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 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) are a group of animals that includes 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, 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 vertebrae. In vertebrates, the notochord has been replaced by a bony vertebrae.

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. 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.

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)
                • Reptilia (most modern reptiles)
                  • Anapsida
                    • Testudines (turtles)
                  • Diapsida
                    • Lepidosauria (lizards, snakes, tuatara)
                    • Archosauria
                      • Crocodilia (crocodiles, alligators, caimans, gharials)
                      • Dinosauria
                        • Aves (birds)