Chordates, members of the animal phylum Chordata, which includes all mammals, birds, amphibians, reptiles, and fish. There are about 45,000 species of chordates. They are classified in four subphyla, the largest of which contains the vertebrates. All chordates share three basic characteristics. The first characteristic is a single dorsal nerve cord, which in mammals takes the form of the brain and spinal cord. The second is a flexible rod of cells called a notochord, which in vertebrates takes the form of the backbone. The third is the presence of gill slits at some stage during the development of the animal. All chordates have bilateral symmetry.
Termites have a bad rep for destroying homes, but are they actually that bad? What do you really know about the lowly termite? Learn more about this adaptable insect and how termite colonies function as a giant cooperative community by taking this quiz.
Amphibian, one of a large class of cold-blooded vertebrates (animals with backbones). They are fascinating creatures. Learn more about amphibians at HowStuffWorks.