Euglena

Hello. I have recently started a microbio culture and today while I was checking up my euglena culture, I took a sample of the surface of the container and found numerous non-euglena nearly transparent organisms (roughly the same size although) swimming throughout. But as I took another sample of deeper water in the container, there was little or none of this unidentified organism. The organisms look like Colpidium Sp. to me but if there are any uni-cellular experts out there that can tag this organism for me that would be excellent. I have included 3 photos of the surface sample at 2 magnifications.