Identification of protozoa under microscope
At first glance, the organisms may hold the appearance of protozoans like ciliates. However, I am of the belief that these 'totally tubular' micro organisms are in fact diatoms. 

The diatoms are a diverse range of eucaryotic microalgae which comprise a large percentage of the phytoplankton group. (Diatomaceous earth is the residual remains of their calcareous walls)

They are likely diatoms because of their apparent hard membrane, and slight brown-green pigment, typical of heterokont diatoms.

I would be unable to specify the organism to family level. However, you may wish to complete your investigation by looking under the order 'Pennales'.

For general information regarding the Diatoms, you may visit https://en.wikipedia.org/wiki/Diatom
Morphology and description available from: https://books.google.co.uk/books?id=xhLJvNa3hw0C&amp;printsec=frontcover&amp;source=gbs_ge_summary_r&amp;cad=0#v=onepage&amp;q&amp;f=false 

Good luck