The creature in this video, taken by Eaglehawk Dive Centre in Tasmania, Australia, isn't an alien creature straight out of James Cameron's The Abyss—even if it kind of looks like it. It's a pyrosome, or an inter-connected conical colony of asexual zooids that live in warm waters.
The hundreds or thousands of tiny zooids—all of which are essentially clones, given that they reproduce asexually—share a gelatinous tissue to form a tube-like structure up to 40 feet long that glows. In fact, the name "pyrosome" means "fiery body," a reference to the blue-green bioluminescence that it emits when disturbed.
Although many times larger than a human being, the pyrosome is a slow-moving filter feeder. Each millimeter-sized zooid sucks in water, consumes the microscopic plankton in it, and ejects the waste in a tiny jet stream that, in conjunction with all the other tiny jet streams, propels the overall pyrosome at a smooth, steady pace.
[h/t IFL Science]