These are scale worms - a recently discovered species that inhabits whalefalls and hydrothermal vents. While undeniably gorgeous it has also been observed that these guys will actively fight each other for resources; the arrows in the top photo indicate missing chunks of the scale plates, though damage is even more noticeable on the bottom photo. I got the pics from MBARI, check them out for more info, or @RebeccaRHelm on Twitter!