The excavates are a major line of protists, often known as Excavata. The phylogenetic category Excavata includes a variety of free-living and symbiotic forms, as well as microbes varying as to whether they contain mitochondria (that is, amitochondriate versus discicristate). Excavates are usually characterized by having two, four, or more flagella with distinct ultrastructure anterior to a ventral feeding groove supported by microtubules. However, various groups that lack these traits may be considered excavates based on genetic evidence. Most excavates fall into four groups, which may be treated as phyla: Typical phyla Rhodophyta (red algae) Chromista Heterokontophyta (heterokonts) Haptophyta Cryptophyta (cryptomonads) Alveolates Dinoflagellata Apicomplexa Ciliophora (ciliates) Excavates Euglenozoa Percolozoa Metamonada Rhizaria Radiolaria Foraminifera Cercozoa Amoebozoa Choanozoa Many others; classification varies Protists (IPA: [prəʊˌtɪst]) are a heterogeneous group of living things, comprising those eukaryotes that are neither animals, plants... A flagellum (plural, flagella) is a whip-like organelle that many unicellular organisms, and some multicellular ones, use to move about. ... Ultrastructure is the detailed structure of a biological specimen, such as a cell, tissue, or organ, that can be by electron microscopy. ... Microtubules are protein structures found within cells, one of the components of the cytoskeleton. ...

Of these, the Percolozoa and Euglenozoa appear to be particularly close relatives, and are united by the presence of discoid cristae within the mitochondria. The jakobids have tubular cristae, like most other protists, while the metamonads are unusual in having lost their mitochondria. Excavate relationships are still uncertain; it is possible that they are not monophyletic groups. Classes & orders Eopharyngia    Retortamonadida    Diplomonadida    Carpediemonas Parabasalia Anaeromonada    Oxymonadida    Trimastix The metamonads are a group of flagellate protozoa, including the retortamonads, diplomonads, and possibly the parabasalids and oxymonads as well. ... Binomial name Giardia lamblia (Kunstler, 1882) Giardia lamblia (formerly also Lamblia intestinalis) is a protozoan parasite that infects the gastrointestinal tract of humans. ... Binomial name Trichomonas vaginalis (Donné, 1836) Trichomonas vaginalis is an anaerobic and occasionally parasitic protozoan that is frequently present in the vagina in women and the urethra in men. ... The Percolozoa are a group of colorless protists including many that can transform between amoeboid, flagellate, and encysted stages, collectively referred to as schizopyrenids or amoeboflagellates. ... Naegleria fowleri is a free living, pathogenic amoeba typically found in warm fresh water, from 25-35 degrees Celsius. ... Classes Euglenoidea Kinetoplastea Diplonemea Postgaardea The Euglenozoa are a large group of flagellate protozoa, dominated by the euglenids and kinetoplastids. ... Euglena is a common genus of flagellate protozoa, typical of the euglenids, and commonly found in nutrient-rich freshwater, with a few marine species. ... Trypanosoma is a notable genus of trypanosomes, a group of parasitic protozoa. ... Cross-section of a mitochondrion, showing: (1) inner membrane, (2) outer membrane, (3) cristae, (4) matrix Cristae are the infoldings of the inner membrane of a mitochondrion. ... This article contains material from the Science Primer published by the NCBI, which, as a US government publication, is in the public domain at http://www. ... In phylogenetics, a group is monophyletic (Greek: of one stem) if all organisms in that group are known to have developed from a common ancestral form, and all descendants of that form are included in the group. ...

The excavates are often considered among the most primitive eukaryotes, and may be paraphyletic to the others. However, this placement may be an artifact caused by long branch attraction, as has been seen with some other amitochondriate groups, and in some phylogenies the excavates show up as an advanced group. Kingdoms Animalia - Animals Fungi Plantae - Plants Protista A eukaryote (also spelled eucaryote) is an organism with complex cells, in which the genetic material is organized into membrane-bound nuclei. ... Paraphyletic - Wikipedia /**/ @import /skins-1. ... Long branch attraction (LBA) is a phenomenon in phylogenetic analyses (most commonly those employing maximum parsimony) when rapidly evolving lineages are inferred to be closely related, regardless of their true evolutionary relationships. ...

References

• Cavalier-Smith, T. (2002). "The phagotrophic origin of eukaryotes and phylogenetic classification of Protozoa". International Journal of Systematic and Evolutionary Microbiology 52: 297-354.
• Alastair G. B. Simpson (2003). "Cytoskeletal organization, phylogenetic affinities and systematics in the contentious taxon Excavata". International Journal of Systematic and Evolutionary Microbiology 53: 1759-1777.