A small euglenid flagellate (this one is about 26 μm long), with a stiff “ingestion siphon” that can be protruded from the front of the cell. Sometimes, you can see this organelle moving back and forth as the creature feeds. What you can’t see in the light microscope is the tiny hatch that opens at the mouth of the feeding organelle as it slides forward.
About 58 species of Entosiphon have been named, but all of them may be considered synonymous with Entosiphon sulcatum Stein, 1878 (see Schroeck et al, 2003). Size: 26 μm
