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 Groups. Under the kingdom Archaea, archebacteria are classified into the following phyla: Methanogens harvest energy by converting H2 and CO2 into methane gas. They are found in the intestinal tracts of humans and some animals such as cows, and in marshes.