Difference between revisions of "Chordate" - New World Encyclopedia
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* Subphylum [[Vertebrate|Vertebrata]] - [[Vertebrate]]s | * Subphylum [[Vertebrate|Vertebrata]] - [[Vertebrate]]s | ||
** [[Myxini]] | ** [[Myxini]] | ||
| − | ** [[Conodonta]] | + | ** [[Conodonta]]* |
** [[Hyperoartia]]* | ** [[Hyperoartia]]* | ||
** [[Cephalaspidomorphi]]* | ** [[Cephalaspidomorphi]]* | ||
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** [[Mammal]]ia | ** [[Mammal]]ia | ||
{{Taxobox_end}} | {{Taxobox_end}} | ||
| − | '''Chordates''' (phylum '''Chordata''') are a group of [[animal]]s that includes all the [[vertebrate]]s (subphylum Vertebrata), as well as two | + | '''Chordates''' (phylum '''Chordata''') are a group of [[animal]]s that includes all the [[vertebrate]]s (subphylum Vertebrata), as well as two subphylum of [[invertebrate]]s, the [[Urochordata]] (tunicates) and the [[Cephalochordata]] (lancelets). |
| − | The distinguishing features of | + | The distinguishing features of the Chordata phylum is that they all have, at some time in their life, a ''notochord'', a hollow ''dorsal nerve cord'', and ''pharyngeal slits''. A notochord is an internal, flexible rod that supports the body. Composed of [[cell (biology)|cell]]s derived from the mesoderm, the notochord may be bone or cartilage. In lower vertebrates, it persists throughout life as the main axial support of the body, while in higher vertebrates it is replaced by the vertebral column. Pharyngeal slits are vertical slits in the wall of the pharynx, which is used in primative chordates to strain water and filter out food particles, but appear in most terrestrial vertebrates only in the embryonic stage. |
| − | == | + | ==Types of chordates== |
| − | + | Chordata is a phylum and is broken down into three subphyla: [[Urochordata]], [[Cephalochordata]], and [[Vertebrata]]. Urochordate larvae have a notochord and a nerve cord but they are lost in adulthood. Cephalochordates have a notochord and a nerve cord but no vertebra. In all vertebrates, except for [[Hagfish]], the dorsal hollow nerve cord has been surrounded with cartilaginous or bony vertebrae and the notochord generally reduced. Unlike vertebrates, tunicates and cephalochordates lack any kind of skulls. (Those with skulls, that is the vertebrtes, are placed in the taxonomic group Craniata.) | |
| − | The chordates and two sister phyla, the [[hemichordate]]s and the [[echinoderm]]s, make up the | + | The chordates and two sister phyla, the [[hemichordate]]s and the [[echinoderm]]s, make up the deuterostomes, a superphylum. |
| − | + | ===Classes of chordates=== | |
| + | In the subphylum [[Tunicata|Urochordata]], classes [[Ascidiacea]], [[Thaliacea]], [[Larvacea]] are found. Included are the [[sea squirt]]s and [[tunicate]]s. | ||
| − | + | In the subphylum [[Lancelet|Cephalochordata]], the worm-like lancelets are found. | |
| − | + | In the subphylum [[Vertebrate|Vertebrata]] (all animals with vertebrae) the following classes are often recognized: [[Myxini]] (hagfish), Conodonta, [[Hyperoartia]] (lampreys), Cephalaspidomorphi, Pteraspidomorphi, Placodermi, [[Chondrichthyes]] (sharks, rays and skates), Acanthodii (spiny sharks), [[Actinopterygii]] (ray-finned fish), [[Sarcopterygii]] (lobe-finned fish), [[Amphibia]] (amphibians), [[Sauropsida]] (reptiles), [[Synapsida]], [[Aves]] (birds), and [[Mammal]]ia (mammals). | |
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| − | + | ===Taxonomy=== | |
