Hi Abel,
your images are very beautiful with a high contrast and very nice balance of the bright and dark areas. Do you use a special software for image processing?
Yes, this is likely Ophryoglena! But unfortunately you didn't catch the mouth opening of the ciliate. The shape of the mouth opening is essentiell for the ID of ciliates. I've attached one of my images of Ophryoglena:
Ophyroglena show an unique shape of the mouth opening. It has the shape of a "6". To the left side of the mouth opening you can recognize the mysterious Lieberkühn body (LB) with the shape of a watch-glass. It is assumed that the Lieberkühn body is essentiell for the light sensitivity of the ciliate. Do you have any additional images of the shown specimen which shows the mouth opening. It would be helpful for an unambigious ID.
Wish you a nice evening
Martin