Hi Franz,
Lovely clean photos - thanks for sharing.
I reckon it is a
Polydora sp but I am not convinced that it is
Polydora ciliata. In my memory, that species is more heavily pigmented. You might like to check it out with the ICES fiche?
http://www.ices.dk/products/fiche/Plankton/SHEET091.PDF
You are getting some great specimens and great photos - congratulations.
Boa Sorte
Brian