Officially, it's called the osedax, and its name, as well as its feathery appearance, make it seem like a plant from a Dr. Seuss book. But this worm also goes by fiercer monikers such as bone worm or zombie worm, and it can consume the rock-hard bones of some of Earth's biggest animals, including whales.
The zombie worm secretes acids to help it access the inner contents of those dead whale bones. Then, it uses symbiotic bacteria to convert the bone's proteins and fats into nutrients that serve as its food. Its feathery "branches" wiggle in the water, pulling in oxygen to keep the worm alive.
Female zombie worms can grow up to around 2 inches (5 centimeters) long. The males are microscopic by comparison, and females will collect a male harem of these tiny guys on their bodies. Eventually, the males find their way into the female's oviducts. The female releases her fertilized eggs into the water, the worm's lifecycle begins anew, and the zombie worms go about their business of cleaning up whale debris in the ocean's darkest corners.
Thanks to better technologies, we humans have finally begun to peer into the blackness of the Mariana Trench. Still, this underwater canyon is one of the most unexplored places on our planet, and it will likely remain so until we find new ways to peer into the depths without risking being crushed or drowned (or breaking our research budgets).
So like the trench itself, the animals that live there will continue to be mysteries, too. They may be our Earth cousins, but considering how little we know about them, they might as well be from another world.