Boring worms living in shells are fascinating creatures

When marine biologists talk about boring worms, they don’t mean uninteresting fish bait. They’re referring to worms that bore into hard surfaces.

The subject came up in a recent email from Bob Leinau, a fellow marine animal fan. Bob wrote that his friend showed him a large, long-dead leopard cone snail shell that had what looked like holes an eighth-inch small in the top. Bob attached a photo, asking if I knew which predator made the holes.

I did not. I sent the photo and query to Jon-Paul Bingham, the UH cone snail researcher I visited recently. JP said, "It’s a boring worm, a bit like a feather duster worm in coral heads. Commonly seen on these bigger/older shells, it attaches itself to the shell while alive, so it’s some type of symbiotic arrangement. Enhanced mobility? As they grow they drill deeper into the shell."

Most of us think of worms as limp squishy things, so the idea of them drilling holes is hard to grasp. But the marine worms that make pits in hard surfaces don’t drill as much as chew, scour and erode. And they aren’t all worms.

Take shipworms, for instance. Those wood-munchers are clams in worm’s clothing. At the front of the clam’s long, soft body are two sharp-edged shells that grind wood into particles. The clam’s foot protrudes between the shells like a tongue, advancing the clam forward.

Like termites, bacteria in the clam’s gut digest the wood’s cellulose, the main ingredient in plant cell walls.

Another borer that really is a worm is the bone-eating snot flower, a gelatinous creature with plume-bearing gills and rootlike tendrils that penetrate the bones of dead animals. The worm does this by converting seawater to an acid that breaks down bone, allowing the worm to extract its nutrients. Again, bacteria in the gut do the digesting.

For better or worse, hundreds of species of marine worms mingle with mollusks. Some are harmless squatters but others are parasites. Because they can damage and kill oysters, clams, abalones and other shellfish, parasitic worms are of great interest in aquaculture research.

I found no studies about the specific worms that live in hollows on the shells of live cone snails, but I suspect that like most borers, the worms make their hole homes by chemical means.

The advantage of setting up housekeeping on a live cone shell may be, as JP suggested, free rides. By residing on a large carnivore, the tiny worms may also gain protection from predators. What the snail gets from the worms, no one knows.

Every time I mentioned that I was researching boring worms for this week’s column, I got snorts of laughter. Fortunately the creatures live far more interesting lives than their name implies.

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Reach Susan Scott at www.susanscott.net.