Published in the journal International Biodeterioration & Biodegradation, the study challenges assumptions that Teredo navalis shipworms had “nearly sterile” digestive tracts. Though past research has shed light on shipworm anatomy, researchers couldn’t figure out why they are capable of breaking down wood so quickly.

To solve the mystery, researchers dissected shipworms and analyzed their stomachs and intestines, neither of which are thought to excrete enzymes capable of destroying the lignin — the substance that forms the toughest part of wood. This time they homed in on a structure other scientists had missed: the typhlosole, a sub-organ in shipworms’ intestinal wall. Past observers assumed the typhlosole helped shipworms absorb nutrients. But a closer look revealed that it played another role, hosting clusters of Alteromonas bacteria capable of producing enzymes that digest lignin.

Why bother studying shipworms and their guts?

“Not only have [shipworms] changed history, they are also ecosystem engineers and play a fundamental role in cycling carbon in aquatic environments,” Reuben Shipway, who initiated the study during postdoctoral work at the University of Massachusetts at Amherst, says in a news release. “It’s incredible that we haven’t had a full understanding of how they do this.”

Why has it taken so long to pinpoint the typhlosole and the symbiotic bacteria it hosts? “It is unknown,” the researchers write. Nor is it clear what role the bacteria play and whether such symbiotic species can be found in other types of shipworms.

Nevertheless, the analysis brings researchers closer to understanding the wood-hungry mollusks — and their potential for everything from pharmaceuticals to carbon capture — than ever before. “It’s very satisfying,” said Barry Goodell, a retired professor of microbiology of UMass Amherst who co-wrote the paper. “We’ve been trying to crack this mystery for years and we finally discovered the shipworm’s hidden bacterial symbiont secret.”