Kechi (けち) is one of the most useful Japanese words you're ever likely to find. It means cheap or stingy, but isn't limited to just money. It expands to include emotion, time, and helpfulness among others.
Futakuchi-onna (two-mouthed woman) is all about the kechi. In one tale, faced with a food shortage, she stuffs her own child while letting her stepchild waste away. In another, she withholds food from herself, trying to please either her miserly husband or her own stinginess. Self-denial manifests as a separate ravenous mouth on the back of her head, grumbling and mumbling and, finally, satisfying itself.
It's difficult not to associate the Futakuchi-onna with modern eating disorders and standards of beauty. Hunger-abstained bursts out from the flesh gibbering and gnawing - a metaphor for either the cause or the disease. All grabbing tentacles and unthinking appetite, the jellyfish seemed the perfect choice for the zoological avatar.