Web-Slinging Snails Discovered on Sunken Ship

Scientists worry that their presence spells trouble for threatened coral reefs

Worm Snail.jpg
Rüdiger Bieler, The Field Museum

While surveying a shipwreck in the Florida Keys, scientists found a previously unknown sea snail stuck onto the hull of the vessel. As Mary Bates reports for National Geographic, the snail is ordinary in some aspects: it has a soft body and a barbed tongue. In other ways, however, it's far from plain, sporting tentacles that sling slime. But researchers fear that it is capable of wreaking havoc on the natural coral reefs.  

The creature, first collected in 2014, belongs to a group of invertebrates known as worm snails, which have squishy bodies and long, tubular shells. Researchers have the dubbed the new snail Thylacodes vandyensis after the ship where it was found. In 2009, the USNS General Hoyt S. Vandenberg (or “Vandy,” for short) was deliberately sunk off the coast of Cape Canaveral. The ship’s new purpose would be to alleviate pressure on coral reefs by providing an alternative space for hobby divers and creating additional habitats for marine life.

The “Vandy snail” seems to have traveled long distances before hunkering down on the ship, according to a recent study published in the journal Peer J. As the authors of the study explain, morphological and DNA tests indicate that the creature may have arrived from the Pacific, where its closest cousins live. Scientists also studied museum specimens and local species to confirm that the snail was a “recent arrival” to the Florida Keys.

Scientists don’t really know how the Vandy snail traveled from foreign waters. Adult worm snails don’t move once they settle on a location, but hatchlings are mobile, Bates notes. Little Vandy snails may have hitched a ride on a ship, or simply been carried to new waters by the currents.

Researchers’ observations of the Vandy snail have revealed a host of fascinating traits and behaviors. As Mindy Weisberger explains in Live Science, the creatures have bright orange faces that peep out from openings in their shells, which can grow to about one inch long. Four tentacles sprout from the snails’ tubular bodies, and two of those tentacles are attached to mucous glands. Rather than oozing trails of slime like garden snails, however, the Vandy shoots out webs of mucous, which it uses to catch plankton and other tasty snacks. It then pulls the webs back into its mouth, filtering the food through barbs on its tongue, according to Bates.

In an interview with Nicole Mortillaro of CBC News, study co-author Timothy Rawlings opined that the Vandy snail is “kind of cute.” But the little guy’s presence may indicate trouble for already-threatened coral reefs. As Bates explains, worm snails can move in on the coral reefs, and the bioactive compounds in their slime make them an unappealing food source to fish. The creatures are also are known to host blood flukes—or parasitic flatworms—that can infect endangered loggerhead sea turtles.

With the sunken USNS Vandenberg, the snails have hit pay dirt. Because the reef system there is still forming and predators have yet to settle in, the snails have plenty of opportunity to spread—which they are doing at a rather alarming rate. According to Mortillaro, there were just three specimens attached to the shipwreck when the snails were first discovered. A year and a half later, the population had proliferated into the thousands.

In their paper, researchers note that “ongoing monitoring” of the artificial reefs will be necessary going forward, so scientists can implement effective responses to any other invasive species that might crop up in the future.

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