Vertebrates Animals with Backbones, and Their Relatives
• PHYLUM 9. CHORDATA OR CHORDATES.
This is our own phylum. Besides us and the other mammals, it includes the fishes, amphibians, reptiles and birds and some extinct forms. Besides these, the Chordata include some creatures that nobody but a zoologist notices. These are the sea-loving subphylum Protochordata.
Chordates have three germ layers. They have two side symmetry and at least some degree of segmentation. There is a coelom, and the various systems of organs are highly developed. There is always an internal skeleton, although in the humblest species this is only a rod or cord of cartilage along the back. In higher chordates the rod is a jointed backbone enclosing a nerve cord with a brain at the fore end.
There are about 60,000 species of chordates.
BY ARCHIE CARR