The deep sea remains aqua incognita for the most part. Apart from a few deep sea vents and other locations of interest, the unfathomable depths of the world's oceans remain unexplored. But three expeditions to the Weddell Sea between Antarctica and the wider South Atlantic have brought to the surface more than 1,000 species, ranging from single-cell foraminifera to oddly shaped crabs.

"We have found hundreds of new marine creatures in the vast, dark, deep sea surrounding Antarctica," says Angelika Brandt, a zoologist at the University of Hamburg in Germany. "Carnivorous sponges, free-swimming worms, crustaceans and mollusks living in the Weddell Sea provide new insights into the evolution of ocean life."

The researchers extracted cores from as deep as 6,348 meters (nearly four miles), dragged sledges and nets across the seafloor and in the water column, and captured this mysterious undersea world on video.

The abundance of species sheds light on how the creatures of this dark realm evolve and spread. For example, foraminifera Epistominella vitrea found 1,000 meters (3,280 feet) deep in the Weddell Sea also thrives in the relatively shallow waters of McMurdo Sound, suggesting that it may have migrated from the shallows to the depths over time. And some of the larger creatures, such as antarcturid crustaceans, retain eyes, signifying a similar evolutionary trajectory.

Other foraminifera proved genetically identical to peers in the Arctic Ocean, suggesting a certain cosmopolitanism in these tiny creatures that have a globe-spanning range and can live in the deep sea wherever it may be found.

But most of these denizens of the deep proved unique and contradict the suggestion, based on surveys of the waters in subpolar latitudes, that biodiversity might decline in the deep polar regions. "We were absolutely surprised to find this high biodiversity," Brandt says, noting that "we do not know very much of the deep sea."