excavate
American Heritage Dictionary:
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ex·ca·vate
(ĕk'skə-vāt') 
v., -vat·ed, -vat·ing, -vates. v.tr.
To engage in digging, hollowing out, or removing.
v., -vat·ed, -vat·ing, -vates. v.tr.
- To make a hole in; hollow out: excavate an ore-rich hillside.
- To form by hollowing out.
- To remove by digging or scooping out.
- To expose or uncover by or as if by digging: excavate an archaeological site.
To engage in digging, hollowing out, or removing.
[Latin excavāre, excavāt-, to hollow out : ex-, ex- + cavāre, to hollow (from cavus, hollow).]
Roget's Thesaurus:
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excavate
Word Tutor:
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excavate
IN BRIEF: To remove by digging or scooping out.
The backhoe will excavate the ditches for the water pipes.
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Excavate
This article is about the protist group. For the process of digging, see Excavation (disambiguation).
| Excavates | |
|---|---|
 |
|
| Giardia lamblia, a parasitic diplomonad | |
Scientific classification  |
|
| Domain: | Eukaryota |
| (unranked): | Bikonta |
| Kingdom: | Excavata (Cavalier-Smith) Simpson, 2003 |
| Phyla | |
The excavates are a major kingdom of unicellular[1] eukaryotes,[2] often known as Excavata. The phylogenetic category Excavata, proposed by Cavalier-Smith in 2002, contains a variety of free-living and symbiotic forms, and also includes some important parasites of humans.
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Contents
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Characteristics
Many excavates lack 'classical' mitochondria - these organisms are often referred to as 'amitochondriate', although most, perhaps all, retain a mitochondrial organelle in greatly modified form. Others have mitochondria with tubular, discoidal, or in some cases, laminar cristae. Most excavates have two, four, or more flagella[3] and many have a conspicuous ventral feeding groove with a characteristic ultrastructure, supported by microtubules.[4] However, various groups that lack these traits may be considered excavates based on genetic evidence (primarily phylogenetic trees of molecular sequences).
The closest that the excavates come to multicellularity are the Acrasidae slime molds. Like other cellular slime molds, they live most of their life as single cells, but will sometimes assemble into a larger cluster.
Subgroups
See also: Eukaryote#Phylogeny
Excavates are classified into six major subgroups at the phylum/class level. These are shown in the table below.
| Superphylum | Phylum/Class | Representative genera | Description |
|---|---|---|---|
| Discoba or JEH | Euglenozoa | e.g. Euglena, Trypanosoma | Many important parasites, one large group with plastids (chloroplasts) |
| Heterolobosea (Percolozoa) | e.g. Naegleria, Acrasis | Most alternate between flagellate and amoeboid forms | |
| Jakobea | e.g. Jakoba, Reclinomonas | Free-living, sometimes loricate flagellates, with very gene-rich mitochondrial genomes | |
| Metamonada or POD | Preaxostyla | e.g. Oxymonads, Trimastix | Amitochondriate flagellates, either free-living (Trimastix) or living in the hindguts of insects |
| Fornicata | e.g. Giardia, Carpediemonas | Amitochondriate, mostly symbiotes and parasites of animals. | |
| Parabasalia | e.g. Trichomonas | Amitochondriate flagellates, generally intestinal commensals of insects. Some human pathogens. |
Discoba or JEH clade
Euglenozoa and Heterolobosea (Percolozoa) appear to be particularly close relatives, and are united by the presence of discoid cristae within the mitochondria (Superphylum Discicristata). More recently a close relationship has been shown between Discicristata and Jakobida,[5] the latter having tubular cristae like most other protists, and hence were united under the taxon name Discoba which was proposed for this apparently monophyletic group.[2]
Metamonads
Metamonads are unusual in having lost classical mitochondria—instead they have hydrogenosomes, mitosomes or uncharacterised organelles.
Monophyly
Excavate relationships are still uncertain; it is possible that they are not a monophyletic group. The monophyly of the excavates is far from clear, although it seems like there are several clades within the excavates which are monophyletic.[6]
Certain excavates are often considered among the most primitive eukaryotes, based partly on their placement in many evolutionary trees. This could encourage proposals that excavates are a paraphyletic grade that includes the ancestors of other living eukaryotes. However, the placement of certain excavates as 'early branches' may be an analysis artifact caused by long branch attraction, as has been seen with some other groups, for example, microsporidia.
