3 - Diatom, perhaps related with the genus Pleurosigma

4 - Radiolaria

5 - I think it is an hydrozoa, the dense circle in the middle would be the mouth and stomach, and I think that 3? radial canals can be seen

6 - Tintinnina

7 - Coccolitophora

8 - Stellate hair of a vascular plant

9 - Echinodermata larvae, I would go for ophiuroida or echinoida, but I can not assure it

10, 12 - Diatom

13 - Radiolaria

I recommend you any of these guides to better assure the identification:

This one for a first approach:

Larink, O., & Westheide, W. (2006). Coastal Plankton Photo Guide for European Seas, Verlag Dr. Friedrich Pfeil, Germany.

and these two for a proper id:

Conway, D. V. (2012). Marine Zooplankton of Southern Britain-Part 1: Radiolaria, Heliozoa, Foraminifera, Ciliophora, Cnidaria, Ctenophora, Platyhelminthes, Nemertea, Rotifera and Mollusca. Occasional Publication of the Marine Biological Association 25.

Trégouboff G., Rose M., 1957, Manuel De Planctonologie Méditerranéenne, Centre National de la Recherche Scientifique, 2 tomes (Textes & Illustrations), Paris.

Hi!

2a and 2b look like an harpacticoid copepod. If your sample is pelagic, I would suggest the genus Microsetella (e.g. Microsetella norvegica or M. rosea, I'm not sure which species is present in your area). The color and form of the copepod is quite recognisable (I work with this copepod a lot :D ).

2 - Probably an harpacticoid copepod, genus Microsetella

3 - Dinoflagellate, Ceratium fusus?

4 - Radiolaria

7 - Probably a foraminifer, Orbulina universa?

9 - Probably an echinoderm larva

12 - Diatom, Rhizosolenia polydactyla?