Chordate

Chordates

Yellowfin tuna, Thunnus albacares

Scientific classification

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

Typical Classes

Subphylum Urochordata - Tunicatas
- Ascidiacea
- Thaliacea
- Larvacea
Subphylum Cephalochordata - Lancelets
Subphylum Vertebrata - Vertebrates
- Myxini
- Conodonta
- Hyperoartia
- Cephalaspidomorphi
- Pteraspidomorphi
- Placodermi
- Chondrichthyes
- Acanthodii
- Actinopterygii
- Sarcopterygii
- Amphibia
- Sauropsida
- Synapsida
- Aves
- Mammalia

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, 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 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.

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)

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)

Class Amphibia (amphibians)

Series Amniota (amniotic egg)

Class Synapsida (mammal-like reptiles)

Class Mammalia (mammals)

Class Sauropsida - (reptiles)

Class Aves (birds)

External links

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