Dive beneath the ocean's waves, past the sunlit, through the oxygen-deficient zones nearly devoid of life, down, down and down some more, to a place where the pressure would crush a human, and you will find the mysterious, alien world of the deep sea. It is 300 times the size of the space inhabited by Earth's land-dwelling species. It is unbelievably cold and cloaked in near-total darkness. Yet the blackness is alive, swarming with untold armies of fantastical creatures.
However the deep sea — roughly defined as everything below 650 feet (200 meters) — comprises a stunning 240 million cubic miles (1 billion cubic kilometers) and more than 90 percent of the living space on the planet, scientists are still trying to answer the most basic questions about it. Even though the Census of Marine Life, a decade-long international study, uncovered more than 1,200 new species (excluding microbes) in the planet's oceans, the study also highlighted just how much humans still have to learn about the deep ocean in particular.
Edith Widder, chief executive officer and senior scientist at the Ocean Research and Conservation Association said, “There must be many animals, possibly large animals, down there that we don't know about”.Over the last several decades, scientists have found some bizarre and huge creatures dwelling in the deep, such as the megamouth shark, a filter feeder that grows up to 18 feet (5 meters) long. Only dozens have ever been seen since they were discovered in the 1970s .
A Fangtooth, photographed at about 2,600 feet (800 m.) in California's Monterey Bay. This fish's fierce appearance belies its size — it's only about 5 inches (12 centimeters) long. But thanks to its huge mouth and teeth, a fangtooth can grab and eat fish and squid almost its own size.
Ctenophore is sometimes called a "sea gooseberry." Unlike medusa (what most people think of as jellyfish), ctenophores have sticky tentacles that capture small animals and particles, but do not sting their prey.
A red lobate ctenophore. Fanciful gelatinous organisms like this one are far more plentiful in the deep sea than previously suspected.