With five eyes and a vacuum-hose face, Opabinia defied all known animal classification.

Nature · Published 3 October 2026 Swipe more like this →

In short: When paleontologists first presented a detailed reconstruction of the 505-million-year-old Opabinia regalis in 1975, the audience laughed. This bizarre, soft-bodied creature from the Burgess Shale possessed five eyes, a backwards-facing mouth, and a flexible, clawed proboscis. It remains one of the most enigmatic figures in the history of evolutionary biology.

Discovered in the Burgess Shale of British Columbia, Opabinia regalis lived during the Middle Cambrian. Measuring up to 7 centimeters, the animal featured a segmented trunk with lateral flaps and a fan-shaped tail. Its most striking feature was a hollow, striated proboscis that projected from beneath its head, likely used to forage for small, soft food on the seafloor. Because the animal lacked mineralized armor, its body was flattened during fossilization, leaving researchers to debate the function of its internal structures for decades.

The classification of Opabinia was a subject of intense 20th-century debate. Original describer Charles Doolittle Walcott initially classified it as a crustacean in 1912. By 1975, Harry B. Whittington argued it was not an arthropod at all, suggesting it represented an ancestral stock for annelids and arthropods. However, modern consensus now places Opabinia as a basal stem-group arthropod, closely related to radiodonts like Anomalocaris and various gilled lobopodians. This shift in understanding was aided by the discovery of similar fossils, such as the 2022 identification of Utaurora comosa in Utah.

Opabinia became a focal point in the debate over the Cambrian explosion. Early researchers like Preston Cloud viewed the rapid appearance of complex life as an explosive, unique event, a sentiment echoed by Stephen Jay Gould, who once considered titling his book on the Burgess Shale 'Homage to Opabinia.' Today, the development of 'stem group' theory—which categorizes extinct relatives of living lineages—allows scientists to explain these strange organisms through standard evolutionary processes rather than assuming unknown mechanisms. While Opabinia once seemed like a failed experiment, it is now recognized as a vital piece of the arthropod evolutionary puzzle.

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