And with the help of ingenious technology, researchers bring the armored worms virtually to life.

meet Lepidocoleus caliburnus and Lepidocoleus shurikenus: Two newly discovered species of worms that lived in shallow water near present-day Australia some 400 million years ago. Despite being classified as part of the worm family, they are nothing like today’s specimens. Because where these little creepers differ in particular is their bizarre armor.

Armored Worms

The researchers describe their finds in the scientific journal Papers in Paleontology. And the discovery of armored worms is quite special. “Worms are an incredibly diverse group,” Sarah Jacquet told Scientias.nl. “But these are really unique. That’s because they possess hard, outer armor. And armored worms are rather unusual. Lepidocoleus caliburnus and Lepidocoleus shurikenus are therefore the only worms known to have an external, hard, mineralized skeleton to protect the soft body beneath. This tells us something about their evolution and the need to have a protective suit of armor that would help them fend off attacks from an increasing number of predators.”

Naming
Lepidocoleus caliburnus is named after the famous sword ‘Excalibur’; in the Arthurian tales, the magical sword of King Uther Pendragon, who according to myth is the father of King Arthur. Lepidocoleus shurikenus owes its name to its appearance, as it resembles the Japanese ‘shuriken’ throwing knives.

The bizarre worms have unfortunately been extinct for millions of years now. “That is extremely unfortunate,” says Jacquet. Because that means that we can no longer study their beautiful armor in the flesh. Still, the researchers have found a way to bring the worms to life: virtually.

Virtually brought to life

Using X-ray microtomography, the researchers were able to produce digital 3D models of all individual armor plates. And that provides more insight into the armor of the worms. “Thanks to new technologies such as micro-CT, we can virtually separate the individual components of the armor,” explains Jacquet. “That allows us to see how it protected these worms until they sadly went extinct during one of the most significant mass extinctions of the past. The virtual models gave us insight into how the individual armor plates moved in relation to each other. We were also able to determine the degree of overlap between the plates.”

Lepidocoleus caliburnus. Image: University of Missouri

the armor

Thanks to this method, the researchers were able to reveal important features of the armor. Plus, they now have a better understanding of how the armor protected the worms. For example, the researchers found that the worms had two overlapping “armor systems”; one that ran along the entire skeleton of the worm and the other that covered both sides. “With this armor, the worms were able to prevent attacks from predators such as arthropods and bony fishes,” says Jacquet. “One of our studied specimens had curled up, which may indicate that the worms took this position when threatened. This is similar to how centipedes and woodlice still do today.”

Lepidocoleus shurikenus. Image: University of Missouri

While no direct correlations have yet been made between these worms and modern species, Jacquet believes her study could deepen our understanding of convergent evolution. “Convergent evolution is the evolution of similar traits across different, unrelated groups,” she explains. “While the armor is quite a unique adaptation — and one that was clearly useful in certain environments and provided protection from some predators — we’re seeing similar adaptations in a number of unrelated animal groups. Just think of various pangolins, woodlice and centipedes.”

Extinct

According to Jacquet, the fact that the worms were unable to escape mass extinction despite their strong armor is unfortunate, but understandable. “Ocean organisms were the hardest hit by such mass extinctions,” she says. “That’s because they often go hand in hand with phases of low oxygen concentrations in the ocean.”

However, research into the virtually brought to life worms continues. “We hope to understand even better how the armor protected against different types of attacks,” said Jacquet. “Think of situations where the worms were crushed, bitten or punctured. That will be the next, interesting step.”