Updated 10:35 AM EDT, Thu, Apr 18, 2019

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Deep Sea Zombie Worms that Eat People Evolve a New Species

Bone worms

(Photo : Norio Miyamoto/Naturwissenschaften) "Zombie worms" of the deep ocean have gotten weirder with discovery of new species of males.

Deep-sea worms called bone worms are the vultures of the ocean. They eat dead animals and people but have neither a mouth nor gut to digest their meals.

What's more, these bone worms, otherwise known to scientists as "zombie worms," were once thought to be a species dominated by females. The males' sole reason for existence was to feed the females and mate with them. They live their entire lives inside the bodies of female worms.

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A new study shows the male bone worms seem to have broken free of their bondage to the females and evolved into a new species.

Researchers have identified a new species of male bone worm that "escaped" this evolutionary confinement inside females and have grown as large as the females. More interestingly, this new male species can feed on its own.

Researchers said it's a rare case of evolutionary reversal where males retained the genes allowing them to grow to full size.

"This worm was weird enough as it was and now it's even weirder," said Greg Rouse, a marine biologist at Scripps Institution of Oceanography in California and study author. "This shows us that there continue to be mysteries in the sea and there is still so much more to discover."

Female bone worms have "harems" of tiny larvae males within their bodies that supply them with food. It is these smaller males that consume the bones and meat of dead animals and people using a structure to dissolve the carcass and absorb the nutrients in contains.

Researchers discovered the full-size bone worm males at an ocean depth of 2,296 feet using a remotely operated vehicle of the Monterey Bay Aquarium Research Institute.

"Evolutionary reversals to ancestral states are very rare in the animal kingdom. This case is exceptional because the genes for producing full-sized adult males should have deteriorated over time due to disuse. But apparently the genes are still there," says study co-author and MBARI researcher Robert Vrijenhoek.

Males in the newly discovered species have evolved an unusual technique for mating with the separate females, the researchers found.

The new male species can extend their body 10 times its contracted state to reach the females and mate with them, according to Rouse.

The male's body has evolved into a single-purpose tool for mating, he says, "and that's why we named it Osedax 'priapus,' the mythological god of fertility."

More than 20 species of the annelid worms have been found. The discovery on the new species of annelid worms was published in the journal, Current Biology.

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