Neither character exists in any other living vertebrate. Other unique anatomical features include a hollow fluid-filled "notochord" (a primitive feature in vertebrates) underlying the spinal cord and extending the length of the body, vertebrae that are incompletely formed or totally lacking bony centra, an oil-filled gas bladder, fleshy "lobed" or limb-like fins that are internally supported by bone, and paired fins that move in a synchronized tetrapod-like pattern