northSome of the deepest hydrothermal vents in the Pacific lie early 13,000 feet (4,000 meters) underwater in the Pescadero Basin of the Gulf of California, and they are covered in tiny iridescent worms. “You’ll see little bright pink, blue, red, black and white worms,” says Avery Hiley, a graduate researcher at the Scripps Institution of Oceanography in San Diego.
These are hungry scale worms, or Peinaleopolynoe – comb our hair meaning “hungry” or “famous” in Greek, so named because they were first found clustered around a pile of food that scientists had experimentally left on the deep sea floor. For years they have been nicknamed “Elvis worms” for their shiny scales, reminiscent of the sequined jumpsuits Elvis Presley wore.
There are six known species of hungry scale worms, all about the size of a thumb and living in the deep sea, including four appointed in 2020. One of these, which features a cape of bright pink scales, is specifically named after the king of rock and roll: Hiley and his colleagues named it Peinaleopolynoe elvisi.
Hungry worms have been found on the carcasses of dead whales and on volcanic seamounts, hydrothermal vents and cold seeps, where methane seeps through the seafloor like champagne bubbles.
The worms likely feed on bacteria that take advantage of the chemicals that grow in all of these habitats. “They have mandibles that we suspect they use to brush against bacteria,” says Hiley. “So we think they are bacteriovores.”
When Hiley and his colleagues carried out genetic testing of hungry scale worms from the Pescadero Basin, what they assumed were multiple species, each with its own color, turned out to be a single species. “We realized that with age it seems that [the] the species changes color as it develops from a juvenile to an adult form.”
The colors of the worms are not created by pigments but by light reflecting and refracting within the internal structure of the scales, in the same way as with the bright blue wings of butterflies. The only light available in the deep sea to make them glow is the bioluminescence of other animals, but they glow brightly in the light of the headlights of robots and submersibles diving into the depths.
It’s possible that as the worms age, their color changes because their scales get thicker, altering the way light passes through them. The thickest scales are blue. Slightly thinner they are pink. “The smaller worms tend to always be white and the scales are very fragile,” says Hiley.
Previously, when scientists collected hungry scaleworm specimens, many had splinters in their thick scales; they assumed its scales were damaged when a deep-diving robot picked them up and transferred them to the surface. Then, in 2017 in the Pescadero Basin, a rare scene was caught on camera. “It turns out that this species actually does this fighting ritual,” says Hiley.
Hungry scale worms bounce on the spot and pummel each other, inverting their snouts and biting each other to pieces with their powerful jaws. “It was a piece of the puzzle that we didn’t know about for a long time,” says Hiley.
It is still not clear why the worms fight each other. “We definitely have more observations to make,” she says.
Another puzzle Hiley wants to solve is how hungry worms evolved from ancestors that lived in shallow seas in order to survive in the hyper-pressurized, oxygen-poor environment of the deep sea. She is looking for clues in her genes.
“We’re starting to see some weird things at the genetic level with these deep-sea worms,” says Hiley. The 29 species of deep-sea scale worms, including the hungry species, have a large variation in their gene order compared to worm species that live in shallow seas. Hiley is investigating whether this can go some way to explaining how the worms have adapted to the rigors of the deep ocean.