According to a new study, living like a hermit has been around for half a billion years. About 500 million years ago during the Cambrian Period, a creature called a penis worm (also called Priapulida) was the first one to have invented the “hermit” lifestyle.
Penis worms are invertebrate, cylindrical creatures that look oddly similar to the male body part that they are named after. They have a powerful everting throat with sharp teeth. They first appeared not long after the Cambrian Explosion took place over 500 million years ago.
Scientists had already determined that hermit crabs used snail shells as a type of shelter against predators; however, a new study conducted by researchers from Durham University and Yunnan University revealed that penis worms also used that tactic hundreds of millions of years earlier. In fact, the “hermiting” lifestyle has never been discovered in any organism that was alive before the “Mesozoic Marine Revolution” that occurred between 251 and 66 million years ago.
But that all changed when researchers analyzed samples from China’s Guanshan fossil deposits which is well known because of the exceptionally well preserved soft tissues found there. Specifically, they studied four specimens of a penis worm called Eximipriapulus that were located inside of conical shells belonging to an extinct fossil group named hyoliths.
The fact that they were discovered inside of conical shells revealed to the researchers that these creatures did in fact live like a “hermit” half a billion years ago as stated by Dr. Martin Smith who is a co-author of the study, “The worms are always sitting snugly within these same types of shells, in the same position and orientation.”
Furthermore, their analysis suggested that there were many more predators during that time period than previously thought that forced the penis worms to hide in empty shells. “The only explanation that made sense was that these shells were their homes—something that came as a real surprise. Not long before these organisms existed, there was nothing alive more complex than seaweeds or jellyfish: so it's mind-boggling that we start to see the complex and dangerous ecologies usually associated with much younger geological periods so soon after the first complex animals arrive on the scene,” Dr. Smith explained.
This is a very significant discovery as there has never been any evidence of penis worms hiding in empty shells and living like hermits. The study was published in Current Biology where it can be read in full.
Pictures of the penis worm hiding in a hyolith shell can be seen here.