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Bizarre Evolutionary Twist to 'Bone-Eating' Worms

Dec 12, 2014 02:57 PM EST
Osedax priapus
Researchers have revealed a bizarre evolutionary twist to deep-sea "bone-eating" worms, an already unusual species, a new study says. [Pictured: A male Osedax priapus (bone worm) attached on a seal bone (scale: 0.5 mm).]

(Photo : Greg Rouse)

Researchers have revealed a bizarre evolutionary twist to deep-sea "bone-eating" worms, an already unusual species, a new study says.

Osedax were first discovered 12 years ago in the deep depths of the ocean, when researchers first noticed that the worms matured only in female form, with males living in a larval state within the females' bodies.

Not only that, but these "zombie worms," as they're sometimes called, also feast on the bones of dead animals.

And now to add to the strange saga of Osedax worms, new research shows that males of this newly discovered species grow to the same size as females, and go to great lengths to mate.

"This worm was weird enough as it was and now it's even weirder," study author Greg Rouse, a marine biologist at Scripps Institution of Oceanography, said in a statement.

Examining bone worms collected at 700 meters (2,296 feet) deep by an MBARI remotely operated vehicle, Rouse's team came upon this surprising new twist.

While females of the new species are roughly the same size as their previously studied relatives, the males on the other hand are tens of thousands of times larger than those of other Osedax worms.

"This case is exceptional because the genes for producing full-sized adult males should have deteriorated over time due to disuse," co-author Robert Vrijenhoek noted. "But apparently the genes are still there."

Normally, the females of these mouthless, gutless creatures contain harems of tiny dwarf males providing food to their tiny mates. But with the new species of mega males, which are roughly the same size as their female counterparts, they can feed on their own.

Researchers were also curious as to how the two mate, given that both the males and females are independent of one another. It turns out these guys are flexible - able to stretch to ten times their normal length in order to find a female to mate with.

For this reason they chose to name the new species Osedax "priapus," after the mythological Greek god of fertility.

"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," Rouse added.

The bone-eating worm is described in the journal Current Biology.

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