JELLYFISH

Jellyfish are among the oldest animals that still inhabit the planet today. They were present before what paleontologists call the Cambrian explosion when, suddenly, representatives of the ancestors of all current animals are found in the fossil remains. Before that, in the fossil record, either animals were found that left no descendants, or jellyfish were found. Almost the same as the current ones. Which means that half a billion years of natural selection hasn't pushed them to change.