‘Unicorn of mollusks’ found in the Philippines

A giant, black, worm-like bivalve whose existence was only known from a few dead specimens and shell fragments has at long last been discovered and investigated by a team of scientists from the US and Philippines, the University of Utah announced Monday in a statement.

Known as the giant shipworm or Kuphus polythalamia, the creature is a mud-dwelling mollusk which appears to consume little food, instead choosing to gather its energy from a type of sulfur, the study authors explained in the journal Proceedings of the National Academy of Sciences.

The shipworm leaves behind three-foot-long tube-shaped shells that are “fairly common”, said lead investigator Dr. Daniel Distel, a professor, and director of the Ocean Genome Legacy Center at Northeastern University. Its shells led taxonomist Carl Linnaeus to include the creature in the book which led to the scientific naming system, Systema Naturae, the Washington Post said.

“But,” Dr. Distel added, “we have never had access to the animal living inside.” Its elusiveness led co-author and Utah microbiologist Margo Haygood to call it “the unicorn of mollusks” in an interview with the Post. Now, however, the seemingly mythical creature has been located.

Research leads to surprising findings about symbioses

Oddly enough, it was a documentary broadcast in the Philippines which ultimately led to the shipworm’s discovery. A film crew captured video of the mollusks growing, like they had been planted in a garden, in the mud of a shallow lagoon. An associate of Haygood’s stationed there learned of the report and contacted her, and she brought a team to investigate.

While at the lagoon, the study authors were able to locate a live shipworm, coax it into a PVC pipe (along with some seawater) and transport it to a laboratory for analysis. Since the creature had never been studied in depth, Haygood said, little was known about its biology, its habitat or its evolutionary history.

“We suspected the giant shipworm was radically different from other wood-eating shipworms,” she noted. “Finding the animal confirmed that.” For instance, while smaller shipworms tend to be pink, beige or white in color, the giant shipworm is “gunmetal black,” Distel told the Post. A full-grown specimen can be more than three foot long, the researchers added, and it has an odd digestive system that indicates that it does not feed using typical techniques.

While the creature has a mouth and a relatively tiny stomach, it also has extra large gills packed with bacteria. Although the researchers explained that this is not uncommon for shipworms, in most cases, these microbes help the mollusks digest wood. In the giant shipworm’s case, however, the bacteria in its gills feed off of sulfur-based compounds. Specifically, the microbes use hydrogen sulfide as energy, and in turn, produce organic carbon used by the shipworm as a food source.

The research “provides a fascinating example of symbiont displacement, phenomena we are only just beginning to observe more regularly in nature,” Nicole Dubilier, director of the Max Planck Institute for Marine Microbiology (who was not involved in the study), told the Post. “What we are now seeing is unexpected: symbioses are not as stable as we previously assumed.”


Image credit: Marvin Altamia