New insights into anatomy of ancient tentacled creature

Illustration of Cotyledion tylodes living as a group

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Scientists have shed light on a peculiar tentacled marine creature that lived 520 million years ago.

Experts thought that Cotyledion tylodes may have belonged to the jellyfish-like cnidarian group.

But new anatomical evidence from the animal's fossilised remains suggests the species was an early member of the group of small marine organisms called entoprocts.

The findings are published in the journal Scientific Reports.

Results of the study, by an international research team, suggest that entoprocts appeared earlier than previously thought.

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Entoprocts are small organisms that feed by straining food particles from water.

Scientists analysed hundreds of Cotyledion tylodes fossils preserved in the Chengjiang fossil site in Yunnan province, China, dating from the Cambrian geological period (545 to 495 million years ago).

To date, the only uncontested fossil entoproct comes from the Jurassic (205 to 142 million years ago).

However this reinterpretation of Cotyledion tylodes as an entoproct places the fossil record of this group in the earlier Cambrian period.

Some anatomical characteristics of Cotyledion tylodes are comparable to those of modern entoprocts, especially the presence of a U-shaped gut with a mouth and anus surrounded by a crown of tentacles.

"This is... the first time to confirm that [Cotyledion tylodes] had a U-shaped gut accommodated in the calyx cavity," said Zhifei Zhang, from Northwest University, Xi'an city, Shaanxi Province, China, who worked on the study.

Cotyledion tylodes fossil Cotyledion tylodes fossil from the Chengjiang site

The bizarre-looking creature also had a goblet-shaped body with an upper cup-like cavity and lower elongated stalk, with which it "attached to exoskeletons of other organisms", explained Mr Zhang.

Cotyledion tylodes was larger than extant entoprocts, measuring between 8mm and 56mm in height. Its body was covered in external, hardened structures called sclerites, which are not found on modern entoprocts.

Evolutionary big bang

The "Cambrian explosion" saw the relatively sudden appearance of abundant life forms in the sea.

Mr Zhang said that the team's reinterpretation of Cotyledion tylodes as belonging to the Entoprocta phylum adds further support to the idea that "nearly all the living phyla of animals suddenly appeared in the Cambrian".

However, few fossil representatives of Lophotrochozoa (the superphylum containing the entoprocts group of animals) have been found in Cambrian fossil records.

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