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Giant Tube Worm: Riftia pachyptila
In 1977 geologist John “Jack” Corliss led an expedition, sponsored by the Woods Hole Oceanographic Institute and the National Science Foundation, to the Galápagos Rift. The rift, located some 400 kilometers (250 miles) to the north of the Galápagos Islands, is where two of the earth’s tectonic plates meet. Venturing 2,400 meters (8,000 feet) down in Alvin, the first manned deep-sea submersible, these scientists were trying to determine whether hydrothermal vents existed on the ocean floor. They knew that there were lots of underwater volcanoes, but no one had ever seen a deep-sea hot spring. What they discovered, ultimately, was utterly unexpected, and did nothing less than change our understanding of life on the planet. These geologists—there were no biologists on this expedition—found life at the very bottom of the ocean, in the darkness, miles from the sun. “We all started jumping up and down,” John Edmond, another geologist on the trip, said. “It was a discovery cruise. It was like Columbus.” Nestled around the near-boiling water of the Rift’s hot vents, they found communities of foot-long clams, white crabs, and giant white tube worms with bright red plumes waving in the current—all species that had never been seen before.
Although the expedition was hardly equipped to handle biological life, the team managed to collect samples of these animals—and they sent the worm to Dr. Meredith Jones, an invertebrate zoologist and head of the Division of Worms at the Smithsonian’s National Museum of Natural History.
Jones had studied other deep sea worms—now recognized as annelids of the family Siboglinidae—but this one was different than any other deep sea worm that had been discovered. To be sure, he visited the Galapagos Rift himself on an expedition in 1979 and collected several more specimens from a vent site called the Rose Garden—so named because of the cluster of red plumes of the worms.
In the lab, Jones and his fellow researchers made several exciting conclusions. First, the worm was a new species, which they named Riftia (Riftia pachyptila Jones) in 1981, in honor of its home at the Rift. Second, the worm specimens he collected ranged up to six feet long and more than an inch wide—exceedingly large compared to other known deep sea worm species, which typically measure less than one inch in length. Third and most puzzling, Riftia did not seem to have any mouth or a digestive tract! (Later, Jones and his co-workers would find that the larvae have a mouth and a gut, but that the mouth closes over and the gut-wall swells up so that all the space in the gut is lost.)
So how did these very large worms—living in absolute darkness at the Galápagos Rift, more than a mile and a half below the surface–feed? The answer was thrilling, and it revolutionized our understanding of how we define life. Jones and his colleagues found that the worms have evolved to use the heat of the Earth, escaping from hydrothermal vents, to generate their food. What was even more interesting was that the worms themselves don’t make the food. The bacteria living in their gut-wall do. Riftia use hemoglobin in their blood (like the hemoglobin in mammalian blood) to pick up a toxic gas called hydrogen sulfide, which is escaping from the hot vent. Bacteria break down the hydrogen sulfide to sulphur, thereby releasing energy—similar to what happens in photosynthesis, except that plants break down water instead. The bacteria use some energy to survive in Riftia, while Riftia use the rest of the energy transported in proteins and carbohydrates produced by the bacteria to make its own food. This process, called chemosynthesis, is considered one of the great scientific discoveries of the last century.
In 2002 to mark the 25th anniversary of the first trip to the Galápagos Rift and the discovery of life at the bottom of the sea, the National Oceanic and Atmospheric Administration (NOAA) undertook a new expedition to the area. They discovered that the Rose Garden site no longer exists, having apparently been covered by a lava flow sometime in the last ten years. Nearby, however, they found a new site, with tiny new hydrothermal animals, which they named Rosebud. Watch a video of life on the ocean floor from that expedition.
The National Museum of Natural History has the largest collection of Riftia in the world, which is used for research and educational purposes. The museum also still has the original specimen that was sent to Jones in 1977.
Visitors to the Museum don’t need to embark on a deep sea voyage to see Riftia’s bright red plumes extending from white tubes. A specimen that was collected from one of Jones’ trips to the gardens of the Galápagos Rift is currently on display in the Sant Ocean Hall.
Meredith Jones’ article “The Giant Tube Worms,” in Oceanus (Vol. 27, no. 3, fall 1984)
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