Feather duster worms, a type of annelid worm, and more specifically, tube- dwelling polychaete worms. The "arms" are actually tentacles or "radioles" at the anterior end of the worm. Most of the worms' bodies are hidden within the tubes they have constructed.
Image ID: nur01508, National Undersearch Research Program (NURP) Collection
Location: Pacific Ocean, offshore Hawaii.
Credit: OAR/National Undersea Research Program (NURP)