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

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