Scientists find giant, elusive clam known as ‘the unicorn of mollusks’

The giant shipworm.Marvin Altamia

For mollusk mavens, it was like finding a unicorn — only this elusive creature burrows in the mud, loves rotting wood, and is not featured in any bedtime stories or rainbow-colored posters in your child’s bedroom.

Considered the world’s longest bivalve, the giant shipworm has been known to scientists for more than two centuries, but only from samples of its white, tusk-like shell and fragments of its slug-like body preserved in jars.

No living scientist had ever laid eyes on one in the wild, or knew where to find one of the slimy specimens, which can grow up to 5 feet in length.

Now, an international team of scientists — including a mollusk researcher from Northeastern University — has announced that giant shipworms have been located, alive and in the flesh, in a saltwater lagoon in the Philippines.

“For me, it is like a finding a mythical creature,” said Daniel L. Distel, a research professor at Northeastern, who has been studying mollusks since the late 1980s and had long dreamed of finding a giant shipworm. “You know it’s something no one has ever seen. It’s like coming across a living dinosaur.”

Gonzalo Giribet, a professor of organismic and evolutionary biology at Harvard, who was not involved in the hunt, likened it to the discovery of the coelacanth, the prehistoric fish that was long thought to be extinct until it was located in a fish market in South Africa in 1938.

“It’s very exciting,” he said. “When things are known only by shells, you don’t know if some of these things have gone extinct already.”

In a thoroughly modern twist on the age-old hunt for rare creatures, the first break in the search for the giant shipworm came from a student at the University of the Philippines who was looking on YouTube, Distel said. The student, Distel said, happened upon a video of a Philippine news program that showed giant shipworms growing like carrots in a shallow lagoon.

“The miracle of social media,” Distel said. “It’s amazing.”

Working with colleagues in the Philippines, he managed to get his hands on one of the enigmatic mollusks, formally called the Kuphus polythalamia.

In video footage of the moment of truth, Distel can be seen carefully pulling the long, white shell from a tube filled with water and then cutting a round opening at the top, as his colleagues gather around him. Distel gently shakes the shell, and the slippery, jet-black body of the giant shipworm slides out. The first surprise, he said, was the color: most shipworms are tan or white.

“You know, I was pretty excited,” Distel said. “I was also a little bit nervous because this is such a rare animal and, here I was, about to dissect it and everybody expected me to know what to do.”

The encounter also made him miss Ruth D. Turner, a Harvard professor and leading expert in shipworms who died in 2000.

“Boy, if only Ruth could have seen this,” he recalled thinking as he examined the giant shipworm for the first time. “We used to scheme about trying to fund a trip to look for these things.”

Marvin Altamia, a researcher at the marine sciences institute at the University of the Philippines, was with Distel in the lab that day.

“I was awestruck when I first saw the sheer immensity of this bizarre animal,” he said in a statement released by the University of Utah.

“Being present for the first encounter of an animal like this is the closest I will ever get to being a 19th-century naturalist,” said another colleague, Margo Haygood, a research professor at the University of Utah College of Pharmacy, who was senior author of the paper that the team published in the April 17 issue of the Proceedings of the National Academy of Sciences.

The paper explains that the giant shipworm is remarkable not only because it was so elusive, but because of the way it eats.

Most shipworms, Distel said, use bacteria in their gills to feed off wood; in olden days, they were known to burrow into the hulls of wooden ships, hence their name. But giant shipworms live in marine sediment. Their bacteria use the gas from rotting wood as energy to produce carbon that nourishes the animal.

The process is similar to the one that allows animals to survive near deep-sea hydrothermal vents, he said.

In Distel’s lab, he keeps one of the giant shipworm shells displayed in a case designed for a commemorative baseball bat.

Distel, who is director of Ocean Genome Legacy, a nonprofit that preserves the DNA of marine species and makes it available for research, said the discovery points to the importance of studying ocean life, before it is further threatened by climate change.

“The ocean is full of things that remain to be discovered,” Distel said. “This is just scratching the surface of the weird creatures that are out there.”