Most people know jellyfish and their ilk — the cnidarians, of sea pen, anemone, coral, and man’o'war fame — live in water and (happily for us) stay pretty well confined to it. But as it turns out, that’s not entirely the case.
One of the most fascinating things about the history of life is the way distantly related species can look alike. In some cases, the similarities are superficial, and in other cases they are signs of a common ancestry. Sometimes it’s a little of both.