I found this nice ciliate. I think it is Oxytricha chlorellichera, a name I found in a ciliate ID .pdf file.
Oxytricha chlorellichera
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janvangastel
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Bruce Taylor
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Re: Oxytricha chlorellichera
A very pretty ciliate. 
Your source probably meant to write Oxytricha chlorelligera (there is no valid ciliate species called O. chlorellichera). It is a very plausible identification, given the approximate shape of the cell and the relatively few known hypotrich species that carry symbiotic algae. Unfortunately, oxytrichids are identified by the arrangement of cirri on the ventral surface, and we don't see those. However, we do see marginal cirri encircling the cell, and enlarged frontal cirri, both of which are consistent with O. chlorelligera. Caudal cirri, if present, are short (which would rule out the similarly-shaped Caudiholosticha viridis).
So, the likelihood of O. chlorelligera is very high, but if we are being strict we should only identify this as "hypotrich with symbiotic algae," since the ventral cirri and other identifying features are concealed. There are some good reasons for holding back and not jumping at a plausible species-level identification. For one thing, if we make a habit of that, we are likely to overlook new and undescribed species when they come under observation. It is estimated that only a fraction of ciliate diversity has already been discovered and described...perhaps as little as an eighth of all species (Foissner et al., Protist Diversity and Geographical Distribution, 2009). That means that entirely new ciliates are quite likely to appear in our microscopes, if we are equipped to recognize them. If we assume that everything we see has already been described somewhere we make ourselves blind to novelty!
The true diversity of zoochlorella-bearing ciliates is likely to be even more poorly represented in the literature, because algae make it difficult to see other morphological features.
That said, if you do call it O. chlorelligera, I don't think anybody would object.
Your source probably meant to write Oxytricha chlorelligera (there is no valid ciliate species called O. chlorellichera). It is a very plausible identification, given the approximate shape of the cell and the relatively few known hypotrich species that carry symbiotic algae. Unfortunately, oxytrichids are identified by the arrangement of cirri on the ventral surface, and we don't see those. However, we do see marginal cirri encircling the cell, and enlarged frontal cirri, both of which are consistent with O. chlorelligera. Caudal cirri, if present, are short (which would rule out the similarly-shaped Caudiholosticha viridis). So, the likelihood of O. chlorelligera is very high, but if we are being strict we should only identify this as "hypotrich with symbiotic algae," since the ventral cirri and other identifying features are concealed. There are some good reasons for holding back and not jumping at a plausible species-level identification. For one thing, if we make a habit of that, we are likely to overlook new and undescribed species when they come under observation. It is estimated that only a fraction of ciliate diversity has already been discovered and described...perhaps as little as an eighth of all species (Foissner et al., Protist Diversity and Geographical Distribution, 2009). That means that entirely new ciliates are quite likely to appear in our microscopes, if we are equipped to recognize them. If we assume that everything we see has already been described somewhere we make ourselves blind to novelty!
The true diversity of zoochlorella-bearing ciliates is likely to be even more poorly represented in the literature, because algae make it difficult to see other morphological features.
That said, if you do call it O. chlorelligera, I don't think anybody would object.
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janvangastel
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Re: Oxytricha chlorelligera
Thank you Bruce. I adapted the name to 'Hypotrich with symbiotic algae, probably Oxytricha chlorelligera'.