Maybe somebody can help me for the identification. This polychaeta was 625 µm long. It did'nt have eyes. From its external form I concluded that it is a holoplanctonic (not meroplanctonic) animal.
I have no idea what this is...but I am tempted to think that it may be a reproductive stage of a syllid polychaete worm. They have a bizarre reproductive method. This blogpost gives a flavour... just the title gives a good idea of the bizarreness!