Tetraodontidae
These mysterious circles on the seafloor are not caused by aliens—it's actually pufferfish hoping to snag a new mate. Divers first noticed the structures near Japan's Amami-Oshima Island about 20 years ago. Nobody knew what was creating them until recently when scientists discovered that male pufferfish spend about 10 days carefully constructing and decorating the structures to woo females.
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