An international team of scientists have unearthed the fossil remains of an ancient species of tongue worm believed to be 425 million years old. The parasite was discovered at a site in Herefordshire, England still attached to its animal host.

David Siveter, a professor at the University of Leicester and one of the researchers, said a volcanic eruption had killed and preserved the parasite along with other marine animals found at the site.

The researchers gave the creature the name Invavita piratica, which means "piracy" or "ancient intruder." They said it is the first adult tongue worm to be discovered in the fossil record.

The tongue worm is believed to be the ancestor of 140 species of present-day parasites that can be found in the respiratory systems of other creatures.

"In fact, it's not a worm," Siveter said. "It belongs to the broad group of animals we call arthropods."

Arthropods are known to be a very large animal group that includes crustaceans, arachnids and insects.

To find out what the ancient parasite looked like, the team conducted a CT scan of the fossil then created a three-dimensional image of the tongue worm. However, the original specimen was destroyed during the process.

Siveter explained that the fossil and the rock it was set on had the same composition, making it difficult to produce the virtual 3D image without grinding away at the layers of the specimen.

The reconstructed image showed that the tongue worm had a worm-like body with a head and two pairs of limbs.

Through the help of the 3D image, the researchers were able to have a better understanding on how the creature came to be.

"Most modern tongue worms infect vertebrates - including humans - but what we have is a tongue worm that infested an invertebrate [marine] animal," Siveter said.

"So it's telling us about the origin of their lifestyle - how they moved from a water-based environment to a land-based environment."

While the scientists refuse to disclose where the fossil was exactly found in order to protect it, Siveter said the site is a "treasure trove" of biological information.

The findings of the research are published in the journal Current Biology.