Scientists Just Found New Worm Species Living Rent-Free in a Deep-Sea ‘Glass Castle’
Deep-sea explorers found new worm species thriving inside an underwater glass sponge — and that's not all.
Picture a home so beautiful it looks like it’s made of glass—delicate, intricate, shimmering. Now imagine discovering that two brand-new species of worms have been quietly living inside one, deep on the ocean floor off the coast of Japan.
That’s exactly what a team of international scientists found during a landmark 2025 expedition, and the story of how they got there is just as fascinating as the creatures themselves.
The Nippon Foundation-Nekton Ocean Census expedition launched in June 2025, working alongside the Japan Agency for Marine-Earth Science and Technology (JAMSTEC).
Researchers boarded JAMSTEC’s vessel Yokosuka and sent a crewed submersible called the Shinkai 6500 down into two of Japan’s least-studied deep-sea regions: the Nankai Trough and the Shichiyo Seamount Chain.
What the submersible brought back was staggering: more than 528 specimens.
After the expedition wrapped, taxonomists from around the world gathered at JAMSTEC headquarters for a Species Discovery Workshop to begin the careful work of identifying and classifying everything that had been collected.
The count? 38 confirmed new species, with 28 additional candidates that may also prove to be new to science.
Two worm species and their remarkable glass home
The discovery that captured the most attention involved two new polychaete worm species found living inside a hexactinellid sponge—a deep-sea organism sometimes called a “glass sponge” or, more poetically, a “glass castle.”
These sponges build intricate, mesh-like skeletons out of silica, the same material used to make glass. The structures they create are elaborate enough to serve as shelter and habitat for other creatures.
According to the National Oceanic and Atmospheric Administration (NOAA): “Some species of glass sponges produce extremely large spicules that fuse together in beautiful patterns to form a ‘glass house’—a complex skeleton that often remains intact even after the sponge itself dies.”
“The skeleton of the glass sponge, together with various chemicals, provides defense against many predators,” the NOAA adds.
The two new worm species, named Dalhousiella yabukii and Leocratides watanabeae, have evolved to live right inside the body of the glass sponge.
A study detailing the discovery, led by Dr. Naoto Jimi, was published in the Zoological Journal of the Linnean Society on March 9.
And here’s a twist worth savoring: the host glass sponge itself may be a new, yet-to-be-named species, per the study. The worms’ home could be just as novel as the worms themselves.
A hidden world in the Nankai Trough
The second major study from the expedition zeroed in on the Nankai Trough, one of Japan’s most geologically active deep-sea regions.
Led by JAMSTEC researcher Dr. Chong Chen, the study was published in Ecosphere on Nov. 18 and represents the most comprehensive biological survey of the Nankai Trough ever undertaken.
Before this expedition, only 14 animal species were known to inhabit the area’s cold seeps—places on the ocean floor where gases and fluids leak from below the seafloor.
The new census documented 80 species. That’s a five-fold increase.
The diversity was remarkable in its breadth: 33 molluscs, 23 annelids, 11 arthropods, five ribbon worms, four echinoderms, three cnidarians, and one bryozoan—organisms spanning multiple branches of the animal kingdom, all thriving in a place most of us will never see.
The Shichiyo Seamount Chain delivered its own share of wonders. Scientists discovered coral gardens, sponge-dense habitats, and five new squat lobster species alongside those two glass-castle worms.
The findings have elevated the Shichiyo Seamount Chain’s profile in the scientific community.
It is now recognized as a region of special interest for Japanese marine science, a designation that could help guide future research and conservation priorities.
What this discovery unveils about the ocean floor
“The discoveries made in the Nankai Trough and the Shichiyo Seamount Chain remind us how little of our ocean has truly been explored,” Mitsuyuki Unno, Executive Director of The Nippon Foundation, said in a news release.
“Each new species discovery is a step toward understanding, valuing, and ultimately safeguarding our shared ocean,” he added.
With 38 confirmed new species, 28 more under review, more than 528 specimens brought back for analysis, and two peer-reviewed studies already published, the work of cataloging these findings is well underway but far from finished.
Two small worms living quietly inside a glass castle on the ocean floor remind us that even in the most inhospitable corners of the planet, life finds a way—and science is only beginning to find it.
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