What you are looking at is a female anglerfish, of a species known as the "black seadevil" for obvious reasons. It's pretty small (9 centimeters) and lives at depths of 1,900 feet and therefore has only been photographed by humans about a dozen times in history. But this one was just captured on video by researchers with the Monterey Bay Aquarium Research Institute, deep in dark depths of Monterey Canyon and not far from where they recently found the wreckage of a barge that was intentionally sunk there in 1980.
As SFGate tells us, these "black seadevils" can't see very well and they use that light-up "fishing rod" thing on their heads to attract prey. The Aquarium further explains that these rods are actually modified fin rays, and at the tip "is a small organ that contains millions of light-producing bacteria." Most male anglerfish tend to be much smaller than the females and have adapted to exist mostly as parasites living off the females, and whose sole purpose is to find and inseminate them.
Also, in re: the females, "Anglerfish can also swallow prey larger than themselves because their stomaches are highly flexible murder balloons." SFGate appears to have come up with that "murder balloons" turn of phrase, as that is not a technical term.
This image of the "black seadevil" species marks the very first time that scientists have captured one of these fish on video in its own habitat. The fish was video'd via an unmanned underwater probe from the Doc Ricketts research boat run by the MBARI.