane. They are found in sewage treatment plants, bogs, and the intestinal tracts of ruminants.
Hydrothermal Vent Archaea. One example in the Archaea domain is Methanocaldococcus jannaschii, currently classified as Archaea: Euryarchaeota: Methanobacteria; Methanobacteriales: Methanobacteriaceae, Methanocaldococcus, and species jannaschii.ence, archaebacteria is an outdated term, and they are now classified in the Archaea domain. Classifications within this domain are unofficial due to debates over the descendancy of microbes.