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.
Euryarchaeota Species: Examples of Euryarchaeotans include: 1  Halobacterium-include several species of halophilic organisms that are found in salt lakes and high saline ocean environments. 2  Methanococcus-Methanococcus jannaschii was the first genetically sequenced Archaean.