Sazae-oni

shellfish ogre) are creatures from Japanese mythology, resembling large mollusks.

[1] They are a type of obake that forms when turban snails, especially Turbo sazae, reach 30 years of age.

The most popular legend of the Sazae-oni is that of a group of pirates who rescued a drowning woman from the sea and took her back to the ship.

The men, obviously upset, threw her into the ocean, where she revealed her true form, and bartered with the captain for their testicles back.

[2][3] Other legends of these creatures depict them wandering into coastal or seaside inns whilst in human guise, whereupon they devour the innkeeper in the night and then escape before morning.