WASHINGTON — A deep-diving robot that chiseled into the rocky Pacific seabed at a spot where two of the immense plates comprising Earth's outer shell meet has unearthed a previously unknown realm of animal life thriving underground near hydrothermal vents.

Giant tubeworms — the world's heftiest worms — and other marine invertebrates such as snails and bristle worms were found using the remotely operated underwater vehicle SuBastian. They were living inside cavities within the Earth's crust at an ocean-floor site where the Pacific is 1.56 miles (2,515 metres) deep. All the species were previously known to have lived near such vents, but never underground.

"We discovered vent animal life in the cavities of the ocean's crust. We now know that the unique hydrothermal vent ecosystem extends into the ocean's crust," said marine biologist Sabine Gollner of the Royal Netherlands Institute for Sea Research, one of the leaders of the study published this week in the journal Nature Communications.

"To our knowledge, it is the first time that animal life has been discovered in the ocean crust," Gollner added.

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