The “ghost octopus” lays its eggs on the stalks of sponges anchored to metallic nodules. Scientists only discovered the pigment-free species in 2016, in the Hawaiian Archipelago at 4,290 meters below sea level. It was soon nicknamed "Casper". (NOAA) (2/12)

Species threatened by deep-sea mining: Images of some of the planet's most mysterious lifeforms.

The UN has described the deep sea as “the largest source of species and ecosystem diversity on Earth.” Life thrives particularly on the vast expanses of sea floor known as abyssal plains, amid the submarine mountains that rise from them and around superheated springs.

Extremes of temperature and pressure have proved no obstacle to the creatures here. But plans to commercially mine the seabed pose a grave threat to their survival.

Abyssal plains, the flattest places on the planet, are home to fish, eels, crustaceans, molluscs, sponges, sea cucumbers, starfish and brittle stars to name a few.

Virtually every dive to a submarine mountain, or “seamount”, reveals species endemic to that particular island of life. More than 800 species of fish have been discovered, as well as gardens of corals and sponges that attract further species of crustacean, mollusc and sea cucumber. Open-sea fauna such as tuna, sharks and sea turtles also visit, to feed on the permanent residents.

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