Four new deep-sea worm species discovered

Genetic analysis correctly pinpoints species on the tree of life

Date: February 3, 2016

Source: University of California - San Diego

A pink flatworm-like animal known by a single species found in waters off Sweden has puzzled biologists for nearly six decades. New discoveries half a world away by a team of scientists from Scripps Institution of Oceanography at UC San Diego, the Western Australian Museum, and the Monterey Bay Aquarium Research Institute (MBARI) have helped properly identify these elusive creatures through genetic analysis.

In the Feb. 4 issue of the journal Nature, the researchers describe four newly discovered species living near deep-sea cold seeps, hydrothermal vents, and whale carcasses off the coasts of California and Mexico. The new discoveries have allowed the scientists to finally stabilize the placement of the five species, all in the genus Xenoturbella, on the animal tree of life.

The 10-centimeter (4-inch) long Xenoturbella churro, named for its resemblance to the popular fried-dough pastry, is one of four species recently discovered that lie near the base of the evolutionary tree of animals. It was found in a 1,700-meter (5,577-foot)-deep cold seep in the Gulf of California.

"The findings have implications for how we understand animal evolution," said Scripps marine biologist Greg Rouse, the lead author of the study. "By placing Xenoturbella properly in the tree of life we can better understand early animal evolution."

The animal's shifting position on the tree of life began when the first species, named Xenoturbella bocki, was found off the coast of Sweden in 1950. It was classified as a flatworm, then, in the 1990s as a simplified mollusk. In recent years, Xenoturbella has been regarded as either close to vertebrates and echinoderms, or as a more distant relative on its own branch further away. Knowing where Xenoturbella belongs is important to understand the evolution of organ systems, such as guts, brains and kidneys, in animals.

"When Greg first spotted the worms gliding through a clam field in Monterey Bay, we jokingly called them purple socks," said MBARI scientist Robert Vrijenhoek, a co-author of the study who led the deep-sea expeditions using remotely operated vehicles.

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