Even the top predators of the ancient seas, such as these phallus-shaped worms, needed to be protected. The Cambrian epoch (543 million to 490 million years ago) saw the first big boom of biodiversity on Earth, with the progenitors of almost all extant species arriving for the first moment. The penis parasite was one of the most dreaded among them.
Penis worms, also known as priapulids and named after Priapus, the well-endowed Greek god of male genitals, are a group of marine worms that have endured on the world’s shores for 500 million years. Their prevailing descendants reside in muddy burrows deep underwater, where their floppy, phallus-shaped bodies occasionally frighten fishers. Penis worms, however, were once a scourge of the ancient seas, widely dispersed over the world and equipped with extendible, fang-lined mouths that could consume any poor marine creature that crossed them, according to relics dating back to the early Cambrian.
Penis worms, as dangerous as they were, were not without terror. Investigators uncovered four priapulid fossils nestled between the cone-shaped shells of phytoliths, a long-extinct genus of marine animals, in a new investigation published Nov. 7 in Current Biology. Because all worms were discovered in the same sort of shell and about a similar place, the scientists believe the worms had adopted the shells as their homes, similar to how current hermit crabs do. If that’s the case, penile worms may have originated the “hermit” lifestyle hundreds of millions of years before the crustaceans who popularised it.
In an email statement, research co-author Martin Smith, an associate professor of paleontology at Durham University in England, stated, “The only explanation that made sense was that these shells were their homes – something that came as a genuine surprise.” The four hermit penis fossils were discovered in the Guanshan fossil beds in southern China by the researchers. These early Cambrian (approximately 525 million years ago) fossil strata are known for retaining complex features like teeth and shells and soft tissue like priapulid bodies, which are considerably harder to locate in the fossil record.
The worm’s bottom is squeezed into the cone’s bottom while the worm’s head and mouth dangle out over the side, like a melting swirl of soft-serve ice cream in each shell. According to the researchers, the ancient site had dozens of additional empty shells but no free-living priapulids, implying that the two were not connected by chance.
Furthermore, each worm was snugly encased in its sheath, implying that the organisms picked their shells for long-term protection against Cambrian predators rather than as a temporary haven. The finders believe that this form of “hermiting” behavior was never documented in priapulids or other species until the Mesozoic era (250 million to 65 million years ago). Smith finds it “mind-boggling” that such complex behavior could have arisen so quickly after the Cambrian explosion, which occurred more than 500 million years ago. Even dangerous penis worms had to get imaginative in the harsh habitat of the early seas.