The document summarizes the characteristics of the phylum Chordata. There are seven main classes of chordates: 1) Agnatha - Jawless fish with a notochord but no jaws, scales or fins. They have gills and are marine or freshwater ectotherms. 2) Condrichythes - Sharks, rays and skates with cartilage skeletons, paired fins, placoid scales and teeth that point inward. They are marine ectothermic carnivores or filter feeders. 3) Osteichthyes - Bony fish with paired fins, scales, swim bladders, chromatophores and lateral lines. They can be marine or fresh