by Sign up for CNN’s Wonder Theory science newsletter. Explore the universe with news about fascinating discoveries, scientific advances and more.
A species of sea worm that scientists had lost sight of for nearly 70 years has finally resurfaced, thanks to some eagle-eyed sniffer dogs and a seahorse that is less than a centimeter long. When researchers analyzed images of tiny seahorses taken by divers, they found evidence of hundreds of photobombing worms living alongside the seahorses in coral colonies from Japan to Australia.
The long-lost worm is Haplosyllis anthogorgicola, a species of bristleworm or polychaete. It usually measures no more than 6 millimeters and burrows into branching gorgonian corals with a density of up to 15 worms per cubic centimeter. But the creature hasn’t been directly observed in the wild since 1956, when Kyoto University marine biologist Huzio Utinomo first identified it, scientists reported Wednesday in the journal Proceedings of the Royal Society B: Biological Sciences.
Finding these worms is extremely difficult because their small size and near-transparency make them difficult to see underwater, said study lead author Chloé Fourreau, a graduate student in the Laboratory of Molecular Invertebrate Systematics and Ecology (MISE) at the University of Ryukyu Okinawa , Japan.
“I think it’s great that this article uses crowdsourced images from the public to learn more about where and how these animals are found and what they do,” said Karen Osborn, a researcher and curator in the Department of Invertebrate Zoology at Smithsonian National Museum of Natural History in Washington, DC
With about 10,000 named species of bristleworms and perhaps twice as many yet to be discovered, there are many unanswered questions about the biology of polychaetes, interactions with other species, and “the impact they have on the areas in which they live live,” Osborn, who was not involved in the study and was not involved in the discovery, said in an email. “This article beautifully shows how they are right under our noses, but virtually unnoticed.”
Above is a close-up of a coral branch with visible burrows and protruding worms. – Chloé JL Fourreau/Proceedings of the Royal Society B
“She noticed some worms”
Study co-author Ai Takahata, a student at MISE and Forreau’s lab partner, was researching the camouflage of pygmy seahorses (Hippocampus bargibanti) when she unexpectedly found several H. anthogorgicola worms in coral samples collected in waters near Japan became.
“As she was cutting a branch of the coral, she noticed some worms coming out,” Forreau said. “She gave them to me because she knew I was interested in polychaetes, but before I looked at the worms, I didn’t even know anything about this species.”
Forreau suspected that the pygmy seahorses’ gorgonian coral colonies might produce more worms, she told CNN. In 2023, during an independent survey in southern Sukumo Bay in Kochi, Japan, she asked the boat captain to take a detour to sample corals and discovered H. anthogorgicola bristleworms in them.
But as Forreau sorted through her underwater photos of seahorses and corals, she made another unexpected discovery: the images showed the worms’ coral burrows. Maybe, she thought, this could be the case in other photos of pygmy seahorses. She and her study co-authors turned to iNaturalist, a website where people share nature images and biodiversity information, to find photos of pygmy seahorses (and possibly their worm-like neighbors).
On the branch shown here, galleries and burrows in which H. anthogorgicola worms live can be seen. – Chloé JL Fourreau/Proceedings of the Royal Society B
Because pygmy seahorses are so small – about 2.5 centimeters long – divers tend to photograph them in extreme close-ups that include detailed views of nearby corals. On iNaturalist, 489 photos of the seahorses also contained evidence of worms, the researchers reported.
Pictures of pygmy seahorses taken by divers were littered with worm photobombs. Hundreds of worms’ limbs, heads, and tails protruded from coral burrows; The scientists even counted seven examples of worms crawling on the bodies of seahorses. The worms’ tunnels snaked through coral branches and into polyps, and the researchers estimated that about 84 percent of the corals photographed were infested with worms.
Greater spread of bristleworms
Prior to this study, very little was known about the distribution range and habits of H. anthogorgicola; Summarizing the lifestyles of hard-to-find animals is particularly difficult when there is little published research on them, Forreau said.
“But our work shows that we can use the extensive information available about better-known species to learn more about less studied species like worms,” Forreau added in an email.
GPS coordinates in the iNaturalist photos extend the worms’ potential distribution much further south than previously thought, including Australia, East Timor, Indonesia, Japan, Malaysia, New Caledonia, Papua New Guinea, the Philippines and Taiwan, according to the study.
Finding H. anthogorgicola sticking out of a coral branch can be challenging because they are transparent. – Chloé JL Fourreau/Proceedings of the Royal Society B
In Utinomo’s 1956 paper, the worms were associated with just one species of coral – Anthogorgia bocki – but analysis of the photos suggests that these worms also inhabit other corals in the genus. The images also provided the first evidence that the worms interacted directly with seahorses.
Polychaetes live in a variety of habitats, “including polar ice, methane seeps and deep-sea hydrothermal vents, the spaces between corals and the vast open sea,” Osborn said. “They are crucial to food webs and provide habitat for other animals.”
The iNaturalist photos answered some long-standing questions about the lifestyle and habits of H. anthogorgicola, Forreau added.
“They confirm that the worms rely heavily on their burrows; They spend most of their time indoors,” she said. In many images, the only visible part of a worm was its antennae and other hanging limbs protruding from the tunnel. “This position suggests that worms spend a lot of time sensing their surroundings, perhaps waiting for something to eat in the water or detecting the movements of the coral polyp in order to steal its food.”
However, many of the burrows were not near polyps, suggesting the worms could be coral cleaners rather than food thieves.
“There is still a lot to learn about the relationship between the worms and the corals in which they live,” Forreau said.
Mindy Weisberger is a science writer and media producer whose work has appeared in Live Science, Scientific American, and How It Works magazines.
For more CNN news and newsletters, create an account at CNN.com
