Chordate Did You Mean Chordate?

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Chordates

Image:Tuna.jpg

Yellowfin tuna, Thunnus albacares

Scientific classification

Kingdom:	Animalia
Superphylum:	Deuterostomia
Phylum:	Chordata Bateson, 1885

Typical Classes

Subphylum Urochordata - Tunicatas
Subphylum Cephalochordata - Lancelets
Subphylum Myxini - Hagfishes
Subphylum Vertebrata - Vertebrates
- Petromyzontida - Lampreys
- Placodermi (extinct)
- Chondrichthyes - Cartilaginous fishes
- Acanthodii (extinct)
- Actinopterygii - Ray-finned fishes
- Actinistia - Coelacanths
- Dipnoi - Lungfishes
- Amphibia - Amphibians
- Reptilia - Reptiles
- Aves - Birds
- Mammalia - Mammals

Chordates (phylum Chordata) include the vertebrates, together with several closely related invertebrates. They are united by having, at some stage in their life, a notochord, a hollow dorsal nerve cord, pharyngeal slits, a dorsal hollow neural tube, and a muscular tail extending past the anus. Some scientists argue, however, 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 In vertebrates, the notochord has been replaced by a bony vertebral column.

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 very well understood.

Chordata

Urochordata (tunicates)
Cephalochordata (lancelets)
Craniata (animals with skulls)
- Myxini or Hyperotreti (hagfish)
- Vertebrata (animals with backbones)
  - Cephalaspidomorphi (lampreys)
  - Gnathostomata (jawed vertebrates)
    - Chondrichthyes (cartilaginous fish)
    - Teleostomi (bony fish, ~ Osteichthyes)
      - Actinopterygii (ray-finned fish)
      - Sarcopterygii (lobe-finned fish)
        
        Actinistia (coelacanths)
        
        Dipnoi (lungfishes)
    - Tetrapoda (four-legged vertebrates)
      - Amphibia (amphibians)
      - Amniotes (amniotic egg)
        
        Synapsida
        
        Mammalia (mammals)
        
        Anapsida
        
        Testudines (turtles)
        
        Diapsida
        
        Reptilia (most modern reptiles)
        
        Lepidosauria (lizards, snakes, tuatara)
        
        Archosauria
        
        Crocodilia (crocodiles, alligators, caimans, gharials)
        
        Dinosauria
        
        Aves (birds)

Wikispecies

Wikispecies has information on:

Chordata

Wikibooks

Wikibooks has a Dichotomous Key related to this taxon:

Chordata

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