Euglena is a motile unicellular organism that possesses a single cilium. This cilium functions like a whip, allowing Euglena to move in a smooth, wave-like motion through the water.

Euglena is a versatile organism that can exist as both an autotroph and a saprotroph. As an autotroph, it is capable of carrying out photosynthesis using chloroplasts present in its cells. These chloroplasts contain the pigment chlorophyll, which allows Euglena to capture sunlight and convert it into energy-rich molecules. This makes Euglena self-sufficient, as it can produce its own food through photosynthesis.

However, in certain conditions or when light is not available, Euglena can also act as a saprotroph. As a saprotroph, it absorbs nutrients from decaying organic matter in its environment. It can engulf organic particles and break them down for digestion. This flexibility in nutritional mode allows Euglena to survive in different environments where the availability of sunlight for photosynthesis may vary.

Therefore, the correct answer is option 2, Euglena.