Archaea Definition and Examples - Biology Online Dictionary

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Archaea are the unicellular prokaryotes that comprise the domain of the same name, Archaea. These microorganisms are typically found inhabiting and thriving in extreme environmental conditions. They include the halophiles (archaea inhabiting extremely salty environments), methanogens (archaea producing methane), and thermophiles (archaea that thrive in scorching environments).

Archaea definition

Halobacterium sp. strain NRC-1, an archaeon species. In this photo, the cells of Halobacterium sp. strain NRC-1 are in a cluster.

Archaea refers to the microorganisms that physically resemble the bacteria but are genetically distinct from the latter.

Etymology

The term archaea (ar-KAY-ə) (singular: archeon) came from Greek arkhaion, arkhaios, meaning “ancient”. Synonyms: archaebacteria. Compare: eubacteria.

Characteristics

Archaea or archaebacteria evolved separately from eubacteria and eukaryotes. They are similar with eubacteria in being prokaryotes and lacking distinct cell nucleus. They differ in terms of ribosomal structure, the possession of introns (in some species) and in membrane structure or composition. They are similar to eukaryotes in ways that archaea possess genes and several metabolic pathways that are more closely related to those of eukaryotes: notably the enzymes involved in transcription and translation.⁽¹⁾
They are regarded to be living fossils and survivors of an ancient group of organisms that bridged the gap in evolution between eubacteria and eukaryotes.