Ancient tube worm was ‘underwater architect’

An analysis of ancient sea worm fossils has rewritten what we though we knew about life on the ocean floor, according to a new report in the journal BMC Biology.

In the study, a team of researchers from Canada and the United Kingdom analyzed tube-like fossils that served as the home of the Oesia, sea worm that lived on the floor of the ocean around 500 million years ago. The strange fossils were originally thought to have come from a type of seaweed called Margaretia.

The analysis confirmed Oesia is from a class of creatures known as hemichordates. These are part of a bigger group known as deuterostomes, with humans and other vertebrates as members. By learning more around these early creatures, scientists hope ultimately to be able to identify and describe a remote ancestor common to all deuterostomes.

“Hemichordates are central to our understanding of how deuterostomes evolved,” study author Karma Nanglu, from the University of Toronto, said in a news release. “Through them, we can get clues about the anatomy and lifestyle of the last common ancestor that we all share, and this adds further evidence to the hypothesis that the ancestor was a filter-feeder like Oesia.”

New Findings about Ancient Ancestor

The new study props up the common view this ancestor was a “filter feeder”, which ate by drawing in water and straining out sustenance. Oesia had gills down the majority of its body to discharge water afterwards, and openings in the walls of its tubular residence to let the water out and in.

Study author Christopher B. Cameron, associate professor of marine biology at the Université de Montréal noted that Oesia appears to be very similar to acorn worms, which live at the bottom of the sea today.

“Acorn worms are notoriously sparse in the fossil record,” he said. “Only a handful of fossil species have been described, making the recognition of such an ancient representative of the group particularly noteworthy.”

The fossils in the study, and others like them, had been classified as the seaweed Margaretia since the 1920s. However, the new research makes it clear that these were structure that Oesia inhabited and not a type of seaweed. The tubes grew to nearly 20 inches in height and were sealed off at both ends.

“Only single worms are found within tubes, suggesting a solitary mode of life,” Nanglu said. “This gives Oesia an interesting mix of characteristics: it has the general appearance and solitary lifestyle of the modern acorn worms, but the tube dwelling lifestyle and posterior attachment structure shown by their closely related sister-group the pterobranchs.”

Fossils indicate acorn worms eventually left these tubes for a life in sediments along the seabed.

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Image credit: University of Toronto

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