India, June 5 -- There are aliens, of a kind, among us.

Some creatures on our wild, wonderful planet are so strange, they could just as well have come from outer space.

One kind of sea slug can separate its head from its body, and then shuffle away, to regrow itself in its entirety. (Read Have you lost your head? alongside)

Sharks evolved so long ago, they predate our current North Star. (There's more on that alongside too.)

Tardigrades are microscopic invertebrates that can survive boiling water, freezing temperatures, radiation and even a space vacuum, by entering a dormant state. They have no lungs or heart, and survive by absorbing oxygen through their bodies.

Crocodiles have not really changed their biology in over 240 million y...