Massive single-celled organisms found in the Mariana Trench (via Rachel Carthy)

In one of the deepest regions of the Earth's oceans, marine biologists have discovered gigantic single-celled amoebas called xenophyophores.

During a visit to the Mariana Trench in July 2011, a team from the Scripps Institute of Oceanography sent untethered landers down into the depths of the trench, more than 10,500 metres below sea level. Each was equipped with digital video recorders and lights (because it's dark down there), protected by a thick sphere of glass.

To their surprise, they found xenophyophores, which had never before been seen below 7,500 metres. The single-celled creatures have among the largest individual cells known to mankind, with a diameter often exceeding 10 centimetres. They act as hosts for a variety of organisms, and also soak up heavy metals like lead, uranium and mercury.

The mega-cells weren't the only discoveries made by the landers. They also spotted the deepest jellyfish observed to date, which you can see gliding happily past in the video above.

Scripps' marine microbiologist, Doug Bartlett, who organised the expedition, said: "The identification of these gigantic cells in one of the deepest marine environments on the planet opens up a whole new habitat for further study of biodiversity, biotechnological potential and extreme environment adaptation."

Lisa Levin, a deep-sea biologist also from Scripps, added: "As one of very few taxa found exclusively in the deep sea, the xenophyophores are emblematic of what the deep sea offers. They are fascinating giants that are highly adapted to extreme conditions but at the same time are very fragile and poorly studied. These and many other structurally important organisms in the deep sea need our stewardship as human activities move to deeper waters."

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