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Image credit: Jenny via Wikimedia Commons // CC BY 2.0
While earthworms might be the first thing that comes to mind when thinking of worms, marine polychaetes are a whole different world. According to Dr. Mark Siddall, Curator of the Division of Invertebrate Zoology at the American Museum of Natural History, these ocean-dwelling worms boast an astonishing variety of forms and behaviors. With over 10,000 species, polychaetes are a testament to nature’s creativity. Here are some standout examples from this diverse group.
1. The Bobbit Worm (Eunice aphroditois)
This eerie marine worm gets its name from a notorious 1993 incident involving Lorena Bobbitt, and its behavior is just as unsettling. Growing up to 10 feet long, the Bobbit Worm is one of the largest polychaetes. It hides in the ocean floor, leaving only its head with five antennae and razor-sharp jaws exposed. When prey comes near, the worm strikes with lightning speed, its powerful jaws capable of cutting a fish in two.
Once prey is captured, it is pulled into the worm’s burrow, though the details of what follows remain largely a mystery. Researchers Luis F. Carrera-Parra and Sergio I. Salazar-Vallejo, who specialize in annelid polychaetes at Mexico’s El Colegio de la Frontera Sur, explained to WIRED that they believe the worm injects a toxin to immobilize or kill its prey, allowing it to be safely consumed and digested, even if the prey is larger than the worm itself.
Scientific American notes that these worms can deliver a painful bite, but they typically reside in warm ocean floors at depths of 32 to 131 feet, making encounters rare. However, aquarium workers might not be so lucky. Matt Slater, curator at Newquay's Blue Reef Aquarium in Cornwall, England, told the Daily Mail that a 4-foot-long bobbit worm found in their tank was covered in bristles capable of causing permanent numbness if touched.
Despite their name, female bobbit worms do not sever male appendages. As Dr. Mark Siddall explains, these worms lack penises entirely. Instead, they are broadcast spawners, releasing sperm and eggs into the water simultaneously, leaving fertilization to chance.
2. Bloodworms (Genus Glycera)
Fishermen using these worms as bait might reconsider if they knew about their unique defense mechanism. Bloodworms possess a proboscis with four hollow, copper-based fangs made of atacamite, a mineral also found in Chile’s Atacama Desert. Siddall notes that producing these fangs requires the worm to tolerate extremely high levels of copper, which would be toxic to most other organisms.
While the exact purpose of the copper pincers remains unclear, some researchers, including Siddall, suggest they may activate the worm’s venom. “Each fang has venom glands at its base, allowing the worm to inject toxins into its prey,” he explains. A bite from a bloodworm is excruciating, as Siddall can attest. “The proboscis extends, spreading the four fangs, and when retracted, they clamp down like a grappling hook. The pain is intense,” he adds.
3. Palolo Worms (Palola viridis)
These 12-inch-long worms, found in the South Pacific, burrow into coral using their strong jaws. They live with their heads, or atokes, embedded in coral reefs, while their tail ends, known as epitokes, remain exposed. This unique arrangement plays a crucial role during their annual mating season in October or November.
Throughout the year, the worm develops segments called epitokes, which eventually transform into sacs filled with sperm or eggs. As National Geographic explains, these segments detach during the full moon and rise to the ocean’s surface. (The Natural History Guide to Samoa notes that each epitoke segment has a tiny eyespot sensitive to light [PDF].) Once at the surface, they dissolve, releasing their contents in a mucousy swarm. This brief event, lasting only a few hours, is celebrated with festivals. “People collect them in buckets and cook them as a delicacy,” Siddall says.
After the epitokes detach, the atoke section in the coral reef heals its abdomen within a week. It then begins regenerating new epitokes in preparation for the next mating season.
4. Christmas Tree Worms (Spirobranchus giganteus)
True to their name, these worms look like vibrant Christmas trees, though the visible part is not the worm itself. “The worms are embedded in coral,” Siddall explains. “What you see are their filter-feeding and breathing structures.” These structures consist of two spiral plumes with feathery radioles, measuring 1 to 1.5 inches [PDF]. At the center is an operculum, which acts as a protective plug when the worm retracts its plumes into its tube. Found in tropical waters at depths of 10 to 100 feet, they feed on phytoplankton using cilia on their radioles to guide food to their mouths. Studies suggest they can live up to 40 years.
5. Bermuda Glow Worm (Odontosyllis enopla)
Similar to Palolo worms, these creatures swarm to mate during full moon phases, but with a dazzling twist—they glow. “Females rise to the surface after sunset on the fifth day following the full moon,” Siddall says. “They swim rapidly in glowing blue circles, resembling tiny stars.” This display attracts males, who shoot upward like comets, also glowing. “They release sperm while females release eggs, completing the process,” Siddall adds. Females, at about 1.4 inches, are twice the size of males [PDF].
