Sazae-oni (栄螺鬼 lit. Turban Snail Ogre) are creatures from Japanese mythology, resembling large crustaceans.
Origin
They are a type of obake, forming when turban snails reach 30 years of age.
Appearance
Sazae-oni resemble large turban snail shells with an ogre inhabiting it, but they can alter their form to that of a beautiful woman.
Stories
The most popular legend of the Sazae-oni is that a group of pirates rescued a drowning woman from the sea and taking her back to his men. They vied for her attention, but soon found that she was willing to have sex with all of them, cutting their testicles off afterwards. The men, obviously upset, threw her into the ocean, where she revealed her true form, and bartered with the captain for their testicles back. The Sazae-oni ended up leaving with a large amount of pirate gold. Testicles are sometimes called kin-tama or "golden balls" in Japanese, so the punchline goes that gold was bought with gold.