Chordates
Fossil range: Latest
Ediacaran - Recent |
![Yellowfin tuna, Thunnus albacares](./modules/Fish-MM/images/200px-Tuna.jpg)
Yellowfin tuna, Thunnus albacares
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Scientific classification |
Domain: |
Eukaryota
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Kingdom: |
Animalia
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Subkingdom: |
Eumetazoa
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(unranked) |
Bilateria
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Superphylum: |
Deuterostomia
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Phylum: |
Chordata
Bateson, 1885 |
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Typical Classes |
See
below |
Chordates (phylum
Chordata) are a group of animals that includes the
vertebrates, together with several closely related
invertebrates. They are united by having, at some time in
their life, a notochord, a hollow dorsal nerve cord,
pharyngeal slits, an endostyle, and a muscular tail
extending past the anus. Some scientists argue that the true
qualifier should be pharyngeal pouches rather than slits.
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 vertebrae. 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.
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.
Classes of Chordata
In the subphylum
Urochordata classes Ascidiacea, Thaliacea, Larvacea are
found. Includes the sea squirts and tunicate worms.
In subphylum
Cephalochordata, the worm-like lancelets are found.
In the subphylum Vertebrata (all animals with vertebrae)
classes 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) are found.
Taxonomy & Phylogeny
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)
├─(unranked) Hyperoartia (lampreys and kin)
├─Class Pteraspidomorphi (other Paleozoic jawless fish)
└Infraphylum Gnathostomata (jawed vertebrates)
├─Class Placodermi (Paleozoic armoured forms)
├─Class Chondrichthyes (cartilaginous fish)
└(unranked) Teleostomi (advanced fishes and their descendants)
├─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 Mammalia (mammals)
└Class Sauropsida - (reptiles)
└Class Aves (birds)
Note:Lines show assumed evolutionary relationships
(including extinct members of taxa)
External links