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, archaebacterium, archaeobacteria, archeobacteria - considered ancient life forms that evolved separately from bacteria and blue-green algae. halobacter, halobacteria, halobacterium - halophiles in saline environments such as the Dead Sea or salt flats.