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 --Prokaryotic, unicellular, nutrition by absorption (heterotrophic). This group of bacteria-like organisms live in harsh (high temperature, salinity, etc.) environments similar to that of ancient earth (hence the name). They cell wall structure is different than that of typical bacteria.