What is "heikegani"

Heikegani (平家蟹, ヘイケガニ) (Heikeopsis japonica) is a species of crab native to Japan, with a shell that bears a pattern resembling a human face which many believed to be the face of an angry samurai hence the nickname Samurai Crab. It is locally believed that these crabs are reincarnations of the spirits of the Heike warriors defeated at the Battle of Dan-no-ura as told in The Tale of the Heike.