Phylum Chordata includes animals that possess a notochord, a flexible rod-like structure that provides support during development. Members of this phylum also have a dorsal nerve cord, pharyngeal slits, and a post-anal tail at some stage of their life cycle. This group encompasses a wide variety of organisms, including mammals, birds, reptiles, amphibians, and fish. Chordates are divided into three main subphyla: Cephalochordata, Urochordata, and Vertebrata. The vertebrates, which include humans, are characterized by a backbone that replaces the notochord in adults. Chordates are found in diverse habitats, from oceans to forests, and play essential roles in ecosystems.