Malawimonas
In addition to the groups mentioned in the table above, the genus Malawimonas is generally considered to be a member of Excavata owing to its typical excavate morphology, and phylogenetic affinity to excavate groups in some molecular phylogenies. However, its position among excavates remains elusive[citation needed].
References
- ^ Simpson, Ag; Inagaki, Y; Roger, Aj (Mar 2006). "Comprehensive multigene phylogenies of excavate protists reveal the evolutionary positions of "primitive" eukaryotes" (Free full text). Molecular Biology and Evolution 23 (3): 615–25. doi:10.1093/molbev/msj068. PMID 16308337. http://mbe.oxfordjournals.org/cgi/pmidlookup?view=long&pmid=16308337
- ^ a b Hampl V, Hug L, Leigh JW, et al (March 2009). "Phylogenomic analyses support the monophyly of Excavata and resolve relationships among eukaryotic "supergroups"". Proc. Natl. Acad. Sci. U.S.A. 106 (10): 3859–64. Bibcode 2009PNAS..106.3859H. doi:10.1073/pnas.0807880106. PMC 2656170. PMID 19237557. http://www.pnas.org/cgi/pmidlookup?view=long&pmid=19237557.
- ^ Simpson AG (November 2003). "Cytoskeletal organization, phylogenetic affinities and systematics in the contentious taxon Excavata (Eukaryota)". Int. J. Syst. Evol. Microbiol. 53 (Pt 6): 1759–77. doi:10.1099/ijs.0.02578-0. PMID 14657103. http://ijs.sgmjournals.org/cgi/pmidlookup?view=long&pmid=14657103.
- ^ Cavalier-Smith T (March 2002). "The phagotrophic origin of eukaryotes and phylogenetic classification of Protozoa". Int. J. Syst. Evol. Microbiol. 52 (Pt 2): 297–354. PMID 11931142. http://ijs.sgmjournals.org/cgi/pmidlookup?view=long&pmid=11931142.
- ^ Naiara Rodríguez-Ezpeleta, Henner Brinkmann, Gertraud Burger, Andrew J. Roger, Michael W. Gray, Hervé Philippe, and B. Franz Lang (August 2007). "Toward Resolving the Eukaryotic Tree: The Phylogenetic Positions of Jakobids and Cercozoans". Curr. Biol. 17 (16): 1420–1425. doi:10.1016/j.cub.2007.07.036. PMID 17689961. http://www.cell.com/current-biology/retrieve/pii/S0960982207017162.
- ^ Laura Wegener Parfrey, Erika Barbero, Elyse Lasser, Micah Dunthorn, Debashish Bhattacharya, David J Patterson, and Laura A Katz (December 2006). "Evaluating Support for the Current Classification of Eukaryotic Diversity". PLoS Genet. 2 (12): e220. doi:10.1371/journal.pgen.0020220. PMC 1713255. PMID 17194223. http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=1713255.
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This entry is from Wikipedia, the leading user-contributed encyclopedia. It may not have been reviewed by professional editors (see full disclaimer)
Translations:
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Excavate
Dansk (Danish)
v. tr. - grave, grave op, grave væk, udgrave
v. intr. - udgrave, opgrave
Nederlands (Dutch)
uithollen, graven, opdelven, opgraven
Français (French)
v. tr. - fouiller, creuser, excaver, (Archéol) fouiller, creuser (une tranchée), dégager, déterrer (des restes)
v. intr. - (Archéol) faire des fouilles
Deutsch (German)
v. - ausschachten, ausbaggern, ausgraben
Ελληνική (Greek)
v. - ανασκάπτω, κάνω ανασκαφές, σκάπτω, ανοίγω, εκβαθύνω, βαθαίνω
Português (Portuguese)
v. - escavar, desenterrar
Русский (Russian)
выкопать, раскапывать, производить раскопки
Español (Spanish)
v. tr. - excavar, cavar, desenterrar
v. intr. - excavar, cavar, desenterrar
Svenska (Swedish)
v. - gräva, gräva ut, gräva upp
中文（简体）(Chinese (Simplified))
挖掘, 发掘, 开凿
中文（繁體）(Chinese (Traditional))
v. tr. - 挖掘, 發掘, 開鑿
v. intr. - 挖掘, 發掘
한국어 (Korean)
v. tr. - 파다
v. intr. - 구멍을 파다, 발굴하다
日本語 (Japanese)
v. - 穴を掘る, 掘り出す, 発掘する, 掘り抜く
العربيه (Arabic)
(فعل) ينقب عن الآثار
עברית (Hebrew)
v. tr. - חפר, גילה עתיקות
v. intr. - חפר, כרה
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