Drop a trawl net into Japanese waters, and you just might pull up the doomed soul of a Samurai warrior – as local lore has it, that is. For hidden in the murky depths is a species of ghost crab that’s long been linked to a ghost story all its own: Heikeposis japonica, the “samurai crab.”
The story begins with the battle of Dan-no-ura in 1185 AD, a war in which two powerful Samurai clans: the ruling Taira clan (also known as Heike), and the challengers, Minamoto, fought over the Japanese imperial throne. Though the Heiki clan, led by child-Emperor Antoku and his grandmother, had ruled for decades, they found themselves massively outnumbered during the battle.
Rather than allowing their emperor to be captured, a member of the royal household allegedly took Antoku from his bed and drowned him in the bordering sea. Plagued by grief, Antoku’s grandmother followed him to Davy Jones’ locker, calling upon any Samurai who hadn’t yet been slain in battle to join her in death. While Antoku eventually came to be worshiped as the god of water (Mizu-no-kami), the Samurai would live on, doomed to walk the earth for all of eternity in the form of the ghost crabs who feasted on their bodies. Legend has it, they scuttle the oceans to this day searching for remnants of their once-great empire. (Cue Vincent Price laugh.)
The Tale of Heike. Image: Utagawa Kuniyoshi
It’s a great tale, but interestingly, this fish story may have brought itself to life in the form of a human-triggered evolutionary shift known as artificial, or “inadvertent character” selection. We bipedal primates are great at finding faces in the faceless. The psychological phenomenon, known as pareidolia, is the same reason we see crabs in Mars photos (read: no, we did not find crabs on mars), or smileys in space (that one we did find).
Over the centuries, Japanese fishermen have released any Heikeposis crabs whose carapaces (in their eyes) resembled Samurai battle masks. Some postulate that in doing so, the fishermen actually influenced the direction of natural selection. By removing only the crabs that didn’t look like doomed warriors come-a-calling from the local ecosystem, humans could have increased the likelihood that future generations of ghost crab would inherit the Samurai trait.
Artificial selection is very real, and in fact, most of us have great examples of it in our homes: pets. Over the years, we’ve guided the evolution of domestic animals to our liking via artificial selection, but the theory that the Heikeposis crab “battle masks” arose the same way has a few holes. Some, including invertebrate researcher Michael Bok have questioned whether or not Heikeposis crabs would have been eaten at all, given their incredibly small size.
“These crabs only reach a maximum carapace length of 1.2 inches,” he writes. “Anyone who has eaten steamed crabs can immediately recognize that such a minuscule crab as H. japonica is not worth the effort it would take to extract its meat.”
Given the things humans have taken to eating over the years, from tiny insects to the uni on your sushi dinner, I’m not sure that hypothesis completely rules out artificial selection. But Bok does raise a stronger point: many marine species, and even some other crabs, rock the Samurai look – even those inhabiting waters far offshore, away from commercial fisheries or coastal communities. The grooves you see are indications of muscle attachment sites, or apodemes, under the carapace.
The most likely explanation? These crabs always looked like badass mofos, it just took a bit of folklore battle for us to notice them.
Featured Image: Corinne Okada/Flickr