Classification (5):
-Main types:

• Crenarchaeota- tolerate extremes in temperature and acidity
• Euryarchaeota- methane-producers and salt-lovers
• Korarchaeota and Nanoarchaeota- not much is known about these 

-Subgroups:

• Methanogens: produce methane as a waste product of their metabolism
• Halophiles: live in salty environments
• Thermophiles- live at extremely hot temperatures
• Psychrophiles- live at unusually cold temperatures

Size (2):

• Tiny, less than one micron long
• Can be seen with an electron microscope

Methanothermus fervidus, a short bacillus form without flagella (2)

Shapes (2):

• Coccus- spherical

       may be perfectly round or lobed and lumpy

• Bacillus- rod-shaped

       range from short bar-shaped rods to long hair-like forms

• Some are triangular or square

---

Methanobacterium thermoautotrophicum, an elongated bacillus form (2)

Methanosarcina barkeri, a lobed coccus form lacking flagella (2)

Methanococcus janaschii, a coccus form with numerous flagella attached to one side (2)

Cell Accessories (2):

• flagella- the cell may have one or more flagella attached (when multiple, they are only attached at one side of the cell)

          -though may lack flagella altogether

• protein networks- cells are able to anchor together in large groups

Cell Structure (2):

• No internal membranes
• DNA is a plasmid
• In most, a cell wall surrounds the cell membrane; this cell wall is chemically distinct from that of any other organism
• There are 4 fundamental differences between the archaeal cell membrane and those of all other cells:

1. Chirality of glycerol
2. Ether linkage
3. Isoprenoid chains
4. Branching of side chains

Nutrition (3):

Nutritional Type

• Phototroph
• Lithotroph
• Organotroph

Source of Energy

• Sunlight
• Inorganic compounds
• Organic compounds

Source of Carbon

• Organic compounds
• Organic compounds or carbon fixation
• Organic compounds or carbon fixation