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.
Size and shape. Both archaea and eubacteria are similar in shape and size. They are both found occurring as rods, cocci, spirals, plates, coiled etc. The general cell structure of archaea and bacteria are the same but composition and organization of some structures differ in archaea.