Chordata is a phylum of animals, named after their possession of a notochord at some point during their lives (embryonic, juvenile, or adult). Chordates have four other unifying characteristics, also possessed at some life stage: a dorsal nerve cord, an endostyle, a post-anal tail, and pharyngeal pouches. Many chordates have a spinal column, and are therefore vertebrates.
The phylum includes several classes, the most well-known of which are vertebrates:
- Mammalia - the mammals, such as the cats and the great apes
- Aves - the birds
- Reptilia - The reptiles, such as the (extinct) dinosaurs
- Amphibia - the amphibians (such as frogs, newts and salamanders)
- Pisces - the fish
Scientists believe that the chordata are closest to the arthropoda (shelled, joint-legged animals such as insects and crustaceans), echinodermata (spiny-skinned animals such as starfish and sea urchins), and annelida (earthworms) in biology, due to common features such as segmentation, which are not seen in other phyla such as the mollusca (molluscs) or coelenterata (jellyfish and sea anemones).