An international team of marine biologists, led by researchers at Northeastern University and the University of Utah, is the first to investigate a never before studied species — the giant mud-dwelling shipworm Kuphus polythalamia. According to the researchers, this marine animal doesn’t seem to eat much; instead it gets its energy from a form of sulfur.
It is among the most infrequently observed and least understood of extant bivalves. Its enormous size (specimens may reach 5 feet, or 1.55 m, in length and 2.4 inches, or 6 cm, in diameter), unusual anatomy and habitat, set it apart from other members of Teredinidae.
Marine biologists have known about its existence for many years: long, tusk-like shells that encase the animal were first documented in the 18th century.
“But we have never had access to the animal living inside,” said Dr. Daniel Distel, director of the Ocean Genome Legacy Center at Northeastern University and lead co-author of a paper about Kuphus polythalamia in the Proceedings of the National Academy of Sciences.
Dr. Distel and his colleagues found live specimens of Kuphus polythalamia in the mud of a shallow lagoon in the Philippines.
“Five specimens of Kuphus polythalamia were collected in Mindanao, Philippines, at a depth of about 10 feet (3 m) in a marine bay formerly used as a log storage pond,” they said.
“I was awestruck when I first saw the sheer immensity of this bizarre animal,” said co-author Dr. Marvin Altamia, a researcher at the Marine Science Institute at the University of the Philippines, Quezon City, Philippines.
“Being present for the first encounter of an animal like this is the closest I will ever get to being a 19th century naturalist,” added lead co-author Prof. Margo Haygood, from the University of Utah College of Pharmacy.
Because Kuphus polythalamia had never been studied rigorously, little was known about its life history, habitat, or biology.
“We suspected the giant shipworm was radically different from other wood-eating shipworms. Finding the animal confirmed that,” Prof. Haygood said.
The normal shipworm burrows deep into the wood of trees that have washed into the ocean, munching on and digesting the wood with the help of bacteria.
Unlike its cousins, Kuphus polythalamia lives in the mud. It also turns to bacteria to obtain nourishment, but in a different way.
According to the team, Kuphus polythalamia rely on beneficial sulfur-oxidizing bacteria that live in their gills.
“Kuphus polythalamia lives in a pretty stinky place. The organic-rich mud around its habitat emits hydrogen sulfide, a gas derived from sulfur,” the researchers explained.
“Like tiny chefs, these bacteria use the hydrogen sulfide as energy to produce organic carbon that feeds the shipworm. This process is similar to the way green plants use the Sun’s energy to convert carbon dioxide in the air into simple carbon compounds during photosynthesis.”
“As a result, many of Kuphus polythalamia’s internal digestive organs have shrunk from lack of use.”
Daniel L. Distel et al. Discovery of chemoautotrophic symbiosis in the giant shipworm Kuphus polythalamia (Bivalvia: Teredinidae) extends wooden-steps theory. PNAS, published online April 17, 2018; doi: 10.1073/pnas.1620470114
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