Mysterious eggs with unknown flatworms found at record depth in Pacific
Researchers from Japanese institutions made a surprising discovery: four black eggs, containing flat worms previously unknown to science, were found in the deep heart of the Pacific Ocean. The find occurred at a depth of approximately 6,200 meters, in the abyssopelagic zone, considered one of the most inhospitable and least explored layers of the oceans.
Robotic expedition reveals secrets of the ocean abyss
The discovery is the result of robotic exploration in the abyssopelagic zone, the deepest layer of most oceans, excluding hadal trenches. Oceanographers often claim that knowledge about the ocean floor is inferior to what is known about the surface of Mars, highlighting the immense importance of each new biological revelation in this environment. The creatures that inhabit these depths still have their life cycles largely unknown.
Specimen recovery in extreme conditions
During the mission, scientists from the University of Tokyo and Hokkaido University in Japan operated a remotely operated vehicle (ROV) in the Pacific. Marine researcher Yasunori Kano from the University of Tokyo, who was controlling the ROV at the time of the discovery, chose to retrieve a sample of the eggs for detailed analysis in the laboratory. The decision was crucial, given the mysterious nature of the objects and the unusual location of the find.
More on this story: Deep-sea explorers find new species with tadpole-shaped tentacles off the coast of California
What did the mysterious eggs reveal?
Samples of the eggs were sent to a team of invertebrate biologists at Hokkaido University. Although most were damaged and empty, four remained intact. When they were examined, the team realized that they were not ordinary eggs, but rather cocoons containing small flat worms.
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Keiichi Kakui, of Hokkaido University and co-author of a 2024 study on the discovery in the journal Biology Letters, described the initial surprise. “When I saw them for the first time, as I had never seen flatworm cocoons, I thought they could be protists or something similar,” he said. “Under a stereomicroscope, I cut into one of them and a milky liquid leaked out; after blowing out the liquid with a pipette, I found white, fragile bodies in the shell and realized it was the cocoon of a flatworm.”
Identification of a new species at unprecedented depth
Subsequent DNA testing confirmed that the creatures belonged to a previously undescribed species of flatworm. This discovery sets a new depth record for free-living flatworms, surpassing previous records by a significant margin.
Check out the comparison of discovery depths:
- Current discovery:about 6,200 meters (3.85 miles)
- Previous record confirmed:approximately 5,200 meters (3.23 miles), but the specimen was attached to a piece of wood, raising doubts about its origin.
- Previous record before this:about 3,200 meters (2 miles).
Unexpected similarities to shallow-water relatives
Despite living in an extreme abyssal environment, preliminary research indicates that these deep-sea flatworms are superficially similar to their shallower water-dwelling relatives. The study published in Biology Letters points out that, although they represent the “deepest known record of free-living flatworms”, they did not show drastic developmental differences compared to those found in shallower environments. This physical similarity, despite the enormous difference in pressure, temperature and luminosity, adds a layer of complexity and interest to the study of the evolution and adaptation of marine life.
