Weird new species of deep-sea worm found in Monterey Bay

A weird new species of deep-sea worms that live on the rotting bones of dead animals on the ocean floor have reversed their own course of evolution unlike any others known in the animal kingdom, scientists report. The males of these bizarre creatures have become immensely larger than their own diminutive tribal forebears, and they mate in fashions vastly different than their closest relatives, the researchers say. The little worms were discovered thriving on the decaying bones of a long-drowned seal nearly 3,000 feet deep at the bottom of Monterey Bay, in the same area where an equally strange species of worm was found a dozen years ago by a team from the Monterey Bay Aquarium Research Institute, or MBARI. Where Darwin once noted that in most animals sexual selection drives males and females to be different, the genes of these tiny male worms have abruptly made them equal in size to the females in the age-old Darwinian competition for food and sex. The worms were discovered by marine biologist Greg Rouse of the Scripps Institution of Oceanography during expeditions above the mile-deep Monterey Canyon and off the Oregon coast aboard the research vessel Western Flyer, led by MBARI’s evolutionary biologist Robert Vrijenhoek. The species is called Osedax priapus after the mythological god of fertility because the 3-inch-long males have been observed extending their eyeless bodies far out to hunt for females to mate. Osedax means “bone devourer.” Vrijenhoek discovered the first known species of the Osedax worms in 2002, and noted they had no mouth, no stomach, no legs and no eyes. But the body of each red-crested female held hundreds of males so tiny they looked like larvae barely visible in the microscope and they subsisted only on tiny scraps of yolk from the thousands of eggs that each female carried inside her body. The newly discovered worms are an “evolutionary oddity unlike any other in the animal kingdom,” Rouse said. The tiny dwarf males are now tens of thousands of times larger than the other species, and are just as large as the females, he said. And the males that once fed only on scraps inside the females are now consuming the same rotting bone as the females. “This case is exceptional because the genes for producing full-size adult males should have deteriorated over time because they weren’t used by the dwarf males,” Vrijenhoek said. “But apparently the genes are still there. “And although those microscopic dwarf males weren’t competing with the females for food, in this much larger species they do,” Vrijenhoek said in an interview. “So it’s our hypothesis that here there’s a new potential for sexual conflict, and the ability of the males to stretch themselves out like rubber bands to roam for females suggests that they’ve reinvented mating. “It’s a throwback to an earlier ancestral species more than 40 million years ago,” he said. “We’re continuing to collect more species to see what their genes are telling us.” By now more than 20 species of the annelid worms have been found. The scientists have reported on the new species of annelid worms in the journal Current Biology. David Perlman is The San Francisco Chronicle science editor. E-mail: dperlman@sfchronicle.com