Argonaut

An argonaut is also known as a paper nautilus. It's a cephalopod, but it's not a nautilus. Nor is it a squid or cuttlefish, but it has a shell. Argonauts are octopuses with shells. The shells they make are not related at all to other cephalopod shells. The argonauts paper-like shells were developed independently after shell-less cephalopods evolved. Argonauts are strange even among octopuses, but wait until you hear about their bizarre sex lives. The video is less than ten minutes long, the last part is an ad. (via Laughing Squid)