An artist's impression of what Orthrozanclus elongata might have looked like in life. [Photo provided to China Daily]

Archaeologists in China have discovered a fossilized sea creature that they describe as "strange beyond measure", with long spines along its wormlike body and a shell that covers its head like a helmet.

The 515-million-year-old specimen was unearthed last year by a fossil collector in the hills of the Maotianshan Shales, an archaeological hot spot in Yunnan province.

The collector gave the fossil to Zhao Fangchen, a paleobiologist at the Chinese Academy of Sciences, who studied it with researchers from Durham University in the United Kingdom.

"The creature is like a mythical beast," Martin Smith, an assistant professor at Durham, told science news website Live Science.

He said researchers were surprised by the creature's unusual anatomy, which had spines like cocktail sticks "that emerge from its sides" and a "head covered by a small shell, almost as if it's wearing a bike helmet".

"We don't know much about the animal underneath these mineralized plates－whether it had legs or a sluglike foot, or whether it had teeth or tentacles," Smith added.

He said the fossil is "incredibly rare", with only two specimens having been found among the tens of thousands of creatures seen in the same deposits.

The 2-centimeter-long creature, whose scientific name is Orthrozanclus elongata, lived during the Cambrian period, a time before life had colonized dry land. Microscopic plants, microbial mats and invertebrates with exoskeletons, including trilobites and arthropods, were the dominant forms of marine life.

In the study of the creature published in the journal Scientific Reports, the authors said Orthrozanclus elongata may provide clues about the evolution of mollusks. The creature, which appeared to be mobile, could be an ancestor of some of today's brachiopods, which live in shells and are largely sedentary, it said.

"Whereas many linages show evolutionary trends toward greater activity and complexity, brachiopods seem to have settled down to a sedentary existence, like a retiree settling down in a favorite armchair," Smith said.