Primitive single-celled organisms thought by some to be the oldest life-forms on Earth. They were first known for their ability to survive in a range of extreme environments, such as salty water, hot springs, and sulfur vents at the bottom of the ocean floor, though further research also finds Archaea in a variety of non-extreme environments.

There is some disagreement as to how the Archaea should be classified. They were originally categorized as a sub-group of Bacteria, but they have very few similarities with them. Some taxonomies place them in a domain of their own, based on the differences between their genetic code and those of the Eukaryotes and Prokaryotes. Others place them within the Monera. Thus, the main divisions within the Archaea (Crenarchaea, Euryarchaeota, and sometimes others such as Korarchaeota and Nanoarchaeota) are variously described as kingdoms, phyla, or even classes.

Subcategories 2

Related categories 1

Archaea
Introduction to this life form, written at three different levels of complexity for use by educators and students.
The Archaea
General introduction, mentioning most known genera and species of Euryarchaeota and Crenarchaeota. Includes some technical details such as toxin sensitivities.
Archaea
Open access journal devoted to original research on the Archaea. Author guide, publication schedule, and text of older articles.
Archaea (Archaebacteria)
Taxonomy, description, and extensive references, with particular emphasis on the Crenarchaeota (classified here as a Kingdom.)
Horikoshi Superbugs
Summary of interesting organisms discovered during a search for extremophiles, including a picture of the triangular halophile Haloarcula japonicus.
Introduction to the Archaea
Covers their main groupings, chemical differences from other life forms, fossil record, and the structure of their cell walls.
Open Questions: Archaea and Extremophiles
Annotated list of recommended sources.
Procaryotic Life
Online textbook chapter from the University of Wisconsin, discussing the origin of life and touching on some of the molecular characteristics that separate the domains, Archaea and Bacteria.
Taxonomy Browser (Archaea)
Shows the relationships among the recognized groups, and samples yet to be named or classified.
Wikispecies: Archaea
Taxonomy browser, with some links.
German Jurgens: Molecular phylogeny of Archaea in boreal forest soil, freshwater and temperate estuarine sediment
Academic thesis on the unexpected organisms discovered by ribosomal analysis of non-extreme soil and water samples. (October 14, 2002)
Genome News Network: New Amino acid Discovered in Methanosarcina barkeri
Reports on the discovery of a new amino acid, pyrrolysine, coded by UAG (normally a stop codon) in this methanogen. (May 25, 2002)
Distribution of Archaea in a Black Smoker Chimney Structure
Analysis of different communities in varied microhabitats of a deep-sea vent. Journal article from Applied and Environmental Microbiology (August 01, 2001)
BBC News: Toughest Bug Reveals Genetic Secrets
Reports the decoding of the Pyrococcus abyssi, which lives in the intense pressure and temperature of black smoker vents on the seafloor. (July 21, 1999)
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