∞ generated and posted on 2016.11.06 ∞

Non-tetrapod, craniate chordates.

If something is a vertebrate then it is either a fish or it is the descendant of a fish. By and large, the fish are animals that both live in the water and, as a lineage, never left the water.

Thus, among the vertebrates there are fish and there are tetrapods, with sometime in the distant past, i.e., at approximately the point of tetrapod origin, the dividing line between, say, a fish and an amphibian was not quite as clear as it is today.

See alternatively fluorescent in situ hybridization, i.e., "FISH".