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.
1 2. 2  ARCHAEBACTERIA â¢ Archaebacteria are the oldest organism living on Earth. 3  They are unicellular prokaryotes-microbes without cell nucleus and any other membrane-bound organelles in their cells-and belong to the kingdom, Archaea. ARCHAEBACTERIA â¢ Archaebacteria are the oldest organism living on Earth. 2  They are unicellular prokaryotes-microbes without cell nucleus and any other membrane-bound organelles in their cells-and belong to the kingdom, Archaea. 3  They were first discovered in 1977 by Carl Woose and George E. Fox and classified as bacteria.