Chordate

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• 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) 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.

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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 In vertebrates, the notochord has been replaced by a bony vertebral column.

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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 very well understood.

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Chordata

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• 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)

Phylum: Phylum may refer to the following:...

Invertebrate: Invertebrate is a term coined by Jean-Baptiste Lamarck to describe any animal without a spinal column. It therefore includes all animals except vertebrates (fish, reptiles, amphibians, birds and mammals)....

Notochord: The notochord is a flexible rod-shaped body found in embryos of all chordates. It is composed of cells derived from the mesoblast and defining the primitive axis of the embryo. In lower vertebrates, it persists throughout life as the main axial support of the body, while in higher vertebrates it is ...