Five years after discovering some of the strangest creatures in the world – mouthless worms that live in the bones of dead whales – scientists have taken a peek into their genes. Though not complete, the glimpse shows these creatures to be far more complicated than was known.

The worms, found in a gray whale skeleton off the coast of California, prompted scientists to designate them as representatives of an entirely new genus, dubbed Osedax. They belonged to a taxonomic family of marine worms that lack mouths and anuses, and rely entirely on bacteria to absorb and excrete nutrients. But Osedax was unique: Adult males were extremely small, and lived in colonies inside the females. Even more strikingly, they occupied an evolutionary niche comprised entirely of fallen whales.

"Picture the bottom of the ocean. Anything below 1000 meters is fed entirely by 'marine snow' — the things that are supported by photosynthesis at the top of the ocean, and the things that eat them, and eventually fall to the ocean floor," said Robert Vrijenhoek, a senior scientist at the Monterey Bay Aquarium Research Institute. "When a whale drops into your neighborhood, it's roughly equivalent to 2000 years of marine snow falling in a millisecond."

Since the discovery by Vrijenhoek and other MBARI researchers of Osedax, other species have been found in whalebones off the coast of Sweden and Japan. (Some of their names hint at the genus' weirdness: Osedax mucofloris roughly translates to "bone-eater snot-flower," in honor of its appearance.) A total of five species have now been named, enough for a comparison of their genetic characteristics to provide insight into their evolutionary history.

In a study published Tuesday in BMC Biology, Vrijenhoek looked for similarities and differences in five genes across the species. In much the same way that comparing genes from humans and Neanderthals would hint at the existence of other members of the Homo genus, the analysis suggested at least 12 more as-yet-unidentified lineages of Osedax. The worms might still be out there, though some may have gone extinct. It's believed that modern whaling, which drove many whale species to the brink of extinction, may have had equally profound effects on Osedax.

The genetic results also raise the question of just how long the whalebone-eating worms have existed. The five species appear to have shared a common ancestor at least 45 million years ago, when whales arose and diversified. But Osedax might have emerged even earlier, during the Cretaceous, and moved to whales when marine dinosaurs died out.

To figure that out, scientists will need to look for traces of Osedax in the fossils of dinosaurs and early whales. In the meantime, Vrijenhoek and others are learning more about how the worms live now. Since whale carcasses are hard to come by, the researchers have lured them with carcasses of other animals.

"The worms can live perfectly happily on cowbones," said Vrijenhoek. "We've also put down sea lion bones and pig bones. The worms don't seem to care."

Images: 1) MBARI. 2) University of Copenhagen. To see Osedax in real-time, visit the Monterey Bay Aquarium Research Institute's ocean-floor webcam, near which the researchers recently sank a pig.

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Citation: "A remarkable diversity of bone-eating worms (Osedax; Siboglinidae; Annelida)." By Robert C. Vrijenhoek, Shannon B. Johnson and Greg W. Rouse. BMC Biology, Vol. 7, No. 74, published online November 10, 2009.

Brandon Keim's Twitter stream and reportorial outtakes; Wired Science on Twitter. Brandon is currently working on a book about ecosystem and planetary tipping points.