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Archaea can be round, spiral, rod-, plate- or square-shaped. They range in size from 0.1 to around 15 micrometers. Some Archaea are equipped with long whip-like appendages which facilitate movement.
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Some Archaea live in large colonies that can be made of different types of Archaea.
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Archaea is prokaryote. It doesn't have nucleus and organelles in the cell.
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Cell wall of Archaea doesn't contain peptidoglycan. Some species of Archaea doesn't have cell wall at all and their shape is irregular, ameba-like. Unlike Eubacteria, Archaea do not form spores.
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Based on the structure of DNA and RNA molecules, enzymes involved in translation and transcription and several metabolic pathways, scientists concluded that eukaryotic cell evolved from Archaea (Archaea are Eukaryotes are more similar genetically than Archaea and Bacteria).
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Archaea appeared on the planet few billion years ago, hence the name "Archaea" ("ancient things" in Greek).
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Most species of Archaea still live in the conditions that were typical for Earth 3.5 billion years ago (hydrothermal vents and sulfuric waters).
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Some Archaea live in aerobic, while others live in anaerobic conditions (without oxygen).
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Thermophiles are types of Archea that can be found in habitats with extremely high temperature (of up to 89 degrees of Celsius). Psychrophiles are types of Archea that can be found in the areas with extremely low temperature such as polar seas.
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Some Archaea, such as methane-producing Archaea that can be found in the guts of human and ruminants, consume organic compounds. They absorb waste products from the gut and eliminate methane as by-product. Methane-producing Archaea are frequently used in sewage treatment and for the production of biogas.
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Some other types of Archaea produce energy from inorganic substances such as ammonia and nitrogen and sulfur compounds. They are mostly found in the hot springs.
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Acidophilic Archaea inhabit extremely acidic areas (pH 0). They are often used for the extraction of copper, gold and cobalt from the ores.
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Haloarchaea live in areas with increased concentration of salt in the soil and water. They absorb light using pigment bacteriorhodopsin and produce energy in the form of ATP.
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Pathogenic and parasitic forms of Archaea are not known (Archaea are not harmful for humans).
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Archaea reproduce asexually by fragmentation and binary fission.
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