Marine vertebrate
Marine vertebrates are vertebrates that live in marine environments, which include saltwater fish (including pelagic, coral and deep sea fish) and marine tetrapods (primarily marine mammals and marine reptiles, as well as semiaquatic clades such as seabirds). As a subphylum of chordates, all vertebrates have evolved a vertebral column (backbone) based around the embryonic notochord (which becomes the intervertebral discs), forming the core structural support of an internal skeleton, and also serves to enclose and protect the spinal cord.