“The Heike crab” or “the samurai crab” is famous because it looks like samurai warriors from the beginnings of last millenium. As Carl Sagan explains in his book, Heike clan warriors lost everything in a decisive battle against the Genji. That battle was on 1185 near Japanese coaste. Most of the corpses stayed for long around the beaches where the battle occurred.
Local fishermen living started believing that the spirits from those dead Heike warriors were living inside crabs that had some similarities with a human face. An artificial selection process was triggered because fishermen were returning those human-like crabs to the sea and eating “normal” crabs. Doing that for centuries “created” not only human-face crabs but even Heike-samurai-face crabs! And of course, those are the ones who survive.
Heike warrior’s face.
Non-scientific explanation, the fishermen’s legend says that those crabs are real Heike warriors transformed. There are eve traditional Japanese fold tales where crab armies return to fight against the Genji. Next ukiyo-e paint represents some Heike phantom ships and Heike crabs attacking the Genji army.
If you wanna listen Carl Sagan’s explanation that is better than mine, watch next video: