Researchers in Japan were able to discover mysterious black jets in the depths of the ocean.
Jet Black Eggs Found
The eggs are so shiny and smooth that they can be likened to tiny, gross marbles of darkness. The findings were detailed in the "Flatworm cocoons in the abyss: same plan under pressure" study.
The eggs, which are technically cocoons or egg capsules, were found roughly 20,000 feet deep in northwest Pacific's Kuril-Kumchatka Trench, which is one of the planet's deepest ocean trenches.
These capsules belong to flatworms, which are invertebrates with soft bodies. The discovery serves as the first clear proof that these creatures live at such extreme depths. They go beyond earlier, but uncertain, records of roughly 17,000 feet deep.
According to Keiichi Kakui, a co-author of the study from Hokkaido University, he was quite stumped by the discovery. He explains that upon seeing the eggs, he thought that they could be protists, as he has never seen cocoons of flatworms in the past.
Kakui explains that, under the lens of a stereomicroscope, he cut one of the eggs. A liquid-like and milky thing then leaked from the inside.
Flatworms in the Deep Ocean
With a remotely operated vehicle, researchers were able to find the eggs linked to two fragments of rock. While each one had a diameter of barely one inch, they had three to seven embryos of flatworms at various developmental stages.
The eggs were laid by at least two same-species adults. Considering the different developmental stages of the embryos during retrieval, the laying of the cocoons may have happened over time and not simultaneously.
DNA analysis of the two showed that they were part of a Tricladida flatworm suborder that are known to dwell in depths that are far more shallow. The researchers explained that at their phase of development, these deep-sea specimens were indistinguishable at a superficial level compared to their cousins that dwell on the surface.
As all flatworms are hermaphrodites, they are capable of producing the gametes of both males and females. Those that dwell in shallow waters sexually reproduce by laying eggs within leathery cocoons. These are typically linked to a substrate.
This means that flatworms that dwell in the deep ocean are not born to be different from those that dwell in shallow waters. The researchers conclude that this suggests that these creatures may have colonized ocean depths gradually.
Prior to this discovery, the deepest-found ocean flatworm was discovered roughly 3,232 meters deep. Not much is known about free-living flatworms in the deep sea.
The authors note that this developmental similarity between the extremely deep and relatively shallow environments suggests that the triclads that adapted to the former faced adaptive challenges that were ecological and physiological, not developmental ones.
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