Chordate
Urochordata - Tunicates
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 In vertebrates, the notochord has been replaced by a bony vertebral column.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
