A creature filmed near the bottom of the Japan Trench at roughly 9,100 meters cannot be classified into any known animal phylum, according to a peer-reviewed study that cataloged life across three of the deepest ocean trenches on Earth. The organism, recorded twice at approximately 9,137 meters during submersible operations at the Boso Triple Junction, has been designated “Animalia incerta sedis,” a taxonomic label reserved for animals whose evolutionary relationships are completely unresolved. The finding arrived alongside dozens of other new species discoveries from the same campaign, but this particular organism stands apart because no specialist consulted could match its body plan to any described group of animals.
An unclassifiable animal at 9,137 meters in the Japan Trench
The trenches surveyed in this research span depths of 4,534 to 9,775 meters across the Japan, Ryukyu, and Izu-Ogasawara systems in the northwest Pacific Ocean. A study published in the Biodiversity Data Journal documented imagery-based identifications of fauna throughout these zones, and the organism that defied classification appeared at one of the deepest survey points. Filmed twice near 9,137 meters, its morphology did not correspond to any recognized phylum, a distinction that separates it from the usual parade of snailfish, amphipods, and sea cucumbers that dominate hadal ecosystems.
The expedition behind the discovery was a collaboration between the Nippon Foundation, Nekton’s Ocean Census program, and the Japan Agency for Marine-Earth Science and Technology (JAMSTEC), described in a campaign announcement highlighting dozens of previously unknown species from the same deep-sea survey. Separately, the 2022 DSSV Pressure Drop campaign, which involved the Minderoo-UWA Deep Sea Research Centre and Tokyo University of Marine Science and Technology, had already produced a record for the world’s deepest fish in the Japan Trench. A Nagoya University researcher set the Japanese record for the deepest manned submarine expedition during the same Ring of Fire Expedition 2022, which used the manned submersible Limiting Factor.
These overlapping campaigns built a detailed picture of what lives at extreme depth. The incerta sedis organism, however, broke the pattern. Typical hadal animals can be slotted into well-known phyla such as Arthropoda, Chordata, or Echinodermata. This creature fit none of them. Its overall form, visible in the footage, did not match the segmented limbs of arthropods, the notochords and fins of chordates, or the radial symmetry seen in most echinoderms. Specialists consulted during the study were unable to align its visible features with any existing blueprint for animal organization.
Seismic pulses and isolated hadal microhabitats
One explanation for why such a biologically orphaned organism might persist at 9,100 meters involves the tectonic character of the Japan Trench itself. A companion study in the Journal of Biogeography examined how seismic disturbance, productivity, and depth shape benthic habitats across the same trench systems. That research documented submersible dives at the Boso Triple Junction at approximately 9,137 meters and the southern Izu-Ogasawara Trench at approximately 9,775 meters, providing direct evidence that tectonic activity influences which organisms can survive at specific sites.
The Japan Trench sits along one of the most seismically active subduction zones on the planet. Earthquakes trigger turbidity currents that redistribute organic sediment, creating short-lived nutrient surges on the trench floor. These pulses could sustain organisms adapted to unpredictable food supply while simultaneously making the habitat inhospitable to species that require stable conditions. If the incerta sedis animal occupies microhabitats shaped by these disturbance cycles, it may have diverged from other lineages long ago and survived in ecological niches too volatile for more common hadal fauna. This hypothesis aligns with the companion research showing that seismic disturbance patterns correlate with distinct biological community structures at different trench sites.
The Boso Triple Junction, where three tectonic plates converge, is an especially dynamic location. Sediment flows, shifting substrates, and periodic chemical changes at the seafloor could create pockets of habitat that are geographically tiny but ecologically distinct. An animal lineage isolated in such pockets for millions of years could, in theory, diverge enough to lose recognizable affinity with any known phylum. In that scenario, the creature filmed at 9,137 meters might represent not just a new species or genus, but the surviving fragment of a much older evolutionary experiment.
No specimen, no DNA, and no phylum assignment
The most significant limitation of this discovery is that no physical specimen was recovered. The identification rests entirely on video imagery captured during lander and submersible deployments. Without tissue, researchers cannot extract DNA, run molecular phylogenetics, or compare cellular structures with known animal groups. Video alone can reveal body shape, movement patterns, and approximate size, but it cannot resolve the fine anatomical details needed to place an organism within the tree of life.
No environmental DNA sampling from the exact site where the organism was filmed has been reported in the primary dataset. The absence of genetic material means the “incerta sedis” label could persist for years unless a future expedition returns to the Boso Triple Junction with the specific goal of collecting a specimen. Even then, the extreme depth and rugged terrain make targeted sampling difficult. Landers must be robust enough to survive crushing pressure while still carrying delicate collection gear, and crewed submersibles have limited bottom time to search for a single, elusive animal.
Taxonomists have historically relied on physical specimens to describe new species and higher taxa, preserving them in museums for future study. Imagery-based identifications, like those compiled in the deep trench survey, are increasingly common in environments where sampling is logistically challenging or ethically fraught. Yet without a specimen, any claim that an organism belongs to a completely new phylum will remain provisional. The authors of the trench study acknowledge this uncertainty by using the conservative “Animalia incerta sedis” designation rather than proposing a formal name.
What an unplaced animal means for deep-sea biology
If future work confirms that the Japan Trench organism truly falls outside all known phyla, it would have far-reaching implications for how biologists understand animal evolution. The major phyla-such as mollusks, annelids, cnidarians, and arthropods-represent body plans that emerged hundreds of millions of years ago and have persisted with recognizable features ever since. A modern animal that cannot be slotted into any of these categories would suggest that additional body plans survived in hidden refuges long after they disappeared elsewhere.
Even if the creature ultimately proves to be an extreme offshoot of a known group, its existence highlights how incomplete our picture of hadal biodiversity remains. The trenches surveyed in the northwest Pacific cover vast areas, yet only narrow swaths have been imaged in detail. Each new expedition adds species to the list, from glassy sponge “castles” to translucent invertebrates, and press organizations such as PR Newswire have amplified the scale of these findings for a wider audience. Against that backdrop, one unclassifiable animal serves as a reminder that entire branches of the tree of life may still be hiding in the deepest, least accessible parts of the ocean.
For now, the 9,137-meter organism remains a tantalizing silhouette on a screen: clearly alive, clearly animal, and clearly unlike anything else yet described. Its brief appearances in the Japan Trench illustrate both the power and the limits of modern deep-sea exploration. Cameras can reach places that nets and trawls cannot, revealing forms that challenge existing categories, but only painstaking follow-up work will determine where those forms truly belong. Until a specimen is in hand, the deepest mystery of the Boso Triple Junction will continue to sit just beyond the reach of taxonomy.
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*This article was researched with the help of AI, with human editors creating the final content.
