Life form (also spelled life-form or lifeform) is an

entity An entity is something that exists as itself, as a subject or as an object, actually or potentially, concretely or abstractly, physically or not. It need not be of material existence. In particular, abstractions and legal fictions are usually r ...

that is

living Living or The Living may refer to: Common meanings *Life, a condition that distinguishes organisms from inorganic objects and dead organisms ** Living species, one that is not extinct *Personal life, the course of an individual human's life * ...

, such as plants (flora) and animals (fauna). It is estimated that more than 99% of all species that ever existed on Earth, amounting to over five billion species, are extinct.

Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surf ...

is the only celestial body known to harbor life forms. No form of extraterrestrial life has ever been discovered.

Archaea

* Archaea – a domain of single-celled microorganisms, morphologically similar to bacteria, but they possess genes and several metabolic pathways that are more closely related to those of eukaryotes, notably the enzymes involved in transcription and translation. Many archaea are extremophiles, which means living in harsh environments, such as hot springs and salt lakes, but they have since been found in a broad range of habitats. **

Thermoproteota The Thermoproteota (also known as crenarchaea) are archaea that have been classified as a phylum of the Archaea domain. Initially, the Thermoproteota were thought to be sulfur-dependent extremophiles but recent studies have identified characteri ...

– a phylum of the Archaea kingdom. Initially ***

Thermoprotei The Thermoprotei is a class of the Thermoproteota. Phylogeny The currently accepted taxonomy is based on the List of Prokaryotic names with Standing in Nomenclature (LPSN) and National Center for Biotechnology Information (NCBI). Referenc ...

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Sulfolobales In taxonomy, the Sulfolobales are an order of the Thermoprotei. Phylogeny The currently accepted taxonomy is based on the List of Prokaryotic names with Standing in Nomenclature (LPSN) and National Center for Biotechnology Information (NCBI) ...

– grow in terrestrial volcanic hot springs with optimum growth occurring **

Euryarchaeota Euryarchaeota (from Ancient Greek ''εὐρύς'' eurús, "broad, wide") is a phylum of archaea. Euryarchaeota are highly diverse and include methanogens, which produce methane and are often found in intestines, halobacteria, which survive ex ...

– In the taxonomy of microorganisms ***

Haloarchaea Haloarchaea (halophilic archaea, halophilic archaebacteria, halobacteria) are a class of the Euryarchaeota, found in water saturated or nearly saturated with salt. Halobacteria are now recognized as archaea rather than bacteria and are one of ...

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Halobacteriales In taxonomy, the Halobacteriales are an order of the Halobacteria, found in water saturated or nearly saturated with salt. They are also called halophiles, though this name is also used for other organisms which live in somewhat less concentrated ...

– in taxonomy, the Halobacteriales are an order of the Halobacteria, found in water saturated or nearly saturated with salt. ***

Methanobacteria In taxonomy, the Methanobacteria are a class of the Euryarchaeota. Several of the classes of the Euryarchaeota are methanogens and the Methanobacteria are one of these classes. Applications Methanobacteria can be used in biomass conversion as ...

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Methanobacteriales In taxonomy, the Methanobacteriales are an order of the Methanobacteria. Species within this order differ from other methanogens in that they can use fewer catabolic substrates and have distinct morphological characteristics, lipid compositions, ...

– information including symptoms, causes, diseases, symptoms, treatments, and other medical and health issues. ***

Methanococci Methanococci is a class of methanogenic archaea in the phylum Euryarchaeota.See the NCBIbr>webpage on Methanococci Data extracted from the They can be mesophilic A mesophile is an organism that grows best in moderate temperature, neither ...

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Methanococcales In taxonomy, the Methanococcales are an order of the Methanococci. Phylogeny The currently accepted taxonomy is based on the List of Prokaryotic names with Standing in Nomenclature (LPSN) and National Center for Biotechnology Information ...

aka ''

Methanocaldococcus jannaschii ''Methanocaldococcus jannaschii'' (formerly ''Methanococcus jannaschii'') is a thermophilic methanogenic archaean in the class Methanococci. It was the first archaeon to have its complete genome sequenced. The sequencing identified many genes ...

'' – hermophilic methanogenic archaea, meaning that it thrives at high temperatures and produces methane ***

Methanomicrobia In the taxonomy of microorganisms, the Methanomicrobia are a class of the Euryarchaeota. Phylogeny The currently accepted taxonomy is based on the List of Prokaryotic names with Standing in Nomenclature (LPSN) and National Center for Biotechnol ...

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Methanosarcinales In taxonomy, the Methanosarcinales are an order of the Methanomicrobia. Large amounts of methane are produced in marine sediments but are then consumed before contacting aerobic waters or the atmosphere. Although no organism that can consume met ...

– In taxonomy, the Methanosarcinales are an order of the Methanomicrobia ***

Methanopyri In taxonomy, the Methanopyri are a class of the Euryarchaeota.See the NCBIbr>webpage on Methanopyri Data extracted from the References Further reading Scientific journals * * Scientific books * * Scientific databases External ...

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Methanopyrales In taxonomy, the Methanopyrales are an order of microbes within the class methanopyri. It contains only one family, Methanopyraceae, one genus, Methanopyrus, and one species, Methanopyrus kandleri. This species is chemolithoautotrophic and its ...

