Chordate
| Chordates |
|---|
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 </table> 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 tail extending past the anus, and bands of muscles that go around the body. 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 In vertebrates, the notochord has been replaced by a bony vertebral column.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 (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
- Testudines (turtles)
- Diapsida
- Lepidosauria (lizards, snakes, tuatara)
- Archosauria
- Crocodilia (crocodiles)
- Dinosauria
- Aves (birds)
- Synapsida