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.
Archaebacteria belong to the Domain Archaea and are single-celled organisms that tend to live in extreme environments, like hot springs or in high-salt regions. In fact, these organisms boldly go where others cannot! They have been called extremophiles, which means lover of extremes. Methanogens: These archaea release methane gas, hence the name. 2  These extremophiles are found in anaerobic habitats, or places without oxygen. 3  They can be found in your intestines as well as the guts of cows.