Horror, Sleaze and Trash.

Heikegani: The Samurai Ghost Crabs

Heikegani is a species of crab native to Japan, with a shell that bears a pattern resembling a human face. According to Japanese folklore, the Heikegani crabs contain the souls of the Heike samurai warriors who were slain at the Battle of Dan-no-ura in 1185 AD, a war over the Japanese imperial throne.

According to the theory of Artificial Selection, the fishermen fishing Japan’s waters would throw back any crabs whose shells looked like a samurai’s face out of respect for the fallen heike. This preserved the DNA of the heikegani with samurai-like faces while thinning the genetic lines of those without. 

The problem with this theory is that the Heikegani crabs, which have a maximum length of 1.2 inches, are too small to be eaten, so it is unlikely they were ever caught for food in the first place.
A far more plausible theory is that any resemblance of a human face seen in the shells of the Heikegani crabs is the result of pareidolia, the human brain’s innate ability to recognize faces and human forms in a set of random stimuli. Common examples include seeing images of animals or faces in clouds, the Virgin Mary on toast, and the man in the moon. (Source)