The Giant Shipworm

When it comes to mollusks, people talk a lot about the charismatic giant squids and giant clams (and for good reason!), yet, to my mind, these are not the strangest—or even the most elusive–giant mollusks. Scientists have long sought a very different creature—the giant shipworm (Kuphus polythalamia)—which they knew from its bizarre meter long tubal shell. Yet despite the fact that such shells were (relatively) plentiful—marine biologists never found a living specimen…until this spring, when internet clips revealed footage of people eating huge shipworms in the Philippines. Researchers were thus led to a remote lagoon in the archipelago where at last they discovered living giant shipworms flourishing in the foul muck. What they then discovered was the most shocking thing of all…

But first let’s provide some context. Shipworms are bivalve mollusks (like clams, oysters, and mussels) which eat wood–a surprising amount of which finds its way into the oceans. Wood is extremely difficult to digest, since it contains lignins, cellulose, and such like tough organic polymers. Shipworms digest wood the same way beavers and elephants and termites do—with help from symbiotic bacteria. This made shipworms the bane of pre-industrial mariners (who counted on intact wooden hulls in order to remain alive).

But shipworms are small, and the giant shipworm is…giant. The fact that the giant shipworm is an insane 130 cm long cylindrical clam with a gun metal blue body and obscene flesh gills which lives in a huge calcium tusk the size (and shape) of a baseball bat is not at all the strangest aspect of the creature. What is most odd about this mollusk is how it eats: it doesn’t. The foul anaerobic slime at the bottom of that lagoon in the Philippines is rich in hydrogen sulfide from decaying organic matter.

The giant shipworm doesn’t eat this decomposing matter (indeed, its mouth is all but vestigial). Instead it has bacteria in its gills which live upon hydrogen sulfide. The giant shipworm survives off of the byproducts of this bacterial respiration. It grows huge off of toxic gas. This strange metabolic cycle is of great interest to scientists for what it reveals bout symbiosis, adaptivity, and metabolism. Perhaps someday it will be useful as well. Maybe future generations of explorers will love giant shipworms for their ability to live on waste product gases just as much as vanished generations hated shipworms for eating ships.

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