Chordate
| Chordates | |
|---|---|
  | |
| Example of chordates: Branchiostoma lanceolatum (Cephalochordata), Polycarpa aurata (Tunicata), as well as a Tiger shark and a Siberian tiger (Vertebrata). | |
Scientific classification 
| |
| Kingdom: | Animalia |
| Subkingdom: | Eumetazoa |
| Clade: | ParaHoxozoa |
| Clade: | Bilateria |
| Clade: | Nephrozoa |
| Superphylum: | Deuterostomia |
| Phylum: | Chordata Haeckel, 1874[3][4] |
| Subgroups | |
And see text | |
A chordate (
In addition to the morphological characteristics used to define chordates, analysis of genome sequences has identified two
Chordates are divided into three
Chordate
Anatomy
Chordates form a phylum of animals that are defined by having at some stage in their lives all of the following anatomical features:[8]
- A notochord, a stiff rod of cartilage that extends along the inside of the body. Among the vertebrate sub-group of chordates the notochord develops into the spine, and in wholly aquatic species this helps the animal to swim by flexing its tail.
- A dorsal neural tube. In fish and other vertebrates, this develops into the spinal cord, the main communications trunk of the nervous system.
- filter-feeding system that extracts particles of food from the water in which the animals live. In tetrapods, they are only present during embryonic stages of the development.
- Post-anal tail. A muscular tail that extends backwards behind the anus. In some chordates such as humans, this is only present in the embryonic stage.
- An
There are soft constraints that separate chordates from other biological lineages, but are not part of the formal definition:
- All chordates are deuterostomes. This means that, during the embryo development stage, the anus forms before the mouth.
- All chordates are based on a
- All chordates are coelomates, and have a fluid-filled body cavity called a coelom with a complete lining called peritoneum derived from mesoderm (see Brusca and Brusca).[11]
Classification
The following schema is from the 2015 edition of
- Phylum Chordata
- Subphylum Cephalochordata(Acraniata) – (lancelets; 30 species)
- Class Leptocardii(lancelets)
- Class
- Clade Olfactores
- Subphylum Tunicata(Urochordata) – (tunicates; 3,000 species)
- Class Ascidiacea (sea squirts)
- Class Thaliacea (salps)
- Class Appendicularia(larvaceans)
- Class Sorberacea
- Subphylum Craniata) (vertebrates – animals with backbones; 66,100+ species)
- Superclass 'paraphyletic(jawless vertebrates; 100+ species)
- Class Cyclostomata
- Infraclass Myxini(hagfish; 65 species)
- Infraclass Petromyzontida or Hyperoartia(lampreys)
- Infraclass
- Class †Conodonta
- Class †Myllokunmingiida
- Class †Pteraspidomorphi
- Class †Thelodonti
- Class †Anaspida
- Class †Cephalaspidomorphi
- Class
- Infraphylum Gnathostomata (jawed vertebrates)
- Class †Placodermi (Paleozoic armoured forms; paraphyletic in relation to all other gnathostomes)
- Class Chondrichthyes (cartilaginous fish; 900+ species)
- Class †Acanthodii (Paleozoic "spiny sharks"; paraphyletic in relation to Chondrichthyes)
- Class Osteichthyes (bony fish; 30,000+ species)
- Subclass Actinopterygii (ray-finned fish; about 30,000 species)
- Subclass Sarcopterygii (lobe-finned fish: 8 species)
- Superclass Tetrapoda (four-limbed vertebrates; 35,100+ species) (The classification below follows Benton 2004, and uses a synthesis of rank-based Linnaean taxonomy and also reflects evolutionary relationships. Benton included the Superclass Tetrapoda in the Subclass Sarcopterygii in order to reflect the direct descent of tetrapods from lobe-finned fish, despite the former being assigned a higher taxonomic rank.)[15]
- Superclass '
- Subphylum
- Subphylum
Subphyla
Cephalochordata: Lancelets
Cephalochordates, one of the three subdivisions of chordates, are small, "vaguely fish-shaped" animals that lack brains, clearly defined heads and specialized sense organs.[20] These burrowing filter-feeders compose the earliest-branching chordate sub-phylum.[21][22]
Tunicata (Urochordata)
Most
Craniata (Vertebrata)
Craniates all have distinct skulls. They include the hagfish, which have no vertebrae. Michael J. Benton commented that "craniates are characterized by their heads, just as chordates, or possibly all deuterostomes, are by their tails".[27]
Most craniates are
The position of
Phylogeny
Overview
There is still much ongoing differential (DNA sequence based) comparison research that is trying to separate out the simplest forms of chordates. As some lineages of the 90% of species that lack a backbone or notochord might have lost these structures over time, this complicates the classification of chordates. Some chordate lineages may only be found by DNA analysis, when there is no physical trace of any chordate-like structures.[36]
Attempts to work out the evolutionary relationships of the chordates have produced several hypotheses. The current consensus is that chordates are
All of the earliest chordate
It has also proved difficult to produce a detailed classification within the living chordates. Attempts to produce evolutionary "
| Deuterostomes |
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While this has been well known since the 19th century, an insistence on only monophyletic taxa has resulted in vertebrate classification being in a state of flux.[37]
The majority of animals more complex than
, the world's fastest animal. Peregrines use gravity and aerodynamics to achieve their top speed of around 242mph (389km/h), as opposed to locomotion.Fossils of one major deuterostome group, the
The evolutionary relationships between the chordate groups and between chordates as a whole and their closest deuterostome relatives have been debated since 1890. Studies based on anatomical, embryological, and paleontological data have produced different "family trees". Some closely linked chordates and hemichordates, but that idea is now rejected.[9] Combining such analyses with data from a small set of ribosome RNA genes eliminated some older ideas, but opened up the possibility that tunicates (urochordates) are "basal deuterostomes", surviving members of the group from which echinoderms, hemichordates and chordates evolved.[49] Some researchers believe that, within the chordates, craniates are most closely related to cephalochordates, but there are also reasons for regarding tunicates (urochordates) as craniates' closest relatives.[9][50]
Since early chordates have left a poor fossil record, attempts have been made to calculate the key dates in their evolution by molecular phylogenetics techniques—by analyzing biochemical differences, mainly in RNA. One such study suggested that deuterostomes arose before 900 million years ago and the earliest chordates around 896 million years ago.[50] However, molecular estimates of dates often disagree with each other and with the fossil record,[50] and their assumption that the molecular clock runs at a known constant rate has been challenged.[51][52]
Traditionally, Cephalochordata and Craniata were grouped into the proposed clade "Euchordata", which would have been the sister group to Tunicata/Urochordata. More recently, Cephalochordata has been thought of as a sister group to the "Olfactores", which includes the craniates and tunicates. The matter is not yet settled.
