Bone-eating worms are mutating

Bone eating worm
Screen capture Scripps Oceanography

In the depths of the ocean, where the sun doesn't shine, bone-eating worms wait for a juicy carcass to sink to them. Scientists first stumbled upon them more than 12 years ago and are continuing to discover unusual things about these animals.

What makes these creatures unique is the dwarf males that form a harem. These males look like larvae and as many as 114 of them live inside the females. To mate, males ejaculate from their head and fertilize the female's eggs. What's left of the egg yolk provides food for the males swimming around her insides.

Marine biologist Greg Rouse commented that the bone-eating worms, named Osedax, are an “evolutionary oddity unlike any other in the animal kingdom."

And now, a new study on these deep sea creatures shows that just when we start to think we're getting the hang of evolution, it presents us with a new twist. A new species of Osedax has been discovered - and this time, the males are the same size as females. This presents scientists with a case of reverse evolution - where the males are returning to a state they were in long ago on the evolutionary path.

"Evolutionary reversals to ancestral states are very rare in the animal kingdom," study author Robert Vrijenhoek said in a press release. "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."

Like the females, the large males feast on bones. They have no mouth, anus or gut, so they absorb lipid reserves through their 'roots.' To get to these reserves they dissolve the bone with acid from these roots. In terms of mating, the males no longer have the same proximity to female Osedax as they did before. Now, they have to reach out for females by elongating themselves up to 10 times their size.

“This worm was weird enough as it was and now it’s even weirder,” Rouse told “This shows us that there continue to be mysteries in the sea and there is still so much more to discover, especially since we only found these creatures 12 years ago.”

Bone-eating worms are mutating
This might be the most bizarre creature in the world.