It's not an alien, or a sea monster — it's an oarfish! Dr. Misty Paig-Tran, a marine biologist and biomechanist who focuses on filter-feeding sea creatures, is fascinated by the mysterious oarfish. She describes how this enormously long deep-ocean fish uses its dorsal fin (the fin on its back) to steady itself in the water column while it feeds on zooplankton. In this video, visit Dr. Paig-Tran in her lab as she pieces together information from 75,000 images of a 14-foot-long dead oarfish specimen. This data is used to help understand how the structure of the dorsal fin works to both move the oarfish along and keep it stationary in the water.

Most of the volcanic eruptions on planet Earth happen in the ocean! In 2009, marine scientists discovered the deepest ocean eruption ever found — the West Mata volcano in the Pacific Ocean. The kind of lava that it was spewing, called boninite lava, is some of the hottest lava on Earth — and you can see some of the explosions of molten rock in this video. Scientists compare it to a spectacular underwater fireworks display at nearly 4,000 feet deep. They also found shrimp living near the volcano's most active areas. This glimpse into undersea volcanic activity and life helps scientists understand how processes deep within Earth shape the surface and how life adapts to some of the harshest conditions on our planet.

As you descend into the ocean, you move through different environments — or zones. In the top 200 meters, sunlight is able to penetrate the water. This top layer (or zone) is called the "open ocean" or, commonly, the "photic zone." The next 800 meters is called the "twilight zone": there is very little light. When you reach 1,000 meters below the surface of the ocean, there is no light at all. You have reached the "deep ocean." The extreme pressures in this zone could crush a car, and the temperature stays near freezing.

Yet, despite these harsh conditions, there is life that survives in the deep ocean. Rich communities of microbes generate their own energy without sunlight through a process called chemosynthesis, and other animals eat them to survive. As much of the deep ocean remains unexplored, scientists have an exciting opportunity to discover and document new, unusual species that thrive under such conditions.

The seafloor is not just flat. In fact, it includes many of the landscape features that you see on land — hills, mountains, valleys — and even rivers and lakes! Underwater lakes and rivers form on the bottom of the ocean when seawater seeps up from the seafloor, dissolves the salt layer around it, and collects in the resulting depressions. Incredibly, these underwater lakes and rivers have shorelines, surfaces, and even waves! Masses of mussels line the edges of some of these lakes. The mussels have adaptations that allow them to get their nutrients from bacteria that generate energy from chemicals in the water rather than sunlight, since there isn't any. Lakes deep within the ocean — and the kinds of life that thrive there — are just a few of the fascinating features of the seafloor.

Found at an ocean depth of 1,600 feet, the anglerfish has many adaptations that help it capture a meal — a lure on its head to attract prey, flexible bones and an expandable stomach that help it swallow fish twice its size, and fins that can function as feet to walk along the seafloor.

Found at an ocean depth of 2,300 feet, this sea spider can grow larger than a tire on a car! In addition to eight long legs that carry its vital organs, the deep sea spider has extra limbs that function in cleaning, reproduction, and carrying around its young.

Found at an ocean depth of 1,800 feet, the invertebrate basket star — a tangled mass of long, twisting, turning arms — feeds mainly on zooplankton, which are microscopic animals that drift in the ocean. Tiny, sharp hooks on each arm capture prey, helping the basket star feed and survive. If one of these arms is broken off or eaten, it has the ability to regrow!

Found at an ocean depth of 6,900 feet, the deepsea lizardfish is the deepest-living super predator on Earth — eating everything that gets in its way! Razor sharp fangs and a body that includes both male and female reproductive organs are just some of the adaptations that help it survive in its deep, dark environment.

Found at an ocean depth of 4,200 feet, this eerie fish, the chimaera, has a skeleton made of cartilage and large eyes. Dots on its body act as sensory organs to detect electrical fields—helping it find prey in the dark waters of the deep sea.

Despite an environment that humans would find deadly, life thrives around hydrothermal vents on the seafloor. Hydrothermal vents are areas where mineral-rich water spews out from the seafloor. The mineral-rich water is formed by seawater seeping through Earth's crust and then being heated by magma. Microbial communities that live around the vents can convert the minerals and chemicals in the water into energy through a process called chemosynthesis. These microbes then serve as the base of a food web that supports a whole array of organisms living near the vents, far away from the reach of the Sun.

In this video, you can watch a large octopus move adeptly along the rocky ocean bottom. It uses its eight powerful tentacles to navigate rocks and crevices along the way. Observe how well the octopus—a master of disguise—blends in with its current surroundings. Octopus skin has the sophisticated ability to quickly change color patterns—an adaptation that helps the animal hide from both hungry predators and unsuspecting prey.

In the deepest, darkest depths of the ocean lives Vampyroteuthis, a bizarre member of the class of animals that includes octopuses, squids, and chambered nautiluses. Even though its name means "vampire squid," it is neither a vampire nor a squid! It is in a category all its own, with its distinctive features—large eyes, paddle-like fins, eight tentacles connected by a web, and a pair of long, thin filaments that can retract into pockets between its arms. In this video, watch as Vampyroteuthis floats gently and slowly through its dark watery environment, to which it is beautifully adapted. Vampyroteuthis expert Bruce Robison describes some of the remarkable adaptations that enable the vampire squid to eat and survive in the harsh, oxygen-depleted environment where it makes its home.