– In taxonomy, the Methanopyrales are an order of the methanopyri. ***

Thermococci In taxonomy, the Thermococci are a class of microbes within the Euryarchaeota.See the NCBIbr>webpage on Thermococci Data extracted from the They live in extremely hot environments, such as hydrothermal vents, and they have optimal growt ...

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Thermococcales In taxonomy, the Thermococcales are an order of microbes within the Thermococci. The species within the Thermococcales are used in laboratories as model organisms. All these species are strict anaerobes and can ferment sugars as sources of car ...

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Thermoplasmata In taxonomy, the Thermoplasmata are a class of the Euryarchaeota. All are acidophiles, growing optimally at pH below 2. '' Picrophilus'' is currently the most acidophilic of all known organisms growing at a minimum pH of 0.06. Many of these o ...

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Thermoplasmatales In taxonomy, the Thermoplasmatales are an order of the Thermoplasmata. All are acidophiles, growing optimally at pH below 2. ''Picrophilus'' is currently the most acidophilic of all known organisms, being capable of growing at a pH of -0.06. M ...

– An order of aerobic, thermophilic archaea, in the kingdom **

Halophiles The halophiles, named after the Greek word for "salt-loving", are extremophiles that thrive in high salt concentrations. While most halophiles are classified into the domain Archaea, there are also bacterial halophiles and some eukaryotic species, ...

– organisms that thrive in high salt concentrations **

Korarchaeota In taxonomy, the Korarchaeota are a phylum of the Archaea. The name is derived from the Greek noun koros or kore, meaning ''young man'' or ''young woman,'' and the Greek adjective archaios which means ''ancient.'' They are also known as Xenarcha ...

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Korarchaeum cryptofilum Archaea ( ; singular archaeon ) is a domain of single-celled organisms. These microorganisms lack cell nuclei and are therefore prokaryotes. Archaea were initially classified as bacteria, receiving the name archaebacteria (in the Archaeba ...

– These archaea have only been found in high temperature hydrothermal environments, particularly hot springs **

Lokiarchaeota Lokiarchaeota is a proposed phylum of the Archaea. The phylum includes all members of the group previously named Deep Sea Archaeal Group (DSAG), also known as Marine Benthic Group B (MBG-B). Lokiarchaeota is part of the superphylum Asgard (archa ...

Methanogens Methanogens are microorganisms that produce methane as a metabolic byproduct in hypoxic conditions. They are prokaryotic and belong to the domain Archaea. All known methanogens are members of the archaeal phylum Euryarchaeota. Methanogens are co ...

Nanoarchaeota Nanoarchaeota (Greek, "dwarf or tiny ancient one") are a phylum of the Archaea. This phylum currently has only one representative, ''Nanoarchaeum equitans''. Taxonomy 53 marker proteins based GTDB 07-RS207 phylogeny. The currently accepted t ...

*** ''

Nanoarchaeum equitans ''Nanoarchaeum equitans'' is a species of marine archaea that was discovered in 2002 in a hydrothermal vent off the coast of Iceland on the Kolbeinsey Ridge by Karl Stetter. It has been proposed as the first species in a new phylum. Strains o ...

'' – This organism was discovered in 2002 and lives inside another archaea. **

Psychrophiles Psychrophiles or cryophiles (adj. ''psychrophilic'' or ''cryophilic'') are extremophilic organisms that are capable of growth and reproduction in low temperatures, ranging from to . They have an optimal growth temperature at . They are found in ...

– (sigh-crow-files) **

Nitrososphaerota The Nitrososphaerota (syn. Thaumarchaeota) are a phylum of the Archaea proposed in 2008 after the genome of '' Cenarchaeum symbiosum'' was sequenced and found to differ significantly from other members of the hyperthermophilic phylum Thermoprot ...

– a phylum of the Archaea proposed in 2008 after the genome of ''

Cenarchaeum symbiosum ''Cenarchaeum symbiosum'' is a species of Archaea in the genus '' Cenarchaeum'', in the phylum Nitrososphaerota in the domain Archaea. ''C. symbiosum'' is psychrophilic Psychrophiles or cryophiles (adj. ''psychrophilic'' or ''cryophilic'') a ...

'' **

thermophilic A thermophile is an organism—a type of extremophile—that thrives at relatively high temperatures, between . Many thermophiles are archaea, though they can be bacteria or fungi. Thermophilic eubacteria are suggested to have been among the ear ...

– (a thermophile is an organism)

Bacteria

Bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were am ...

Gram positive In bacteriology, gram-positive bacteria are bacteria that give a positive result in the Gram stain test, which is traditionally used to quickly classify bacteria into two broad categories according to their type of cell wall. Gram-positive bact ...

no outer membrane ***

Actinomycetota The ''Actinomycetota'' (or ''Actinobacteria'') are a phylum of all gram-positive bacteria. They can be terrestrial or aquatic. They are of great economic importance to humans because agriculture and forests depend on their contributions to soi ...

(high- G+C) ***

Bacillota The Bacillota (synonym Firmicutes) are a phylum of bacteria, most of which have gram-positive cell wall structure. The renaming of phyla such as Firmicutes in 2021 remains controversial among microbiologists, many of whom continue to use the ea ...

(low- G+C) *** Mycoplasmatota (no

wall A wall is a structure and a surface that defines an area; carries a load; provides security, shelter, or soundproofing; or, is decorative. There are many kinds of walls, including: * Walls in buildings that form a fundamental part of the su ...

) **

Gram negative