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Vertebrate
Vertebrates comprise any species of animals within the subphylum Vertebrata (chordates with backbones). Vertebrates represent the overwhelming majority of the phylum Chordata, with currently about 64,000 species described. Vertebrates include the jawless fish and the jawed vertebrates, which includes the cartilaginous fish (sharks and rays) and the bony fish. A bony fish clade known as the lobe-finned fishes is included with tetrapods, which are further divided into amphibians, reptiles, mammals, and birds. Extant vertebrates range in size from the frog species ''Paedophryne amauensis'', at as little as , to the blue whale, at up to . Vertebrates make up about 4% 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, 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 the 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.
== Etymology ==
The word ''vertebrate'' derives from the Latin word ''vertebratus'' (Pliny), meaning ''joint of the spine.'' It is closely related to the word ''vertebra'', which refers to any of the bones or segments of the spinal column.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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