This is the swima bombiviridis, a bioluminescent “Green Bomber” that was found in deep Pacific waters in 2009 by Karen Osborn of Scripps Oceanography. From ScienceMag.org

Thousands of meters below the sea, a tiny worm wriggles through the darkness, its dozens of paddle-shaped bristles moving in beautiful coordination. Suddenly, a hungry predator appears. The worm releases a glowing green sac, and the fish homes in on this bright new trophy. By the time the fish realizes the sac is no meal, the worm is long gone.

From MBARI.org.