Bizarre deep-sea worms that can devour a whale carcass by dissolving it, already unique because males live their entire lives inside the bodies of female worms, have just gotten even weirder, researchers say.
Bone worms, given the nickname "zombie worms," are some of the oddest creatures found in the deep ocean.
Possessing neither mouth nor gut, they can consume a whale carcass -- bones and all -- using a structure similar to what's found in a human kidney to dissolve the carcass and absorb nutrients in contains.
In all the species of bone worms found up to now, females possess "harems" of tine larval males within their bodies that the provide with food.
Now, however, researchers have identified a new species of bone worm where the males have "escaped" that evolutionary confinement to grow as large as the females and are capable of feeding on their own.
It's a rare case of evolutionary reversal that has seen the males retain the genes allowing them to grow to full size.
"This worm was weird enough as it was and now it's even weirder," says study author Greg Rouse, a marine biologist at Scripps Institution of Oceanography in California. "This shows us that there continue to be mysteries in the sea and there is still so much more to discover."
Rouse and his research colleagues, writing in the journal Current Biology, called the discovery of a new species of Osedax bone worms unexpected.
"It's the first known example of such a dramatic evolutionary reversal from dwarf males," Rouse says.
The new species with its full-size males was discovered 2,296 feet below the ocean by a remotely operated vehicle of the Monterey Bay Aquarium Research Institute.
"Evolutionary reversals to ancestral states are very rare in the animal kingdom," says study coauthor and MBARI researcher Robert Vrijenhoek. "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."
In other Osedax species the dwarf males remain attached within their female hosts so mating does not require that they have the power of movement.
Males in the newly discovered species have evolved an unusual technique for mating with the separate females, the researchers found.
"The evolutionary solution (the new species) found was to actually make the male's body very extendable so he can reach far out to find females to mate with -- he can extend his body ten times its contracted state," Rouse says.
The male's body has essentially evolved to be a single-purpose tool for accomplishing mating, he says, "and that's why we named it Osedax 'priapus,' the mythological god of fertility."