Hi, Şükrü 

I think it is testate amoebae (Testacea), may be from genus Arcella or Centropyxis??? For more accurate identification should be better photos. 

Hi. yes I agree with Ingrida - it belongs to the single-celled protists Arcellinida.

I also agree. It is a testate amoebae. I  also find this protozoa in the benthonic fauna in streams, sometimes in great number.

Yes it is one of the testate amoebae...need closer photos

Thank you very much for your comments... I have checked again and now I am sure that it is testate amoebae... 

I think it is testate amoebae

i think this is a polychete, it is benthique organism.

Yup, testate amoebae...here is a good ref. paper:

Payne et al. 2012. Testate amoebae in pollen slides. Review of Palaeobotany and Palynology v. 173, pp. 68-79.

Thank you Diana, I have noted this reference..

I think it might be a testate amoeba, possibly the genus Arcella