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Jet Black Pearl-Like Eggs Found at the Depth of the Pacific Ocean Aren’t What You Think

Jet Black Pearl-Like Eggs Found at the Depth of the Pacific Ocean Aren’t What You Think

Freshly collected egg capsules (or cocoons) and flatworms. Photo: Biology Letters/Royal Society Publishing

The deepest reaches of the ocean are a realm still comparatively unknown to man. These dark reaches constitute some of the most mysterious areas of the world; we even know more about outer space than we do about the deep dark belly of our planet’s oceans.

But the human thirst for discovery is also great. Where the ocean determinedly hides its secrets in its dark bosom, we doggedly probe more and more of its wondrous secrets.

The majority of these discoveries come in the form of new flora and fauna. The sheer volume of the world’s oceans hides so many diverse species that we always seem to be discovering new ones – and yet only seem to have only scratched the proverbial surface.

A dark, pearly surprise

Thanks to pop culture, we both abhor and are intrigued by mysterious eggs. The much unknown nature of what beings may emerge from such unknown capsules is enough to stir up our imagination. Now imagine finding jet black eggs deep in the Pacific Ocean while piloting a Remote Operating Vehicle, or an ROV, 6,000 metres deep, inside what is called the abyssal zone. That’s what happened to Dr Yasunori Kano, a biologist and associate professor at the University of Tokyo, while he was studying the Kuril-Kamchatka Trench in an ROV called the Hakuho-Maru.

Credit: KAlder10, CC BY-SA 4.0

Kano came across these black pearl-like eggs at a depth of 6,200 meters (or 20,300 feet). He was not sure of the nature of these black eggs, so he took them to Dr Keichi Kakui of Hokkaido University, who is a systemic zoologist dealing with the biology of marine invertebrates, to have a look.

Kakui cut one of the eggs open to find a milky fluid like substance, which on closer inspection revealed fragile white bodies under a stereomicroscope. That is when Kakui realised that these “eggs” were actually cocoons of platyhelminthes, commonly known as flatworms.


Flatworms are a group of about 22,500 species of invertebrates that are found on land and in water. They are considered to be a stepping stone in the evolution of bilaterally symmetrical life forms. About 75% of flatworm species are parasitic, the most well-known being the infamous tapeworms. However many flatworms are predators and prefer to hunt their prey on forest floor litter and fresh and salt water bodies.

Photo: Eychenne/Pixabay

Ocean-dwelling flatworms are often stunning and beautiful creatures that, sadly, many buy to adorn their aquariums. The thing is, these saltwater invertebrates have only ever been found in shallow waters, among coral reefs and such.

This discovery, and Kakui’s study, published in Biology Letters, places these flatworms at their deepest yet known depth. That is a monumental discovery, showing us how much there is to truly learn about the mystical ocean depths. Let’s try to protect those depths before we lose what we don’t even know exists.

Dr Rohan Manna is a dentist.

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