This posting is about the first eukaryotic organism in this series, Euglena gracilis. In the following model mitochondria are given in red, photosynthetic organelles in green. Both organelles most likely are derived from formerly independent organisms via endosymbiosis. The photosynthetic organelles are thought to be derived from former eukaryotic green algae (secondary endosymbiosis).
Euglena gracilis
In the following picture the nucleus is given in purple, photosynthetic organelles in green, further organelles in brownish color and the eye spot in red.
Euglena gracilis
And here comes a model of Euglena gracilis as seen by dark field microscopy.
Euglena gracilis