Discover the Crazy ‘Walking Worm’ With a Spiked Back 500 Million Years Old

© Dotted Yeti/

Written by Austin S.

Published: July 16, 2022

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Ever thought about how crazy it would be if worms had spikes? Meet the Hallucigenia, a weird walking worm with a spiked back.

The Hallucigenia is a genus of animals that was recognized as part of Paleozoic panarthropods. It existed about 500- 504 million years ago.

It has only three named species, H. sparsa, H. fortis, and H. hongmeia. They are all aquatic animals found at the bottom of the ocean. Their fossil was discovered in Canada and China. It took over 50 years to fully understand the structure of the Hallucigenia fully.

In this article, we’ll take you on a dive to the ocean floor to understand how this strange-looking creature survived and what its spikes were used for.

Description and Size

This organism was named Hallucigenia by the British Paleontologist Simon Conway. This was because of its bizarre and dream-like features.

The Hallucigenia is a genus of Cambrian animal that resembles worms. The Hallucigenea was a long tubular creature with up to ten pairs of thin legs. It belonged to a group of animals named lobopoda.

The first two or three legs of the organism are slender and featureless. They were closer to the feature recognized as its head. The remaining 7-8 pairs are found on the creature’s body, each terminated with 1 or 2 claws.

On the Hallucigenia’s trunk, there are 7 pairs of stiff conical spines. These spines corresponded to the 3rd- 9th leg pairs. The presence of the spines brought initial confusion about the erect position of the organism. The trunk appears featureless, but it is also argued that it was segregated by heteronomous annulations (ring formation).

Initially, it was challenging to identify the head and tail of the Hallucigenea. One of its ends droops down and extends far beyond its legs. However, further discoveries in the mid-2010s established that the longer end was the head. The actual head had an anteroventral mouth and a pair of simple eyes.

The Hallucigenia’s head shape varied between different species of the organism. It was elongated in Hallucigenia sparsa, rounded in Hallucigenia fortis, and unknown in Hallucigenia hongmeia. Radial and pharyngeal teeth were found within the front of the gut in Hallucigenia sparsa

The Hallucigenia was a relatively small creature. It had a length of 0.5-5.5cm (about 10-50mm)

  • Summary
    • Length – 0.5-5.5 cm
    • Skin – Soft and Spiky

The Hallucigenia was a relatively small creature. It had a length of 0.5-5.5cm (about 10-50mm)


Diet- What Did Hallucigenia Eat

The Hallucigenia was a detrivore. This meant that the organism obtained its nutrients by consuming decomposing plants and animals as well as feces. They occupied the bottom of the food chain.

Research showed that there are teeth in the mouth. However, the mouth parts also indicated that the animal ate by employing a suction mechanism. 

The ring of teeth present around the mouth showed that it most likely sucked in food and water. Also, the teeth around the throat region would have prevented food from moving backwards. This animal sucked all it could find and didn’t bother with chewing.

Habitat- When and Where Hallucigenea Lived

The Hallucigenia lived during the Cambrian period. This was around 508 million years ago.

The Cambrian period was described as the first geological period of the Paleozoic Era. It was also related to the Phanerozoic eon. The Cambrian period came with an explosion of biological diversity present to date. 

The Hallucigenia was an aquatic animal, and it was thought to have lived on the floor of the Cambrian oceans. However, its fossils were found in present-day Canada and China.

The Hallucigenia was a detrivore, and living on the ocean floor would have predisposed it to a lot of food. Scientists do not fully understand how the Hallucigenia found its way around in the dark, murky floor of the ocean. Which is justified because the animal had only a pair of simple eyes. 

However, the first two-three pairs of legs were thought to function as sensitive appendages. Hallucigenia must have used these appendages to relate to its environment.


The Hallucigenia was an aquatic animal that lived on the ocean floor.

©Dotted Yeti/

Threats and Predators

Hallucigenia is the lowest organism in its food chain. So, it is expected that this organism has a lot of predators. However, it had a few, as most of its predators would rather go for easier prey without spikes.

The Hallucigenia had two rows of spines on its body. These spikes were useful as a defense and in fending off predators such as the Anomalocaris. 

The Anomalocaris was at the top of the food chain in this ecosystem. It was the first apex predator. The Anomalocaris had compound eyes with thousands of lenses. This gave it an extremely sharp vision in the murky floor of the ocean.