| − | + | The extant groups of chordates are related as shown in the phylogenetic tree below. Many of the taxa listed do not match traditional classes because several of those classes are paraphyletic. Different attempts to organize the profusion of chordate clades into a small number of groups, some with and some without paraphyletic taxa, have thrown vertebrate classification is in a state of flux. Also, the relationships of some chordate groups are not very well understood. | |
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| − | + | *'''Phylum Chordata''' | |
| − | + | ** Subphylum '''[[Urochordata]]''' - [[Tunicata|Tunicate]]s | |
| − | + | ** Subphylum '''[[Cephalochordata]]''' - [[Lancelet]]s | |
| − | + | ** Class '''[[Myxini]]''' or [[Hyperotreti]] ([[hagfish]]) | |
| − | + | ** Subphylum '''[[Vertebrata]]''' ([[Vertebrate]]s - animals with backbones) | |
| − | + | *** Class '''Conodonta''' (Conodonts) | |
| − | + | *** Class '''Cephalaspidomorphi''' (jawless fish) | |
| − | :: | + | *** Class '''Pteraspidomorphi''' (Paleozoic jawless fish) |
| + | *** Infraphylum '''Gnathostomata''' ([[jaw]]ed vertebrates) | ||
| + | **** Class '''Placodermi''' (Paleozoic armored forms) | ||
| + | **** Class '''[[Chondrichthyes]]''' (cartilaginous fish) | ||
| + | **** Class '''Acanthodii''' (Paleozoic "spiny sharks") | ||
| + | **** Superclass '''[[Osteichthyes]]''' (bony fishes) | ||
| + | ***** Class '''[[Actinopterygii]]''' (ray-finned fish) | ||
| + | ***** Class '''[[Sarcopterygii]]''' (lobe-finned fish) | ||
| + | ***** Superclass '''Tetrapoda''' (four-legged vertebrates) | ||
| + | ****** Class '''[[Amphibia]]''' (amphibians) | ||
| + | ****** Series '''Amniota''' (amniotic egg) | ||
| + | ******* Class '''[[Synapsida]]''' (mammal-like "reptiles") | ||
| + | ******* Class '''[[Mammal]]ia''' (mammals) | ||
| + | ******* Class '''[[Sauropsida]]''' - ([[reptile]]s) | ||
| + | ******* Class '''[[Bird|Aves]]''' (birds) | ||
| + | |||
| + | ===Phylogeny=== | ||
| + | <code style="border:0px; background:none"> | ||
| + | '''Chordata''' | ||
| + | ├─'''[[Urochordata]]''' ([[Tunicata|tunicates]]) | ||
| + | ├─'''[[Cephalochordata]]''' ([[lancelet]]s) | ||
| + | └'''Craniata''' (animals with skulls) | ||
| + | ├─'''[[Myxini]]''' or Hyperotreti ([[hagfish]]) | ||
| + | └'''[[Vertebrata]]''' (animals with backbones) | ||
| + | ├─'''Conodonta''' (Conodonts) | ||
| + | ├─'''Cephalaspidomorphi''' (Paleozoic jawless fish) | ||
| + | ├─'''Hyperoartia''' ([[lamprey]]s and kin) | ||
| + | ├─'''Pteraspidomorphi''' (other Paleozoic jawless fish) | ||
| + | └'''Gnathostomata''' (jawed vertebrates) | ||
| + | ├─'''Placodermi''' (Paleozoic armored forms) | ||
| + | ├─'''[[Chondrichthyes]]''' (cartilaginous fish) | ||
| + | └'''Teleostomi''' (advanced fishes and their descendants) | ||
| + | ├─'''Acanthodii''' (Paleozoic "spiny sharks") | ||
| + | └─'''[[Osteichthyes]]''' (bony fishes) | ||
| + | ├─'''[[Actinopterygii]]''' (ray-finned fish) | ||
| + | └─'''[[Sarcopterygii]]''' (lobe-finned fish) | ||
| + | └'''Tetrapoda''' (four-legged vertebrates) | ||
| + | ├─'''[[Lissamphibia]]''' (frogs and kin) | ||
| + | └'''[[Amniota]]''' (amniotic egg) | ||
| + | ├'''[[Synapsida]]''' (mammals and kin) | ||
| + | └'''[[Sauropsida]]''' ([[reptile]]s and birds) | ||
| + | |||
| + | Note: Lines show probable evolutionary relationships (including extinct members of taxa) | ||
| + | </code> | ||
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Revision as of 22:41, 26 November 2006
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 Yellowfin tuna, Thunnus albacares | ||||||||
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Chordates (phylum Chordata) are a group of animals that includes all the vertebrates (subphylum Vertebrata), as well as two subphylum of invertebrates, the Urochordata (tunicates) and the Cephalochordata (lancelets).
