Deep-Sea Creature Has No Place on the Tree of Life

The researchers who dropped cameras into the Japan Trench down to 9,100m last year did not find a new species. They found something considerably more unsettling: an animal that the existing framework for classifying all animal life on Earth simply cannot accommodate. Formally designated Animalia incerta sedis, meaning animal of uncertain placement, it has no phylum. Not an unconfirmed classification. Not a disputed one. None.

To appreciate why this is remarkable, a brief orientation: a phylum is not a narrow category. Arthropods are a phylum. Molluscs are a phylum. Chordates, the lineage that includes every vertebrate animal that has ever lived (including humans), are a phylum. There are approximately 35 recognized animal phyla, representing the deepest divisions in the animal kingdom below the level of kingdom itself. Researchers at the Minderoo-UWA Deep-Sea Research Centre and Tokyo University of Marine Science and Technology filmed this creature at 9,131 meters depth in the Japan Trench, looked at it carefully, consulted their colleagues, and concluded that it does not belong to any of them.

The animal is whitish, bilaterally symmetrical, with projections that initially suggested nudibranch, which is a type of sea slug, to the team. Other specialists pushed back. The appendages seemed too rigid. Others suggested "molluscan morphology" and then declined to say more, which is scientists' way of indicating that they would rather not speculate further in print. The deepest known nudibranch, for reference, was recorded at approximately 4,000 meters. This creature was filmed at more than twice that depth.

The hadal zone, 6,000 to 11,000 meters down, is the deepest and least explored part of the ocean—and it’s producing animals we can’t even classify.

Read the full story at Discover Wildlife, April 13, 2026

Hot Take: The entire discipline of taxonomy exists to answer the question "what is this thing" yet this creature's formal scientific designation is, in Latin, "we genuinely do not know." The classification system has 35 answers and this animal is none of them.