Excavata is a major supergroup of unicellular organisms belonging to the domain Eukaryota. It was first suggested by Simpson and Patterson in 1999 and introduced by Thomas Cavalier-Smith in 2002 as a formal taxon. It contains a variety of free-living and symbiotic forms, and also includes some important parasites of humans, including Giardia and Trichomonas. Excavates were formerly considered to be included in the now obsolete Protista kingdom. They are classified based on their flagellar structures, and they are considered to be the most basal Flagellate lineage. Phylogenomic analyses split the members of the Excavates into three different and not all closely related groups: Discobids, Metamonads and Malawimonads. Except for Euglenozoa, they are all non-photosynthetic.
The metamonads are microscopic eukaryotic organisms, a large group of flagellate amitochondriate Loukozoa. Their composition is not entirely settled, but they include the retortamonads, diplomonads, and possibly the parabasalids and oxymonads as well. These four groups are all anaerobic, occurring mostly as symbiotes or parasites of animals, as is the case with Giardia lamblia which causes diarrhea in mammals.
Amorphea are members of a taxonomic supergroup that includes the basal Amoebozoa and Obazoa. That latter contains the Opisthokonta, which includes the Fungi, Animals, the Choanomonada, or Choanoflagellates and Bacteria. The taxonomic affinities of the members of this clade were originally described and proposed by Thomas Cavalier-Smith in 2002.
The Apusozoa are an Obazoa phylum comprising several genera of flagellate eukaryotes. They are usually around 5–20 μm in size, and occur in soils and aquatic habitats, where they feed on bacteria. They are grouped together based on the presence of an organic shell or theca under the dorsal surface of the cell.
Corticata, in the classification of eukaryotes, is a clade suggested by Thomas Cavalier-Smith to encompass the eukaryote supergroups of the following two groups:
Malawimonadidae is a group of unicellular eukaryotes of outsize importance in understanding eukaryote phylogeny.
Micronuclearia is a genus of free-living protozoa. While originally thought to be a nucleariid, as reflected in the name, it is now inferred to be a member of the taxon Rigifilida, and to belong to the 'CRuMs' assemblage.
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.
Loukozoa is a proposed taxon used in some classifications of eukaryotes, consisting of the Metamonada and Malawimonadea. Ancyromonads are closely related to this group, as sister of the entire group, or as sister of the Metamonada. Amorphea may have emerged in this grouping, specifically as sister of the Malawimonads.
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 layer teak and the mitochondrial crests are discoidal / flat.
Diaphoretickes is a major group of eukaryotic creatures, with over 400,000 species. The majority of the earth's biomass that carries out photosynthesis belongs to Diaphoretickes.
Collodictyonidae is a group of aquatic, unicellular eukaryotic organisms with two to four terminal flagella. They feed by phagocytosis, ingesting other unicellular organisms like algae and bacteria. The most remarkable fact of this clade is its uncertain position in the tree of life.
Rigifila ramosa is one of the two members of the Rigifilida. It differs from the other member Micronuclearia podoventralis by having two pellicular layers covering the cell instead of a single one. Dorsal filopodia are also thicker and more conspicuous than in Micronuclearia.
Podiates are a proposed clade containing the Amorphea and the organisms now assigned to the clade CRuMs. Ancyromonadida does not appear to have emerged in this grouping. Sarcomastigota is a proposed subkingdom that includes all the podiates that are not animals or fungi. Sulcozoa is a proposed phylum within Sarcomastigota that does not include the phyla Amoebozoa (clade) and Choanozoa (paraphyletic), i.e. it includes the proposed subphyla Apusozoa and Varisulca
Endohelea is a proposed clade of eukaryotes that are related to Archaeplastida and the SAR supergroup.
Obazoa is a proposed sister clade of Amoebozoa. Obazoa is composed of Breviatea, Apusomonadida and Opisthokonta. The term Obazoa is based on the OBA acronym for Opisthokonta, Breviatea, and Apusomonadida.
The Orthokaryotes are a proposed Eukaryote clade consisting of the Jakobea and the Neokaryotes. Together with its sister Discicristata it forms a basal Eukaryote clade. They are characterized by stacked Golgi, orthogonal centrioles, and two opposite posterior ciliary roots.
The neokaryotes are a proposed eukaryote clade consisting of the unikonts and the bikonts as sister of for instance the Jakobea. It arises because the Euglenozoa, Percolozoa, Tsukubea, and Jakobea are seen in this view as more basal eukaryotes. These four groups, are traditionally grouped together in the Discoba. However, the Discoba may well be paraphyletic as the neokaryotes may have emerged in them.
The Scotokaryotes (Cavalier-Smith) is a proposed basal Neokaryote clade as sister of the Diaphoretickes. Basal Scotokaryote groupings are the Metamonads, the Malawimonas and the Podiata. In this phylogeny the Discoba are sometimes seen as paraphyletic and basal Eukaryotes.
The Mantamonadidae are of free-living heterotrophic flagellates that move primarily by gliding on surfaces. There is one genus, Mantamonas. It has been suggested previously that the Mantamonadidae be classified in Apusozoa as sister of the Apusmonadida on the basis of rRNA analyses. However, mantamonads are currently placed in CRuMs on the basis of phylogenomic analyses that identify their closest relatives as the collodictyonids (=diphylleids) and Rigifila.
