The vessel, though her masts be firm,
Beneath her copper bears a worm….
Far from New England’s blustering shore,
New England’s worm her hulk shall bore,
And sink her in the Indian seas,
Twine, wine, and hides, and China teas.
Selected lines from “Though All the Fates,” Henry David Thoreau
Tall-masted wooden ships of a bygone era were often plagued by shipworms, which could turn a ship’s hull into something resembling swiss cheese. Many shipwrecks were blamed on structural weakness caused by shipworms, of which there are an amazing variety of species.
Shipworms are not actually worms but long, skinny clams. It turns out that the slimy mollusks are well known among residents of the Philippines, where the elongated clams are hunted in unusual places and eaten with delight. Stories of strange freshwater shipworms in the Philippines have been tracked down by researchers, who are making new discoveries about these ancient creatures.
In a research paper published last month, an international team of scientists reported on a shipworm that eats rocks. Like the shipworms that eat wood, this newly described species uses the shell at the end of its body for burrowing. The difference is that the rock-boring clam seems to grind up and digest rocks while excreting sandy fragments.
Wood-boring shipworms have come under recent attention for their ability to digest wood with the assistance of symbiotic bacteria. Some researchers hope the bacteria will be useful in discovering new antibiotics or in the development of new sources of organic-based fuels.
What benefit the rock-boring species might be getting by eating rocks has not yet been identified. Perhaps they use the ground-up rocks to digest plankton that they suck from the water. Perhaps they are extracting some unknown nutrients from the rocks.
Photo: Dan Distel, Northeastern University
In search of the mystical rock-eating clam, the researchers traveled to the Abatan River near Bohol, Philippines, an area with mudstone cliffs, according to Reuben Shipway, lead author of the paper published in Proceedings of the Royal Society.
“We actually got a really good tip-off from one of the locals, who must have been quite bemused by what we were doing,” said Shipway, quoted in a news release by Laura Castañón of Northeastern University. “They said, ‘Look in the rocks on the bottom of the river and you’ll be able to find these animals.’”
Genetic studies of the bacteria from the rock-eating clams are underway, according to Daniel Distel of Northeastern University, another member of the research team, called Philippine Mollusk Symbiont International Collaborative Biodiversity Group.
“It’s already looking very, very interesting,” Distel told science writer Veronica Greenwood of the New York Times. “What we can say is that the bacteria we find in the gills are not related to the bacteria we’ve found in any other shipworm to date.”
The researchers have provisionally named the clam by giving it a new genus and species, Lithoredo Abatanica, although it is known to the locals as “antingaw” and is believed to help mothers with lactation.
The rock-eating clam is gathered and eaten by local residents, who typically cut it down the middle, turn it inside out and rinse it well to remove the sand, according to Kristy Hamilton, writing for IFL Science.
“It is best eaten raw dipped in a pickling sauce known as kinilaw (vinegar, onions, ginger and a bit of salt),” Warlita Manug Armildez of Bohol was quoted as saying. “It has a slippery but slightly crunchy texture, but if left in the vinegar for too long it becomes soft. It has a fishy seafood taste, a bit like sea cucumber, before dipping in the sauce.”
The taste for shipworms was credited with the discovery of another interesting species a couple years ago. Scientists knew about a giant shipworm from its pipelike skeletal remains, but they had no recent living specimens.
A television show in the Philippines, called “Kapuso Mo Jessico Soho,” featured a group of people who ate the long creature for its curative powers as well as its taste. A researcher at the University of the Philippines saw the show and reported it to others studying a variety of shipworm clams and their symbiotic bacteria.
After confirming the existence of the giant clam, the researchers traveled to the Sultan Kudarat province and met up with researchers from Sultan Kudarat State University. Leading the team was Marvin Altamia, a UP researcher affiliated with the Philippine Mollusk Symbiont International Cooperative Biodiversity Group.
They found their giant research subjects in a lagoon of rotting wood and other decaying matter. The long clams were not growing on the wood but rather were buried in the black muck, according to the account told by Jo Florendo B. Lantoc, a writer for the University of the Philippines.
“The animal easily fell into notoriety as a science fiction horror creature feature,” Lantoc wrote. “The black slimy body resembles that of a worm from hell. Its ‘head’ is all mouth with two ‘beaks’ for lips, and its tail ends with a pair of siphons and stalk-looking ‘pallets.’”
The bacteria were analyzed and found to metabolize hydrogen sulfide that was in abundance in the marsh. Somehow during evolution, the shipworms had switched from eating wood to eating nothing except for the gases emerging from the oxygen-free swamp. It developed a calcium tube for protection and oversize gills for gas absorption.
From studies of the giant shipworm, scientists were able to add to the stepping-stone theory of evolution, which describes how one symbiotic creature can quickly displace another during a forced transition to a new environment. Check out the paper in the Proceedings of the National Academy of Sciences.
Another take on the story was offered by KSL-TV in Salt Lake city.
Closer to home, another interesting story about shipworms involves a search along the West Coast to see whether invasive species, such as shipworms, may have arrived with debris from the Japanese tsunami that followed the 2011 earthquake in Japan. The story is about University of Oregon researcher Nancy Treneman, who developed special skills for finding interesting creatures among the debris that landed on the beach. Read the engaging article by Washington state writer Sarah Gilman in Hakai Magazine.
