Heikegani

In 1185, at Dan-no-ura in the straits off Shimonoseki, the Taira clan was destroyed at sea.

It's the end of the Genpei War and the most famous battle in Japanese history. The Taira fleet was broken, the tide turned against them, and the clan went into the water. The child emperor Antoku — six years old — was drowned by his own grandmother, who took him in her arms and stepped over the side rather than let him be captured.

And the crabs in those straits have faces on their shells.

Not vaguely. A scowling, furrowed, wide-jawed human face, in relief, angry — unmistakably a warrior's expression, and enough like a Noh mask that the resemblance is almost rude.

The verdict has stood for eight hundred years: the Taira are still down there, wearing their war faces.

It's a real animal

This is what makes the heikegani unlike almost everything else in this collection. It isn't a story about something. You can catch one.

Heikeopsis japonica is a real crab, in real waters, sold in no market and photographed constantly. The folklore is attached to a specimen you can hold.

Lafcadio Hearn used exactly this seascape to open his most famous ghost story — the tale of the blind lute-priest Hōichi, who was summoned night after night to perform the epic of the Taira for an audience he could not see, and who turned out to be playing in a graveyard to the dead of that battle. Hearn notes the crabs of that shore, said to carry the spirits of the Heike warriors on their backs.

The legend about the legend

And now the part I think is the best thing on this page.

Carl Sagan told this story in Cosmos, and told it beautifully. His version: for centuries, fishermen in those straits who pulled up a crab with a samurai face on it would throw it back, out of respect for the dead. Crabs with less face-like shells got eaten. Generation after generation, the fishermen were unwittingly applying selection pressure — and over eight hundred years they bred the samurai face into existence.

Artificial selection, performed accidentally, by reverence. It's a wonderful illustration and it made the heikegani famous worldwide.

The rebuttal, from the carcinologist Joel Martin, is unfortunately airtight.

Heikegani are far too small to eat. Nobody was ever culling them, because nobody was ever keeping them — so there is no selection pressure to speak of. And the ridges that make the "face" are muscle-attachment structures, present in related crab species all over the world, including in waters where nobody has ever heard of the Taira.

The face is pareidolia. Human beings are exceptionally good at seeing faces in things, and the crab's anatomy happened to line up.

So we end with something rather perfect. A folk belief about warrior ghosts, attached to a real animal, explained by a modern scientific story that was itself not true — and that story is now more widely believed than the folklore it was explaining.

A legend about a legend. The heikegani has accreted a second layer of myth inside living memory, and this one came from a television programme about science.