A specific relationship between Vertebrates and Tunicates is also strongly supported by two CSIs found in the proteins predicted exosome complex RRP44 and serine palmitoyltransferase, that are exclusively shared by species from these two subphyla but not Cephalochordates, indicating Vertebrates are more closely related to Tunicates than Cephalochordates.[5]
Cladogram
| Chordata |
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Closest nonchordate relatives
The closest relatives of the Chordates are the
Hemichordates
There are two living groups of hemichordates. The solitary
Echinoderms
History of name
Although the name Chordata is attributed to William Bateson (1885), it was already in prevalent use by 1880. Ernst Haeckel described a taxon comprising tunicates, cephalochordates, and vertebrates in 1866. Though he used the German vernacular form, it is allowed under the ICZN code because of its subsequent latinization.[4]
See also
- Chordate genomics
- List of chordate orders – All the classes and orders of phylum Chordata
References
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- ^ Haeckel, E. (1874). Anthropogenie oder Entwicklungsgeschichte des Menschen. Leipzig: Engelmann.
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- ^ "Stratigraphic Chart 2022" (PDF). International Stratigraphic Commission. February 2022. Archived (PDF) from the original on 9 October 2022. Retrieved 25 April 2022.
- ^ "Chordates". eol.
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- ^ doi:10.1139/Z04-158. Archived from the originalon 9 December 2012. Retrieved 22 September 2008.
- ISBN 978-0-226-84548-7.
- ISBN 0-87893-097-3.
- ^ Benton, M.J. (2004). Vertebrate Palaeontology, Third Edition. Blackwell Publishing. The classification scheme is available online Archived 19 October 2008 at the Wayback Machine
- ISBN 978-1-118-40764-6.
- ISBN 978-0-471-25031-9.
- ^ Benton, M.J. (2004). Vertebrate Paleontology. 3rd ed. Blackwell Science Ltd.
- Frost, Darrel R. "ASW Home". Amphibian Species of the World, an Online Reference. Version 6.0. American Museum of Natural History, New York. Retrieved 11 November 2019.
- ^ "Reptiles face risk of extinction". 15 February 2013. Archived from the original on 17 September 2018. Retrieved 20 December 2019 – via www.bbc.co.uk.
- ^ "New Study Doubles the Estimate of Bird Species in the World". Amnh.org. Retrieved 15 October 2018.
- ^ "Species Statistics Aug 2019". www.reptile-database.org.
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- ^ "Branchiostoma". Lander University. Retrieved 5 February 2016.
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- ^ "Animal fact files: salp". BBC. Archived from the original on 21 June 2013. Retrieved 22 September 2008.
- ^ "Appendicularia" (PDF). Australian Government Department of the Environment, Water, Heritage and the Arts. Archived from the original (PDF) on 20 March 2011. Retrieved 28 October 2008.
- ^ Oxford English Dictionary, Third Edition, January 2009: Urochordata
- ISBN 978-0-632-05614-9. Retrieved 22 September 2008.
- ^ "Morphology of the Vertebrates". University of California Museum of Paleontology. Retrieved 23 September 2008.
- ^ "Introduction to the Myxini". University of California Museum of Paleontology. Archived from the original on 15 December 2017. Retrieved 28 October 2008.
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{{cite book}}: CS1 maint: multiple names: authors list (link - PMID 21041649.
Although I was among the early supporters of vertebrate paraphyly, I am impressed by the evidence provided by Heimberg et al. and prepared to admit that cyclostomes are, in fact, monophyletic. The consequence is that they may tell us little, if anything, about the dawn of vertebrate evolution, except that the intuitions of 19th century zoologists were correct in assuming that these odd vertebrates (notably, hagfishes) are strongly degenerate and have lost many characters over time
- ^ "Introduction to the Petromyzontiformes". University of California Museum of Paleontology. Archived from the original on 24 January 2018. Retrieved 28 October 2008.
- S2CID 5613153.
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Delabre, Christiane; et al. (2002). "Complete Mitochondrial DNA of the Hagfish, Eptatretus burgeri: The Comparative Analysis of Mitochondrial DNA Sequences Strongly Supports the Cyclostome Monophyly". Molecular Phylogenetics and Evolution. 22 (2): 184–192. PMID 11820840.
- ^ S2CID 4401274.
- ^ Josh Gabbatiss (15 August 2016), Why we have a spine when over 90% of animals don't, BBC
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- doi:10.1111/j.1502-3931.1986.tb00743.x. Archived from the originalon 16 December 2012.
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External links
- "Chordate" at the Encyclopedia of Life
- Chordate on GlobalTwitcher.com
- Chordate node at Tree Of Life
- Chordate node at NCBI Taxonomy
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