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, Voyage To Inner Space - Exploring the Seas With NOAA Collect
Location: Pacific Ocean, offshore Hawaii.
Credit: OAR/National Undersea Research Program (NURP)

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