Digging 3 meters down into the dark marine mud of a former log storage pond in Mindanao, Philippines, scientists have discovered five live specimens of an elusive creature previously known only through the 1- to 1.5-meter-long calcium carbonate shells it left behind. By carefully chipping away at the end of a chalky tube (seen in photo above), researchers found a long, black, wormlike mass oozing from its casing—the first live specimen of the giant shipworm Kuphus polythalamia. The animal’s length makes it the longest of any living bivalve, a class of typically small critters including clams, oysters, and scallops. And as far as shipworms go, which usually burrow into and feed on wood from ships or sunken trees, K. polythalamia is unique for squatting down and making a home in ocean mud. A look at their digestive tracts indicates that these creatures don’t eat—or poop—a whole lot, the researchers report today in the Proceedings of the National Academy of Sciences. Wood-munching microbes on the sea floor expel hydrogen sulfide, the molecule responsible for the distinctive smell of rotting eggs. A different set of microbes living in the gills of K. polythalamia uses this hydrogen sulfide as an energy source to make carbon molecules that help sustain their shipworm host. The researchers suggest that studying the shipworms’ transition from eating wood to relying on sulfur might help illuminate the evolution of animals such as deep sea mussels and giant tube worms that consume hydrogen sulfide from hydrothermal vents on deep ocean sea floors.