Symbiogenesis is the leading evolutionary theory of the origin of eukaryotic cells from prokaryotic organisms. The theory holds that mitochondria,plastids such as chloroplasts,and possibly other organelles of eukaryotic cells are descended from formerly free-living prokaryotes taken one inside the other in endosymbiosis. Mitochondria appear to be phylogenetically related to Rickettsiales bacteria,while chloroplasts are thought to be related to cyanobacteria.
Excavata is an extensive and diverse but possibly paraphyletic group of unicellular Eukaryota. The group was first suggested by Simpson and Patterson in 1999 and the name latinized and assigned a rank by Thomas Cavalier-Smith in 2002. It contains a variety of free-living and symbiotic protists,and includes some important parasites of humans such as Giardia and Trichomonas. Excavates were formerly considered to be included in the now obsolete Protista kingdom. They were distinguished from other lineages based on electron-microscopic information about how the cells are arranged. They are considered to be a basal flagellate lineage.
In biology,mating is the pairing of either opposite-sex or hermaphroditic organisms for the purposes of sexual reproduction. Fertilization is the fusion of two gametes. Copulation is the union of the sex organs of two sexually reproducing animals for insemination and subsequent internal fertilization. Mating may also lead to external fertilization,as seen in amphibians,fishes and plants. For most species,mating is between two individuals of opposite sexes. However,for some hermaphroditic species,copulation is not required because the parent organism is capable of self-fertilization (autogamy);for example,banana slugs.
Pelomyxa is a genus of giant flagellar amoebae,usually 500-800 μm but occasionally up to 5 mm in length,found in anaerobic or microaerobic bottom sediments of stagnant freshwater ponds or slow-moving streams.
Amorphea is a taxonomic supergroup that includes the basal Amoebozoa and Obazoa. That latter contains the Opisthokonta,which includes the Fungi,Animals and the Choanomonada,or Choanoflagellates. The taxonomic affinities of the members of this clade were originally described and proposed by Thomas Cavalier-Smith in 2002.
The retortamonads are a small group of flagellates,most commonly found in the intestines of animals as commensals,although a free-living species called the Chilomastix cuspidata exists. They are grouped under the taxon,Archezoa. They are usually around 5-20 μm in length,and all of their small subunit ribosomal RNA gene sequences are very similar to each other. There are two genera:Retortamonas with two flagella,and Chilomastix with four. In both cases there are four basal bodies anterior to a prominent feeding groove,and one flagellum is directed back through the cell,emerging from the groove.
Ancyromonas is a genus of basal Eukaryote consisting of heterotrophic flagellates.
Alphaproteobacteria is a class of bacteria in the phylum Pseudomonadota. The Magnetococcales and Mariprofundales are considered basal or sister to the Alphaproteobacteria. The Alphaproteobacteria are highly diverse and possess few commonalities,but nevertheless share a common ancestor. Like all Proteobacteria,its members are gram-negative and some of its intracellular parasitic members lack peptidoglycan and are consequently gram variable.
Breviata anathema is a single-celled flagellate amoeboid eukaryote,previously studied under the name Mastigamoeba invertens. The cell lacks mitochondria,but has remnant mitochondrial genes,and possesses an organelle believed to be a modified anaerobic mitochondrion,similar to the mitosomes and hydrogenosomes found in other eukaryotes that live in low-oxygen environments.
Malawimonas is genus of unicellular,heterotrophic flagellates with uncertain phylogenetic affinities. They have variably being assigned to Excavata and Loukozoa. Recent studies suggest they may be closely related to the Podiata.
Jakobids are an order of free-living,heterotrophic,flagellar eukaryotes in the supergroup Excavata. They are small,and can be found in aerobic and anaerobic environments. The order Jakobida,believed to be monophyletic,consists of only twenty species at present,and was classified as a group in 1993. There is ongoing research into the mitochondrial genomes of jakobids,which are unusually large and bacteria-like,evidence that jakobids may be important to the evolutionary history of eukaryotes.
Holozoa is a clade of organisms that includes animals and their closest single-celled relatives,but excludes fungi and all other organisms. Together they amount to more than 1.5 million species of purely heterotrophic organisms,including around 300 unicellular species. It consists of various subgroups,namely Metazoa and the protists Choanoflagellata,Filasterea,Pluriformea and Ichthyosporea. Along with fungi and some other groups,Holozoa is part of the Opisthokonta,a supergroup of eukaryotes. Choanofila was previously used as the name for a group similar in composition to Holozoa,but its usage is discouraged now because it excludes animals and is therefore paraphyletic.
Ancyromonadida or Planomonadida is a small group of biflagellated protists found in the soil and in aquatic habitats,where they feed on bacteria. Includes freshwater or marine organisms,benthic,dorsoventrally compressed and with two unequal flagellae,each emerging from a separate pocket. The apical anterior flagellum can be very thin or end in the cell membrane,while the posterior flagellum is long and is inserted ventrally or laterally. The cell membrane is supported by a thin single-layered theca and the mitochondrial crests are discoidal/flat.
The eukaryotes constitute the domain of Eukarya,organisms whose cells have a membrane-bound nucleus. All animals,plants,fungi,and many unicellular organisms are eukaryotes. They constitute a major group of life forms alongside the two groups of prokaryotes:the Bacteria and the Archaea. Eukaryotes represent a small minority of the number of organisms,but due to their generally much larger size,their collective global biomass is much larger than that of prokaryotes.
Picozoa,Picobiliphyta,Picobiliphytes,or Biliphytes are protists of a phylum of marine unicellular heterotrophic eukaryotes with a size of less than about 3 micrometers. They were formerly treated as eukaryotic algae and the smallest member of photosynthetic picoplankton before it was discovered they do not perform photosynthesis. The first species identified therein is Picomonas judraskeda. They probably belong in the Archaeplastida as sister of the Rhodophyta.
The Magnetococcales were an order of Alphaproteobacteria,but now the mitochondria are considered as sister to the alphaproteobactera,together forming the sister the marineproteo1 group,together forming the sister to Magnetococcidae.
Eukaryogenesis,the process which created the eukaryotic cell and lineage,is a milestone in the evolution of life,since eukaryotes include all complex cells and almost all multicellular organisms. The process is widely agreed to have involved symbiogenesis,in which archaea and bacteria came together to create the first eukaryotic common ancestor (FECA). This cell had a new level of complexity and capability,with a nucleus,at least one centriole and cilium,facultatively aerobic mitochondria,sex,a dormant cyst with a cell wall of chitin and/or cellulose and peroxisomes. It evolved into a population of single-celled organisms that included the last eukaryotic common ancestor (LECA),gaining capabilities along the way,though the sequence of the steps involved has been disputed,and may not have started with symbiogenesis. In turn,the LECA gave rise to the eukaryotes' crown group,containing the ancestors of animals,fungi,plants,and a diverse range of single-celled organisms.
Obazoa is a proposed sister clade of Amoebozoa. The term Obazoa is based on the OBA acronym for Opisthokonta,Breviatea,and Apusomonadida,the group's three constituent clades.
Anaeramoeba is a genus of anaerobic protists on uncertain phylogenetic position,first described in 2016.
A supergroup,in evolutionary biology,is a large group of organisms that share one common ancestor and have important defining characteristics. It is an informal,mostly arbitrary rank in biological taxonomy that is often greater than phylum or kingdom,although some supergroups are also treated as phyla.
