Difference between revisions of "Chordate" - New World Encyclopedia
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{{Taxobox_begin | color = pink | name = Chordates}} | {{Taxobox_begin | color = pink | name = Chordates}} | ||
{{Taxobox_image | image = [[Image:Tuna.jpg]] | caption = Yellowfin tuna, ''Thunnus albacares''}} | {{Taxobox_image | image = [[Image:Tuna.jpg]] | caption = Yellowfin tuna, ''Thunnus albacares''}} | ||
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{{Taxobox_end_placement}} | {{Taxobox_end_placement}} | ||
{{Taxobox_section_subdivision | color = pink | plural_taxon = Typical Classes}} | {{Taxobox_section_subdivision | color = pink | plural_taxon = Typical Classes}} | ||
| − | * Subphylum [[Tunicata|Urochordata]] - [[ | + | * Subphylum [[Tunicata|Urochordata]] - [[Tunicate]]s |
** [[Ascidiacea]]* | ** [[Ascidiacea]]* | ||
** [[Thaliacea]]* | ** [[Thaliacea]]* | ||
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** [[Mammal]]ia | ** [[Mammal]]ia | ||
{{Taxobox_end}} | {{Taxobox_end}} | ||
| − | '''Chordates''' (phylum '''Chordata''') are a group of | + | '''Chordates''' (phylum '''Chordata''') are a group of [[animal]]s that includes all the [[vertebrate]]s (subphylum Vertebrata), as well as two sub-phylum of [[invertebrate]]s, the [[Urochordata]] (tenicates) and the [[Cephalochordata]] (lancelets). |
| − | + | The distinguishing features of chordates is that they all have, at some time in their life, a [[notochord]], a hollow dorsal nerve cord, pharyngeal slits, and a tail extending past the anus. A notochord is a flexible, rod-shaped body found in chordate embryos and composed of [[cell (biology)|cell]]s derived from the mesoderm. 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. | |
| + | ==Classification== | ||
The phylum Chordata 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. | The phylum Chordata 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. | ||
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The extant groups of chordates are related as shown in the [[phylogenetic tree]], below. They do not match up very well with the traditional groups, and as a result vertebrate classification is in a state of flux, although their relationships are not very well understood. | The extant groups of chordates are related as shown in the [[phylogenetic tree]], below. They do not match up very well with the traditional groups, and as a result vertebrate classification is in a state of flux, although their relationships are not very well understood. | ||
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'''Phylum Chordata''' | '''Phylum Chordata''' | ||
:'''Subphylum [[Urochordata]]''' - [[Tunicata|Tunicate]]s | :'''Subphylum [[Urochordata]]''' - [[Tunicata|Tunicate]]s | ||
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| − | {{ | + | {{credit3|Chordate|61718799|Notochord|90247694|Pharyngeal_slit|88021748}} |
[[Category:Life sciences]] | [[Category:Life sciences]] | ||
Revision as of 21:57, 26 November 2006
| Chordates | ||||||||
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 Yellowfin tuna, Thunnus albacares | ||||||||
| Scientific classification | ||||||||
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| Typical Classes | ||||||||
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Chordates (phylum Chordata) are a group of animals that includes all the vertebrates (subphylum Vertebrata), as well as two sub-phylum of invertebrates, the Urochordata (tenicates) and the Cephalochordata (lancelets).
The distinguishing features of chordates is that they all have, at some time in their life, a notochord, a hollow dorsal nerve cord, pharyngeal slits, and a tail extending past the anus. A notochord is a flexible, rod-shaped body found in chordate embryos and composed of cells derived from the mesoderm. 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.
Classification
The phylum Chordata 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.
The chordates and two sister phyla, the hemichordates and the echinoderms, make up the deuterostomes, a superphylum.
It has been theorized that the phylum originated as a result of paedomorphy occurring in a primitive ancestral form.
The extant groups of chordates are related as shown in the phylogenetic tree, below. They do not match up very well with the traditional groups, and as a result vertebrate classification is in a state of flux, although their relationships are not very well understood.
Phylum Chordata
- Subphylum Urochordata - Tunicates
- Subphylum Cephalochordata - Lancelets
- (unranked) Craniata (animals with skulls)
- Class Myxini or Hyperotreti (hagfish)
- Subphylum Vertebrata (Vertebrates - animals with backbones)
- Class Conodonta (Conodonts)
- Class Cephalaspidomorphi (Paleozoic jawless fish)
- Hyperoartia (lampreys and kin)
- Class Pteraspidomorphi (other Paleozoic jawless fish)
- Infraphylum Gnathostomata (jawed vertebrates)
- Class Placodermi (Paleozoic armoured forms)
- Class Chondrichthyes (cartilaginous fish)
- Class Acanthodii (Paleozoic "spiny sharks")
- (unranked) Teleostomi (advanced fishes and their descendents)
- Superclass Osteichthyes
- Class Actinopterygii (ray-finned fish)
- Class Sarcopterygii (lobe-finned fish)
- Superclass Tetrapoda (four-legged vertebrates)
- Superclass Osteichthyes
- (unranked) Teleostomi (advanced fishes and their descendents)
External links
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