is a species of crab native to Japan, with a shell that bears a pattern resembling a human face (a case of pareidolia) which is interpreted to be the face of an angry samurai hence the nickname samurai crab. The crabs are named after the once powerful Taira clan which dominated medieval Japan, commonly known as the Heike. It is believed that these crabs are reincarnations of the Heike warriors defeated at the naval Battle of Dan-no-ura as told in The Tale of the Heike. While the crabs are edible, they are not eaten by most Japanese. Origin of the carapace pattern Heikegani were used by Carl Sagan in his popular science television series Cosmos: A Personal Voyage as an example of unintentional artificial selection, an interpretation originally published by Julian Huxley in 1952. According to this hypothesis, the crabs with shells resembling samurai were thrown back to the sea by fishermen out of respect for the Heike warriors, while those not resembling samurai were eaten, giving the former a greater chance of reproducing. Therefore, the more closely the crabs resembled a samurai face, the more likely they would be spared and thrown back. This idea has met with some skepticism. Joel Martin for instance notes that humans do not eat Heikegani, and as such there is no artificial pressure favoring face-like shell patterns, contrary to Sagan's implication. The pattern of ridges on the carapace serves a very functional purpose as sites of muscle attachment. Similar patterns are found on the carapaces of other species and genera throughout the world, including numerous fossil taxa. Battle of Dan-no-ura The Battle of Dan-no-ura was preceded by an immense struggle between the imperial rulers of Japan, the Taira clan (also known as the Heike), who the Heikegani crabs are named after, and the Minamoto clan (Genji), who were fighting for control of the throne at the end of the 12th century in the Genpei War (1180–1185). On the 24th of April, 1185 AD, two powerful Samurai clans fought to the death on the Dan-no-ura bay of Japan's Inland Sea. The ruling Taira clan (Heike) was led by their child-Emperor, Antoku, and his grandmother, Taira no Tokiko. The Heike had ruled Japan for many decades, but now, massively outnumbered, they faced defeat at the hands of the Minamoto. During the battle, Tokiko took the seven-year-old Emperor Antoku and leaped with him into the water