SoylentNews

DannyB [soylentnews.org] writes:

From Live Science.com: [livescience.com]

Ferocious 'penis worms' were the hermit crabs of the ancient seas [livescience.com]

[....] Technically known as priapulids — named for Priapus, the well-endowed Greek god of male genitals — penis worms, as they’re commonly known, are a division of marine worms that have survived in the world's oceans for 500 million years. Their modern descendants live largely unseen in muddy burrows deep underwater, occasionally freaking out fishermen with their floppy, phallus-shaped bodies. But fossils dating back to the early Cambrian [livescience.com] show that penis worms were once a scourge of the ancient seas, widely distributed around the world and in possession of extendible, fang-lined mouths that could make a snack out of the poor marine creature that crossed them.

But, fearsome as they were, penis worms themselves were not without fear. In a new study published Nov. 7 in the journal Current Biology, [doi.org] researchers discovered four priapulid fossils that were nestled into the cone-shaped shells of hyoliths, a long-extinct group of marine animals.

[....] In each shell, the worm's bottom sits squished into the bottom of the cone, while the worm's head and mouth dangle out over the side — sort of like a melting swirl of soft-serve ice cream. According to the researchers, the fossil region contained dozens of other empty shells, but no other free-living priapulids, suggesting the connection between the two was no mere accident. Furthermore, each worm fit snugly in its sheath, suggesting the creatures chose their shells for permanent protection from Cambrian predators, rather than as temporary refuge.

Penis worms were the hermit crabs of their time [cnn.com]

[....] "The only explanation that made sense was that these shells were their homes -- something that came as a real surprise," Smith said.

Hermiting behavior had been thought to evolve much later -- in the Jurassic Period about 170 million years ago -- deep into the time of the dinosaurs.

Behavior is one of the hardest things to infer from the fossil record. So how did researchers know for sure that the worms weren't using the shells as a temporary shelter, or while laying eggs, or as refuge from an environmental condition that caused their death?

"This was the big question we had to convince ourselves of in this study," Smith said via email.

[....] "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 (marine) animals arrive on the scene," he said.

The researchers also concluded that predators in this era must have been plentiful and aggressive, forcing the worms, which were 1 to 2 centimeters long and the width of a string, to take shelter in the empty shells.

[....] Today, penis worms are only found in settings where it's hard for predators to get a foothold, Smith said. Some are tiny and live between individual grains of sand. Others live in stinking, oxygen depleted and partially toxic waters. And they no longer take refuge in shells.

See also:

Phys Org: Study finds that ancient penis worms invented the 'hermit crab' lifestyle [phys.org]

Cosmos Magazine: Where’s Cambrian Willy? Inside a borrowed shell, it seems. [cosmosmagazine.com]

National Geographic: Cambrian Penis Worms Were Voracious Opportunists [nationalgeographic.com]

Related:

Image gallery: Bizarre Cambrian creatures [livescience.com]

Original Submission