I can't see them very well, but they look like.

I can distinguish two rotifers in the upper part of the pic; they look like Asplachna or Ascomorpha genus. 

I agree with Alfonso.  They look like rotifers to me.  Where was the sample collected?

These three objects certainly are not dinoflagellates, even size is too large for dinos. I agree with Alfonso and Ricardo, these objects look like rotifers.

Pyrocystis noctiluca