Phylum Chordata is a group of animals characterized by having a notochord, a dorsal nerve cord, pharyngeal slits, and a post-anal tail at some stage of their development. This phylum includes a diverse range of species, from fish and amphibians to birds and mammals. Chordates are divided into three main subphyla: Cephalochordata (lancelets), Urochordata (tunicates), and Vertebrata (vertebrates). The vertebrates, which include humans, are the most complex and have a backbone that protects the spinal cord. Chordates play essential roles in ecosystems and have significant importance in biological research and conservation.