Mystery jet-black eggs discovered in the depths of the Pacific

It’s hard to fathom how anything can survive in the deepest recesses of the world’s oceans.

The furthest down us humans have dived, without the use of a submersible, was 332.35 metres (1,090 feet), and even that relied on highly specialised equipment and an intense programme of training.

Yet, some creatures live happily thousands of feet below the wreck of the Titanic, despite the extreme pressures, limited light and bone-chilling temperatures that make up this unique environment.

Unsurprisingly, given the difficulties of exploring at such depths, we have only just begun to understand the world that exists within this abyss.

And the latest discovery has left scientists breathless with excitement.

Dr Yasunori Kano, of the University of Tokyo, was piloting a remote-operate vehicle (ROV) in the northwestern Pacific’s Kuril-Kamchatka Trench, when he spotted some jet-black eggs.

That in itself is no mean feat, given how dark it is down there, but Kano also managed to retrieve the eggs, at a depth of 6,200 metres (20,341 feet).

Unsure as to what they might be, he showed them to Dr Keiichi Kakui, of Hokkaido University, who subsequently co-authored a paper on the stunning find.

The eggs were found deep within the Kuril–Kamchatka Trench, which lies in the northwest Pacific Ocean(NOAA)

“When I first saw them [...] I thought they may be protists or something,” Kakui explained to IFLScience. (Protists are a family of typically unicellular organisms that includes most algae and some fungi.)

However, he continued: “Under a stereomicroscope, I cut one of them, and a milky liquid-like thing leaked from it.”

Kakui explained that “after blowing the milky thing with a pipette”, he found “fragile white bodies in the shell” and suddenly realised that the mysterious black balls were, in fact, the cocoons of flatworms (platyhelminths).

“At that time, I didn't know how rare this finding was, and couldn't identify what platyhelminth group they were,” he admitted.

“I was looking forward to studying them after coming back to my lab.”

Samples were then taken to Hokkaido University Museum where Kakui and his team managed to extract four intact egg capsules, finding flatworm remains inside.

One worm was treated with ethanol and dehydrated to make slides that the researchers could stain and analyse, while the DNA was extracted from the other two worms, IFL Science reports.

A marine flatworm of the procerodes littoralis species(David Fenwick/Aphotomarine)

The results revealed that their discovery was a record-breaker: these were now the deepest-dwelling free-living flatworms known on Earth.

Not only that, but their studies showed that there isn’t much difference between the development of deep-sea flatworms and their shallow-lurking cousins.

“This study provides 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,” Kakui and his co-author Aoi Tsuyuki wrote in their paper, which was published in the journal Biology Letters.

“This similarity in development between the relatively benign shallow-water and the extreme abyssal environments suggests that triclads (free-living flatworms) adapting to the latter faced primarily physiological and/or ecological adaptive challenges, rather than developmental ones.”

Kakui added that other “precious samples” had been collected for the study so there’s plenty more work left to do.

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