Scientists Discover Two New Worm Species Living Inside an Underwater ‘Glass Castle’
A landmark ocean expedition off Japan’s coast has confirmed 38 new species and identified 28 more candidates, including two worms found living inside the skeleton of a deep-sea glass sponge.
The Nippon Foundation-Nekton Ocean Census expedition launched in June 2025 in partnership with the Japan Agency for Marine-Earth Science and Technology (JAMSTEC).
Scientists aboard the JAMSTEC research vessel Yokosuka deployed the Shinkai 6500, a crewed submersible, to explore two understudied deep-sea regions: the Nankai Trough and the Shichiyo Seamount Chain.
The submersible brought back more than 528 specimens. After the expedition, taxonomists from around the world gathered at JAMSTEC headquarters for a Species Discovery Workshop to classify what had been found.
The final count was staggering: 38 confirmed new species, with 28 additional candidates that may also prove new to science.
New Worm Species in a ‘Glass Castle’
Among the most striking discoveries were two new polychaete worm species found living inside a hexactinellid sponge — a deep-sea organism sometimes called a “glass sponge” or a “glass castle.”
The two species, named Dalhousiella yabukii and Leocratides watanabeae, have evolved to live inside the body of the glass sponge itself.
A study detailing the discovery, led by Dr. Naoto Jimi, was published in the Zoological Journal of the Linnean Society on March 9.
Glass sponges build intricate, mesh-like skeletons out of silica — the same material used to make glass. These structures are elaborate enough to serve as shelter and habitat for other creatures.
“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,” writes the National Oceanic and Atmospheric Administration (NOAA).
“The skeleton of the glass sponge, together with various chemicals, provides defense against many predators,” the NOAA adds.
In a further twist, the host glass sponge discovered during the expedition may itself be a new, yet-to-be-named species, per the study — meaning the worms’ home could be just as novel as the worms themselves.
Biodiversity Boom in the Nankai Trough
The second major study from the expedition focused 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 the 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, a five-fold increase in known biodiversity for the region.
The species documented included 33 molluscs, 23 annelids, 11 arthropods, five ribbon worms, four echinoderms, three cnidarians, and one bryozoan — spanning multiple branches of the animal kingdom.
Surprises on the Seamount Chain
The Shichiyo Seamount Chain delivered its own revelations. Scientists discovered coral gardens, sponge-dense habitats, and five new squat lobster species alongside the two new worm species found in the glass sponge.
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.
“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.
BOTTOM LINE: With 66 potential new species from one expedition and hundreds of specimens still being analyzed, these findings underscore how much of the deep ocean remains unknown — and how much more there is left to discover.
Production of this article included the use of AI. It was reviewed and edited by a team of content specialists.
