This Spike-Covered Worm Shows Just How Strange Prehistoric Life Could Be

History's most bizarre worm now has an even weirder new cousin. Last week, new research about the 500-million-year-old worm Hallucigenia made global headlines, thanks to the animal's notoriously trippy appearance.

Now, it seems that paleontologists have upped the ante with the discovery of a new Hallucigenia relative called Collinsium ciliosum, described in detail in a study published today in the Proceedings of the National Academy of Sciences.

According to study co-author Javier Ortega-Hernández, C. ciliosum is like "Hallucigenia on steroids."

"Collinsium and Hallucigenia are closely related," Ortega-Hernández told me over the phone. "However, there are some key differences. For example, Hallucigenia has two pairs of spines per each pair of legs, but Collinsium has up to five sets of spines per pair of legs. So, it's a lot more spiney."

Indeed, this newly-identified creature looks a walking pincushion with its heavily clustered armature of dorsal daggers. Like Hallucigenia, it thrived in the Cambrian period some half a billion years ago, though Collinsium predated its more famous relative by about 10 to 15 million years.

Its unusually prickly defense system suggests that Collinsium was more exposed to predators than Hallucigenia, and Ortega-Hernández and his team have a good idea of why that was the case.

"Back in the Cambrian, life was similar in certain ways to what we see now," he said. "The creatures were very different, but you have similar ecologies. Some of them were grazers, some of them were carrion-feeders, but the players themselves are quite distinct."

"In the case of Collinsium, our new fossil species, it has quite a peculiar morphology," Ortega-Hernández continued. "It has these six elongated, feather-like pairs of legs which are followed by nine pairs of shorter claw-like legs. We have interpreted this to mean that it probably would not have spent too much time in the muddy ocean bottom, but rather, it likely clung to sponges or something a bit higher up in the water column."

In this interpretation, Collinsium would perch itself atop a sponge, and hunker down with its claw-like appendages. It would then use its feathery front limbs to create a makeshift feeding basket that would capture nutrients by filtering them out of the water.

"This is interesting," noted Ortega-Hernández, "because this is a rather unique mode of feeding for this type of soft-bodied animal. It makes us wonder, well, why would you need these massive spines on your back if you are just filter-feeding?"

"Our idea there is that if it had to put itself itself in a higher position, then it would have been a lot more conspicuous to predators," he said. "You're more exposed if you are sitting on top of something [like a sponge] instead of hiding beneath it."

In other words, Collinsium invested in heavy back armor in order to reap the benefits of more unprotected locations in the Cambrian oceans. This is just the latest example of startling diversity displayed by early lobopodians, which is the group that includes both Collinsium and Hallucigenia.

"In terms of [lobopodian] distribution, we know from their spines that they were very widespread during the Cambrian both temporally and geographically," Ortega-Hernández told me. "We know they were all over the place, but we only have their complete body fossils from a few select localities."

In comparison, the only extant relatives of the group—velvet worms—are much more homogeneous, both in how they look and in where they choose to live.

"They are kind of cute and funny," said Ortega-Hernández, describing these modern lobopodians. "They look a little like long caterpillars with several pairs of legs and they have this peculiar hunting strategy of shooting slime at their prey."

"But what is interesting is that [velvet worms] are very similar in their construction," he continued. "They only change slightly in the number of legs they have and the coloration they may display. By contrast, we have these Cambrian animals like Collinsium and Hallucigenia that were a lot more diversified in their ecology and their adaptations."

"This is something that would be impossible to tell just from looking at extant velvet worms themselves," he added. "We have to look at the fossil record to gain this insight."

As always, the more paleontologists probe the murky Cambrian world, with its outlandish creatures and fascinating ecosystems, the more they can contextualize the vast diversity of life that has since evolved from it.