We were swimming in the sea not so far from our house, when Aya shouted that she’d found a weird shell floating in the water. At first we thought it was a plastic toy but it seemed to be natural, although it was unlike any shell I’d ever seen. After going home, we looked in our sealife book and found out that it was the egg-case of a Greater Argonaut, which is a kind of octopus. The female produces this papery egg-case, which makes it look like a nautilus. There’s an interesting Wikipedia article about it: here.
I think this is probably one of the most beautiful objects, natural or artificial, I’ve ever seen.
Mollusca: Cephalopoda: Octopoda: Argonautidae
Greater Argonaut = aoigai
Location: Beach near Kanezaki (Google map)