Help IDing protozoan ciliate

[jmolaro]

I have several freshwater microcosms set up with sediment and water from a local pond for an experiment. Though I am supposed to be tracking phytoplankton changes over time, I am mostly only seeing this species, which I believe is a protozoan ciliate with a corkscrew flagellate. I've tried my best to ID it, but my experience with protozoa is limited and I haven't yet found anything that resembles this organism. Please help!

[jmolaro]

The flagellum is 15um thick and 23 um long and the diameter of the body is 35um.

[tlansing]

This is likely a contracted Vorticella. The stalk is coiled up after the peritrich has been disturbed and contracted. The chord inside the stalk is called a spasmoneme. Sometimes you will find large numbers of these ciliates attached to some substrate and watching them feed and contract is really interesting.

[Bruce Taylor]

Yes, it has a spirally-contracting stalk so it's in the family Vorticellidae. Assuming it is solitary, and not colonial, it is either Vorticella or Pseudovorticella. To identify it to genus we'd need to have a very close view of the pellicle.