Deep-Sea Discovery: Mysterious Black Eggs Unveil Hidden World 4 Miles Beneath the Ocean’s Surface

Deep-Sea Discovery: Mysterious Black Eggs Unveil Hidden World 4 Miles Beneath the Ocean's Surface

Deep-Sea Discovery: Mysterious Black Eggs Unveil Hidden World 4 Miles Beneath the Ocean’s Surface

A cluster of small black eggs, spotted by a remotely operated vehicle in the depths of the Pacific Ocean, represents the first solid evidence that deep-sea flatworms inhabit depths greater than 6,000 meters (3.7 miles).

Initially, when the undersea vehicle illuminated the enigmatic black spheres, researchers at the University of Tokyo in Japan were uncertain about their nature.



Marine researcher Yasunori Kano, who operated the ROV that day, found the discovery intriguing and decided to retrieve the capsules from their resting place around 6,200 meters (20,341 feet or 3.85 miles) deep in a trench in the northwest Pacific.

Upon retrieval, Kano observed that most of the black spheres were affixed to rocks and were torn and empty. He sent four intact ones to Hokkaido University’s invertebrate biologists, Keiichi Kakui and Aoi Tsuyuki.

Upon examination, the duo found that each leathery casing, or ‘cocoon’, was approximately 3 millimeters wide and contained three to seven developing flatworms.

“When we opened the egg capsules, a milky liquid … that might have been yolk was observed along with the flatworms,” wrote Kakui and Tsuyuki in their paper.

Analyzing the DNA of the worm embryos, the duo discovered they belonged to an undescribed and unnamed species of platyhelminth, closely related to two suborders found in shallower waters.

Kakui told Rachel Funnell of IFLScience that when he received the eggs from Kano, he didn’t realize how rare they were.

The embryos appeared “indistinguishable” from shallow-water flatworms.

All flatworms are hermaphrodites, meaning they can produce both male and female gametes. Shallow water species reproduce sexually by laying eggs in leathery cocoons, which are typically attached to a substrate.

To date, scientists know very little about deep-sea, free-living flatworms, including their reproductive habits. Before this discovery, the deepest evidence of a ‘potential platyhelminth’ was found on a piece of sunken wood just over 5,200 meters deep.

Not only was this creature not confirmed as a flatworm, but it was also unclear if the wood sank with a shallow-water species or if a deep-sea flatworm found the wood after it sank.

The deepest ocean flatworm confirmed before this discovery was found at a depth of 3,232 meters.

“This study presents the deepest record for free-living flatworms and the first information on their early life stages in the abyssal zone, which were very similar to those in shallow-water forms,” concluded Kakui and Tsuyuki.

The eggs seem to have been laid by at least two adults of the same species. Given that the embryos were at different stages of development when retrieved from the deep seabed, the cocoons were likely laid over time, rather than all at once.

This suggests that shallow-water flatworms may have gradually colonized deeper habitats over time.

Source: Deep-Sea Discovery: Mysterious Black Eggs Unveil Hidden World 4 Miles Beneath the Ocean’s Surface

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