Hallucigenia was not an arthropod. It did not have jointed legs or a segmented body covered in a hard exoskeleton.
However scientists have had a difficult time figuring out exactly what it was. In the 1990s, after studying newly discovered fossils, scientists finally identified Hallucigenia as a close relative of a rare modern animal known as an onychophoran. Onychophorans are probably closely related to arthropods.
Long live the onychophoran
If the hypothesis that Hallucigenia was an onychophoran is correct, it means that Hallucigenia‘s lineage is a long-lived one. Oncychophorans have weathered all of Earth’s mass extinctions, but they have never become a very diverse group — there are fewer than 100 species of onychophoran alive today.