This is a deep-sea anglerfish mating pair. These animals have rarely been observed in their natural habitat — hundreds to thousands of meters below the ocean’s surface. You’re watching one of the few known videos. And this one shows a sexually parasitic pair for the first time. That means during mating, the tiny male is attached to the female. He gets nutrients and she gets sperm. These specialized fish rarely survive the journey to the surface. Before now, most deep sea anglerfish studies used dead animals pulled up in nets and sometimes preserved in museums. In this case, the research team used a special submersible designed to capture images of creatures that live at these great depths. Like most other members of its order, this anglerfish is known for the bioluminescent, lure-like appendage that drifts in front of its mouth to attract prey. But this is the first time that what may be bioluminescence on the fish’s filaments has been documented. The swaying swarm of thin projections may act like a 3-d array of cat whiskers – sensing dangers and prey in the environment. There’s little to eat at this depth and it is very cold – leaving anglerfish with few calories to spare so it makes sense that as this video shows, the anglerfish female seems to use very little energy– slowly drifting and rolling through the water. But we don’t know much about their metabolism, the bacteria that supply their glow, or how the female’s body doesn’t reject the male’s. The special ship that took this video has been in operation since 2013 and there aren’t many like it in the world. So chances are, many anglerfish mysteries will stay that way for some time to come.