New Shipworm Eats Stone

As alluded to by its name, most shipworms bore into and digest wood – making them a natural nemesis to docks, pier infrastructure, wooden vessels and sailors alike. The mollusks digest the wood with the help of symbiotic bacteria that live in their gills, a process which may help in the development of new antibiotics and bio-fuels.

Wednesday, a team of scientists unveiled a new, very different species of shipworm – whose taste for rock sets the bivalve apart from thousands of others. Although other animals burrow in stone, this new species, Lithoredo abatanica, is unique in that it actually eats the rock as it burrows, expelling sand as feces.

Lithoredo abatanica. Credit: Marvin A. Altamia and Reuben Shipway

Gary Rosenberg, PhD, professor in the College of Arts and Sciences and curator and Pilsbry Chair of Malacology in the Academy of Natural Sciences of Drexel University was part of a team led by Reuben Shipway, PhD, and Dan Distel, PhD, of Northeastern University, that examined and described a new anatomically and morphologically divergent species of shipworm which was published recently by The Royal Society.

“Most shipworms have adaptions for burrowing into wood, small rows of sharp teeth on the exterior shell and an organ, called a ‘caecum’, that permits them to store and digest the wood they ingest,” explained Rosenberg, who is an author on the new species and the genus. “Lithoredo abatanica is very different from all other species of shipworm – it has evolved to burrow into rock, but we don’t yet know if it is actually digesting part of the rock.”

A microscopy image of a nearly four-inch-ling Lithoredo abatanica shipworm. Credit: Marvin A. Altamina and Reuben Shipway                    

During the examination process it became clear that its wood-boring adaptations had been lost during its evolution. The caecum disappeared entirely, and the shell is much rougher, for drilling into rock.

At the other end of its body, a pair of pallets enable the animal to seal itself inside its rock burrow by blocking the siphons. The siphons, which permit water flow, are the only visible features of the animal when it’s encountered in its natural habitat—the rest is hidden away in its calcareous burrow.

The species was first found by a French Expedition in 2004. The strange freshwater habitat that the French researchers reported in the Abatan River in the Philippines spurred the current group to relocate it. “Our research group had already found the giant shipworm Kuphus in the Philippines, and named a new genus of shipworms, Tamilokus, and each had unique biological features, so we were keen to track down what proved to be another new genus, Lithoredo,” explained Rosenberg.

In August 2018, Shipway led a team that found this new species about 2 kilometers upstream from the French site after receiving a tip-off from the locals about a rock-eating clam. “It’s not surprising that the locals knew about the species,” Rosenberg said. “Since shipworms are often eaten as a delicacy in the Philippines.”

“What we didn’t expect is just how bizarre the animal turned out to be,” said Rosenberg, who finds it hard to believe that the species occurs only in that one river. “I think it will be found in other rivers on Bohol Island – but will it be found elsewhere in the Philippines, or perhaps in Indonesia? How could such an amazing animal have been overlooked for so long?”

While it’s doubtful this discovery will spur your local raw bar to start serving up shipworms on the half shell – this new discovery exemplifies the need to preserve and protect our biodiversity.

Co-authors include Marvin Altamia, Rueben Shipway and Daniel Distel of Ocean Genome Legacy Center at Northeastern University, Gary Rosenberg of Drexel University; Gisela Concepcion of the University of the Philippines; and Margo Haygood of the University of Utah.

By Emily Storz


    1. Great question. It is called a new species because this is the first time it was described in the scientific literature. That very first official description makes it a species new to science.

    2. Before our paper was published, the species didn’t have a scientific name. It’s called a new species to indicate that it received a scientific name in our paper. It already had a vernacular name “antingaw”, used by people who lived in the area of the Philippines where it was collected.

      1. I wish that information had bee included in the article. Local/indigenous knowledge is so often under appreciated or altogether ignored. It seems almost arrogant.

        1. oceanographers were visiting yap and the locals told them that octopi climbed trees at night to steal seabird eggs and were laughed at until they woke the scientists up one night and showed them

  1. Does this species burrow into and eat cement or concrete? Is there a particular type of stone or rock that it prefers, e.g. limestone?

      1. It might be able to bore in cement if the cement had a high enough limestone content. It probably couldn’t bore in concrete, because that has harder rock mixed in.

  2. Is it known how the shipworm evolved from a wood-eating mollusk to one that drills into rock? It would be amazing to find an intermediate shipworm, though I suspect the odds of finding one to be highly unlikely.
    I recall one year, on a Member’s Night, listening to Dr. Rosenberg talk about a huge shipworm on display. That was the first I had heard about this amazing animal.

    1. We don’t know exactly how the ancestors of this species made the transition to boring in rock, but I assume that it must involve a phenomenon called exaptation (formerly known as “preadaption”). The features of shipworms that let them bore in wood could also let them bore in soft rock. If there was a mutation that caused the larvae to settle on rock instead of wood, the shipworm must have been able to bore into the rock. The question would be how does it get its food, since it wouldn’t have its usual source of cellulose. The cellulose is digested by bacteria that live in the shipworm’s gills. Maybe the ancestor of Lithoredo was able to filter-feed, getting particles of food from the water, like many other bivalves. Or maybe it already had a different kind of bacteria in its gills that let it use a different food source.

  3. I found a 10 Feb.1879 article from the Gazette Courier (Massachusetts) talking about shipworms eating through marble from a shipwreck off of Long Isand.

  4. Seems unlikely Lithoredo is metabolising stone as there are no sugar molecules in it. I’m guessing it grinds into softer rock/ clay for protection and then provides a habitat for microbial prey on its gills or uses them as filters like mini baleens?
    If it was going to filter in a tunnel, it would be best to chew tunnels that align with river flow or are on projections into current. It would be interesting to know if the tunnels align with current?

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