The examination of ancient fossils by leading researchers at a North East university and from across the globe has uncovered new facts about the evolution of the sea worm. 

Boffins from Durham University have shed light on the evolution of annelid sea worms - Iotuba chengjiangensis - using fossilised remain that showed their internal makeup. These 15 fossils showed details of the structure of their guts and kidneys. 

By collaborating with scientists from Northwest University, Xi'an, China, academics from Durham Univerity's Earth Sciences department found that annelids – or segmented worms – diversified into different lineages some 200 million years earlier than previously thought. 

This means the annelids were part of the evolutionary leap known as the Cambrian explosion, which saw a huge rise in species between 540 and 530 million years ago.

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The Cambrian explosion is demonstrated by fossil records and saw the appearance of many of the major groups that make up animal life on earth today.

Study co-author Dr Martin R. Smith, in the Department of Earth Sciences, Durham University, said: “We know that the main animal lines we see today emerged during the Cambrian explosion, but we always thought annelid worms were late to the party, and their major subgroups didn’t begin to diversify until nearly 200 million years later.

“But the amazingly preserved fossils we have studied and the structure of these amazing little creatures challenge this picture, and show that annelid worms – including Iotuba chengjiangensis – seemed to follow the pattern of events initiated by the Cambrian explosion.

The Northern Echo: Artist's reconstruction of Iotuba, showing front of body with everted head (with branchial filaments and mouth) surrounded by cage of spines (chaetae).Artist's reconstruction of Iotuba, showing front of body with everted head (with branchial filaments and mouth) surrounded by cage of spines (chaetae). (Image: Durham University)

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“Detailed fossils of this type of worm are extremely rare, so it was great to be able to study the fossilised record of this tiny animal in such detail.

“It turns out they weren’t late to the party at all, they were just hiding in a side room.”

Research lead author Dr Zhifei Zhang, Northwest University, Xi'an, China said: “Annelids are one of the largest and most successful phyla of animals that are flourishing in both terrestrial and marine ecosystems with the most diversified living lineage, Polychaeta, living in the sea.

"The most well-known are, for example, earthworms, leeches and clam worms. There are also at least 20,000 species and 80 families of Polychaete in the modern sea.

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“However, their earliest geological records of fossils in Cambrian deposits, even in the well-known Konservat-Lagerstätten are quite rare.

“Is this because the delicate worms didn’t exist, or simply didn’t preserve? Our research gives the first insightful answer: biodiversification of the segmented worms occurs much earlier than thought before.”

The research was funded by the National Natural Science Foundation of China and the Changjiang Scholars Program of the Chinese Ministry of Education.

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