5 Awesome (and Occasionally Terrifying) Marine Worms

Jenny via Wikimedia Commons // CC BY 2.0

When most of us think of worms, we think of the earthworm; and though there are many species of the dirt-dwelling creatures, most look pretty similar, says Dr. Mark Siddall , Curator of the Division of Invertebrate Zoology at the American Museum of Natural History. But the marine annelids known as polychaete worms, which have bristles made of chitin, are an entirely different story. “There’s an enormous, terrifically huge diversity of those kinds of worms,” Siddall says. Here are a few superlatives from the class’s 10,000 species .

This nightmare-inducing creature’s colloquial name may have been inspired by Lorena Bobbitt, the woman who infamously cut off her husband’s penis in 1993, and it’s not hard to see why. The iridescent worm buries its body—which can grow up to 10 feet long, making it one of the longest polychaetes in the world—in the sea floor, but leaves its head, with five sensory antennae and an open set of truly terrifying jaws, exposed. There it waits patiently for prey to wander by. When that unfortunate prey gets too close, the antennae sense it, and the jaws snap closed, sometimes with enough force to slice a fish in half.

Successfully snagged prey is then dragged back into the worm’s burrow, but not much is known about what happens after that. Luis F. Carrera-Parra and Sergio I. Salazar-Vallejo, who study annelid polychaetes at Mexico’s El Colegio de la Frontera Sur, told WIRED , “We think that the eunicid injects some narcotizing or killing toxin in their prey animal, such that it can be safely ingested—especially if they are larger than the worm—and then digested through the gut.”

According to Scientific American , these guys can inflict a pretty nasty bite—but because they hang out in the ocean floor wherever it’s warm, between depths of 32 and 131 feet, you’re not likely to encounter one anytime soon. Unless, of course, you work in an aquarium. Matt Slater, curator at Newquay's Blue Reef Aquarium in Cornwall, England, said that when they discovered a 4-foot-long bobbit worm in their tank, they also discovered that the creature was “covered with thousands of bristles which are capable of inflicting a sting resulting in permanent numbness,” he told the Daily Mail .

And, while their name might suggest otherwise, females don’t slice the penises off of males. “[These worms] don’t have penises,” Siddall says. “They’re broadcast spawners,” animals that release sperms and eggs into the water at the same time, letting nature take its course from there.

Marine fishermen might not be so likely to use these annelids for bait if they knew what the worm can use to bite back: Bloodworms have a large proboscis equipped with four hollow pincers that are made out of a form of crystallized copper called atacamite. “The only other place you find [it] is in the Atacama Desert in Chile, where it’s formed by volcanoes,” Siddall says. “In order to be able to produce those fangs, it has to be able to withstand an enormous concentration of copper in its body, which can be toxic to other organisms.”

Though scientists aren’t exactly sure why the worms have copper pinchers, some, according to Siddall, believe that the copper activates the creature’s venom. “They’ve got venom glands at the base of each of these fangs and they’ll grab onto prey and envenomate it,” he says. And as you might imagine, getting bitten by a bloodworm isn’t pleasant—which Siddall knows from experience. “When the proboscis comes out, it spreads the four fangs,” he says. “When they draw the proboscis in, those four fangs close on the spot. It’s like a grappling hook. It hurts like hell.”

These 12-inch-long annelids, native to the South Pacific, use their jaws to burrow into coral. They spend their lives with their heads, called atokes, in the coral reefs, while the tail ends of their bodies, or epitokes, hang out—which might seem weird, but it’s pretty important during their annual mating season, which occurs in October or November.

Over the course of the year, the worm grows segments called epitokes, which eventually degenerate until they become, according to National Geographic , “little more than sacks engorged with either sperm or eggs,” which break off in conjunction with the phase of the full moon and spiral up to the surface. (According to the Natural History Guide to Samoa , “Each epitoke segments bear a tiny eyespot that can sense light” [ PDF ].) There, they dissolve and release their cargo in a swarming, mucousy mass. The whole process takes just a few hours, and festivals revolve around it. “People go out and gather them up in buckets and fry them up for food,” Siddall says.

What happens to the atoke section of the worm in the reef? It heals its abdomen—the process takes about a week—and then begins generating new epitokes for the next mating season.

As their name might suggest, these worms resemble multi-colored Christmas trees—but that’s not the actual worm itself. “The worms are buried in the coral,” Siddall says. “What you’re seeing is the worm’s filter feeding [and breathing] apparatus.” The apparatus is made of two spiraled plumes, complete with feather-like appendages called radioles, that span 1 to 1.5 inches [ PDF ]. In the center is a cover, or operculum; when the worm is startled, it pulls its plumes inside its tube and plugs the entrance with the operculum for protection. The worms, which live in tropical environments at depths between 10 and 100 feet, feed on phytoplankton in the water , using the hair-like cilia on the radioles to capture the animals and work them down to the worm’s mouth. One study suggests they may live for at least a decade, and potentially as long as 40 years .

Like the Palolo worm, these annelids come out in a swarm to mate in phases with the full moon. Unlike Palolo worms, they glow while they’re doing it. “After sunset on the fifth day after the fullest of the full moons, the females will come up to the surface,” Siddall says. “They’ll swim really fast in tight circles, and they’re [bioluminescing] a very bright blue. They look like little stars in the water.” This bright swarm attracts the males, who shoot up from the depths, also bioluminescing. “They come up really, really fast, like comets, jetting up to where the females are,” Siddall says. “When they get there, they dump their sperm in the water, and the females dump their eggs in the water, and that’s how they get the job done.” These worms are small: At about 1.4 inches, the females are twice as long as the males [ PDF ].

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