Axolotl. Ambystoma mexicanum. What is it? It belongs to the salamanders, but. A salamander is a creature that has some properties and life history. Your garden-variety salamander starts life as an egg, larvae, tadpole, metamorphosis, adult salamander. After metamorphosis the creature is an adult, crawls up on land and reproduce. That is the idea.
But there is this magnificent mechanism in evolution.. if (over time) the environment for the adults on land is too harsh, the juveniles can develop the ability to reproduce. They skip metamorphosis almost entirely, and stay in a juvenile “prepubescent” stage that should not allow them to reproduce, and yet they do. This is called neoteny.
Now this is all pretty simple, we could just say that the Axolotl is a creature that evolved to skip the land-living stage, and what is odd about that? That is kinda the essence of evolution. Obviously it is adult as long as it is able to reproduce. So it is just a pretty odd salamander. Or pretty odd cousin of the salamanders.
But, what dictates whether the Axolotl undergoes metamorphosis or not, is the level of iodine. So if you inject an Axolotl with iodine, it undergoes metamorphosis. And looks like a proper salamander, and do salamandery things.
I find that fascinating. I am sure biologists are laughing at me, but I find it wondrous. And they look magnificent.