Animals in the Phylum Chordata may not all have a spine (which would classify them as a vertebrate animal), but they all have a notochord. The notochord is like a primitive backbone, and is present at least at some stage of their development.
So, while animals like humans, mammals and birds are all vertebrates in the Phylum Chordata, not all animals in the Phylum Chordata are vertebrates.
The Phylum Chordata contains 3 Subphyla: the familiar Subphylum Vertebrata (mammals, reptiles, birds, amphibians, and most fish), Subphylum Urochordata (tunicates, salps, and larvaceans), and Subphylum Cephalochordata (lancelets).
- Kingdom: Animalia
- Phylum: Chordata
- Classes (the classes in bold below include marine species): Actinopterygii (ray-finned fishes), Amphibia (amphibians), Appendicularia (pelagic tunicates), Ascidiacea (sessile tunicates), Aves (birds), Cephalaspidomorphi (lampreys), Cephalochordata (lancets), Elasmobranchii (sharks and rays), Holocephali (chimaeras), Mammalia (mammals), Myxini (Hagfishes), Reptilia (reptiles), Sarcopterygii (lobe-finned fish) and Thaliacea (salps).