The Hallucigenia had spines, but the Anomalocaris had spikes on its body and large hooked arms. So, the Hallucigenia wasn’t off the Anomalocaris’ menu.

However, researchers discovered that eyes were initially developed in the Cambrian period. This evolutionary development must have contributed to the success of the Hallucigenia and its predators in their environment.

It was less affected by natural threats to ocean life. This was because the Hallucigenia inhabited the ocean floor. 

For example, climate change; Climate change can increase temperatures on the surface of the ocean. However, no matter how warm the ocean surface gets, the temperature at the ocean beds is always slightly above freezing.

Discoveries and Fossils- When and Where It was Found

The first fossil was discovered in 1911 by an unnamed group of people. It was classified as an annelid worm. However, 66 years later, in 1977, Simon Conway-Morris came across a fossil with bizarre features. This was in the Burgess Shale in the Canadian Rockies.

The British Paleontologist Simon Conway discovered the animal was classified as a worm. He had a different opinion. The fossils he found indicated that the animal must have moved around with seven pairs of stilt-like spines. And it must have had seven tentacles waving on its back. He named it Hallucigenia. This name was because of its weird and dream-like features.

However, there were a lot of controversies about this model till 1991. Lars Ramskold and Hou Xianguang discovered fossils of the Hallucigenia in China. 

They clarified that Conway-Morris described the Hallucigenia upside-down. So, it was flipped because of its relation to the Microdictyon. Instead of spines, the Microdictyon had plates on their backs. This feature made it easier to understand the function of the ‘tentacles’ described by Conway. The ‘tentacles’ were the organism’s legs.

However, one mystery remains unsolved— Where was the Hallucigenia’s head? Conway-Morris described the head as the blob-like structure at one end of the Burgess Shale fossil. But Ramskold, in 1992, speculated that the blob might be a dead stain. There was no conclusive evidence to validate both suggestions. 

In the mid-2010s, when the preserved fossil was put under the electron microscope, the mystery was resolved. Scientists were not only able to recognize the head of the organism. They could recognize other head details like a pair of simple eyes, and teeth around its mouth.

canadian rockies

The Burgess Shale in the Canadian Rockies is where a lot of fossils are discovered, including that of the Hallucigenia.


Extinction- When Did It Die

The Hallucigenia was one of the many species that lived about 500-504 million years ago during the Cambrian explosion.

Hallucigenia was one of the species that went extinct due to the Late Ordovician Mass Extinction event. The Ordovician-Silurian extinction event occurred about 443 million years ago. This phenomenon was the first of the big five major extinction events in earth’s history.

The Ordovician-Silurian extinction event was the second largest extinction event. It eliminated 49-60% of marine genera and about 85% of marine species. The Hallucigenia genus was included as well. However, this event presented no major changes in the ecosystem, nor did it lead to morphological innovations.

Similar Animals to the Halluciginea

The Hallucigenia was not the only walking worm to ever exist. There are other similar panarthropoda species like the Hallucigenia. We have:

  • Antarctic Scale Worm: With the species name Eulagisca gigantea. It is a scale worm found in Antarctica. It is also found at 40m to 700m of the southern ocean depths. It is scientific name is in respect to its gigantic size in comparison to other marine worms
  • Caterpillar: This is a general name for the feeding stage of organisms with a complete life cycle, mostly butterflies. The caterpillar can be an aquatic or a terrestrial animal. It can be hairy, spiky, and poisonous. The caterpillar is a voracious feeder. It is an herbivore and feeds primarily on leaves. It can also feed on other plant parts like seeds or flowers.


The Hallucigenia was a bizarre walking worm that confused the early scientists who discovered it. The Ordovician-Silurian event brought the end of this genus. But recent studies show that the weird creature might be linked to a modern group of animals like the rainforest velvet worms.

Up Next: Discover more secrets evolution has to offer. Understanding what ancient animals have existed helps to appreciate today’s ecosystem better. We offer more articles on ancient animals and events on this site.

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About the Author

Growing up in rural New England on a small scale farm gave me a lifelong passion for animals. I love learning about new wild animal species, habitats, animal evolutions, dogs, cats, and more. I've always been surrounded by pets and believe the best dog and best cat products are important to keeping our animals happy and healthy. It's my mission to help you learn more about wild animals, and how to care for your pets better with carefully reviewed products.

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