Hi ! I would say a nereididae. Could you get a better picture?

Also depending on the sampling location.

Cheers

Thank you very much for your answer! The sampling was done at the subtidal zone at about 10 m around the south coast of Jeju, South Korea. Unfortunately I don't have any other pictures.

Hi ! Okay no problem for the picture. The large bristles and segmentation might be identify as Amphinomidae. No more nereididae.

Have good day

Thank you for your answer! It's very helpful ^^