The distinguishing features of the Chordata phylum is that they all have, at some time in their life, a notochord, a hollow dorsal nerve cord, and pharyngeal slits. A notochord is an internal, flexible rod that supports the body. Composed of cells derived from the mesoderm, the notochord may be bone or cartilage. In lower vertebrates, it persists throughout life as the main axial support of the body, while in higher vertebrates it is replaced by the vertebral column. Pharyngeal slits are vertical slits in the wall of the pharynx, which is used in primative chordates to strain water and filter out food particles, but appear in most terrestrial vertebrates only in the embryonic stage.
Types of chordates
Chordata is a phylum and is broken down into three subphyla: Urochordata, Cephalochordata, and Vertebrata. Urochordate larvae have a notochord and a nerve cord but they are lost in adulthood. Cephalochordates have a notochord and a nerve cord but no vertebra. In all vertebrates, except for Hagfish, the dorsal hollow nerve cord has been surrounded with cartilaginous or bony vertebrae and the notochord generally reduced. Unlike vertebrates, tunicates and cephalochordates lack any kind of skulls. (Those with skulls, that is the vertebrtes, are placed in the taxonomic group Craniata.)
The chordates and two sister phyla, the hemichordates and the echinoderms, make up the deuterostomes, a superphylum.
Classes of chordates
In the subphylum Urochordata, classes Ascidiacea, Thaliacea, Larvacea are found. Included are the sea squirts and tunicates.
In the subphylum Cephalochordata, the worm-like lancelets are found.
In the subphylum Vertebrata (all animals with vertebrae) the following classes are often recognized: Myxini (hagfish), Conodonta, Hyperoartia (lampreys), Cephalaspidomorphi, Pteraspidomorphi, Placodermi, Chondrichthyes (sharks, rays and skates), Acanthodii (spiny sharks), Actinopterygii (ray-finned fish), Sarcopterygii (lobe-finned fish), Amphibia (amphibians), Sauropsida (reptiles), Synapsida, Aves (birds), and Mammalia (mammals).
Taxonomy
The extant groups of chordates are related as shown in the phylogenetic tree below. Many of the taxa listed do not match traditional classes because several of those classes are paraphyletic. Different attempts to organize the profusion of chordate clades into a small number of groups, some with and some without paraphyletic taxa, have thrown vertebrate classification is in a state of flux. Also, the relationships of some chordate groups are not very well understood.
- Phylum Chordata
- Subphylum Urochordata - Tunicates
- Subphylum Cephalochordata - Lancelets
- Class Myxini or Hyperotreti (hagfish)
- Subphylum Vertebrata (Vertebrates - animals with backbones)
- Class Conodonta (Conodonts)
- Class Cephalaspidomorphi (jawless fish)
- Class Pteraspidomorphi (Paleozoic jawless fish)
- Infraphylum Gnathostomata (jawed vertebrates)
- Class Placodermi (Paleozoic armored forms)
- Class Chondrichthyes (cartilaginous fish)
- Class Acanthodii (Paleozoic "spiny sharks")
- Superclass Osteichthyes (bony fishes)
- Class Actinopterygii (ray-finned fish)
- Class Sarcopterygii (lobe-finned fish)
- Superclass Tetrapoda (four-legged vertebrates)
Phylogeny
Chordata
├─Urochordata (tunicates)
├─Cephalochordata (lancelets)
└Craniata (animals with skulls)
├─Myxini or Hyperotreti (hagfish)
└Vertebrata (animals with backbones)
├─Conodonta (Conodonts)
├─Cephalaspidomorphi (Paleozoic jawless fish)
├─Hyperoartia (lampreys and kin)
├─Pteraspidomorphi (other Paleozoic jawless fish)
└Gnathostomata (jawed vertebrates)
├─Placodermi (Paleozoic armored forms)
├─Chondrichthyes (cartilaginous fish)
└Teleostomi (advanced fishes and their descendants)
├─Acanthodii (Paleozoic "spiny sharks")
└─Osteichthyes (bony fishes)
├─Actinopterygii (ray-finned fish)
└─Sarcopterygii (lobe-finned fish)
└Tetrapoda (four-legged vertebrates)
├─Lissamphibia (frogs and kin)
└Amniota (amniotic egg)
├Synapsida (mammals and kin)
└Sauropsida (reptiles and birds)
Note: Lines show probable evolutionary relationships (including extinct members of taxa)
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