Vertebrate

Vertebrates (ˈvɜrtəbrɪts,_-ˌbreɪts) are animals with spinal cords and bony or cartilaginous backbones, including all mammals, birds, reptiles, amphibians and fish. The vertebrates consist of all the taxa within the subphylum Vertebrata (ˌvɜrtəˈbreɪtə) (chordates with backbones) and represent the overwhelming majority of the phylum Chordata, with currently about 69,963 species described. Vertebrates comprise such groups as the following: jawless fish, which include hagfish and lampreys jawed vertebrates, which include: cartilaginous fish (sharks, rays, and ratfish) bony vertebrates, which include: ray-fins (the majority of living bony fish) lobe-fins, which include: coelacanths and lungfish tetrapods (limbed vertebrates) Extant vertebrates range in length from the frog species Paedophryne amauensis, at as little as , to the blue whale, at up to . Vertebrates make up less than five percent of all described animal species; the rest are invertebrates, which lack vertebral columns. The vertebrates traditionally include the hagfish, which do not have proper vertebrae due to their loss in evolution, though their closest living relatives, the lampreys, do. Hagfish do, however, possess a cranium. For this reason, the vertebrate subphylum is sometimes referred to as "Craniata" when discussing morphology. Molecular analysis since 1992 has suggested that hagfish are most closely related to lampreys, and so also are vertebrates in a monophyletic sense. Others consider them a sister group of vertebrates in the common taxon of craniata. The word vertebrate derives from the Latin word vertebratus (Pliny), meaning joint of the spine. Vertebrate is derived from the word vertebra, which refers to any of the bones or segments of the spinal column. Vertebrate anatomy All vertebrates are built along the basic chordate body plan: a stiff rod running through the length of the animal (vertebral column and/or notochord), with a hollow tube of nervous tissue (the spinal cord) above it and the gastrointestinal tract below.