It's pretty hard to see inside ciliates when they're packed full of endosymbiotic chlorellae. It would be nice to have a clearer view of the mouth, for instance...
In the absence of internal details, you might consider a free-swimming phase of Ophrydium versatile. Like this guy:
http://protist.i.hosei.ac.jp/pdb/images ... sp_02.html
....or this one:
http://www.youtube.com/watch?v=O7Bd3v_X ... re=related
Evidently, shape is quite variable, depending on what stage of development the creature is at. See:
http://www.jstor.org/stable/10.2307/3224547
In your first picture, the posterior seems to have an organelle that might be the remnants of the stalk, or holdfast, that attaches the sessile form of the ciliate to the substrate.
Size is about right. The macronucleus is said to be "band-shaped," which seems consistent with your second picture.
Apparently, there's a possible "planktonic form," which some regard as a separate free-swimming species under the name O. naumanni.
No doubt there are other possibilities (there are certainly plenty of other chlorellae-bearing ciliates, including some with truncate front ends) but this is the first one I thought of that didn't have any features that would rule it out.