Oh This Old Thing? It's Just a Three-Foot-Long Shipworm

The shells of a mysterious, three-foot-long shipworm species were first documented in the late 1700s, but the worm always managed to stay more or less out of the spotlight, and has largely avoided being researched. Now, scientists have tracked down, dissected, and researched the elusive shipworm, which has been chilling in the Philippines all this time.

Video: Margo Haygood

"We've known about these creatures a long time," Daniel Distel, the research professor and the executive director of Ocean Genome Legacy, a marine research organization at Northeastern University in Boston, said in a phone interview. He's the co-author of a new paper describing the shipworm, in the journal Proceedings of the National Academy of Sciences. "I've been looking for them for about 20 years. It was pretty crazy the first time we saw them." The Kuphus polythalamia that Distel and other scientists found and studied spends its days in a log storage pond in Mindanao, surrounded by the smell of rotten eggs. This is because the organic-rich mud it lives in emits hydrogen sulphide, which the shipworm (a type of saltwater clam) consumes to survive—unlike other shipworms, which munch on wood.

Distel and his collaborators started chasing this species after a documentary that showed a patch of K. polythalamia shells aired on Philippine television, giving them a useful hint about where to find them.

Senior author Margo Haygood was in the lab the first time a live K. polythalamia, in excellent condition, was dissected in 2011. (They've been studying them since.) She was recording the whole thing.

"It was amazing to see how powerful and alive they were," Haygood, a research professor at the University of Utah, said. "You can see Dan Distel pull out what looks like this tube, and it just keeps coming and coming because these are such large animals."

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Haygood said the team was initially struck by how the animal managed to feed. The end of the shell, which houses the animal's mouth, is closed—suggesting they weren't using their mouths to eat.

"The answer, at the end of years of work, is that (K. polythalamia) have bacteria living inside of them that are producing their food for them," she said. "We don't know how the sulphide, the gas that presumably dissolves in the seawater, gets into the animal."

The team discovered that this shipworm lives on a diet of hydrogen sulphide and carbon dioxide, Distel said. In order to do that, the K. polythalamia needs to have sulfur oxidizing chemoautotrophic (obtaining energy from inorganic chemicals) bacteria in its gills. Currently, the researchers only know about this one population of K. polythalamia, but Haygood said the shells are collected from a variety of locations in the Philippines and elsewhere in the Indo-West Pacific, suggesting there are more out there to find. And plenty of questions, too.

"Do they live in mud even as juveniles or do they start out living in wood and then jump to living in the mud?" she said. "How fast do they grow? When we get one of these animals that's over a metre long, is that five years old, or 100 years old?"

These researchers also want to learn more about the K. polythalamia habitat. Most animals that live in similar habitats are very small, according to Distel, nothing like a K. polythalamia, which averages about the size of a baseball bat but can grow bigger. "I'm five-foot-three and I've seen a prize specimen in a private shell collection longer than I am tall," Haygood said.

According to her, this discovery has yielded decades' worth of study.

Until then, happy swimming!

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