Trachelocercid ciliates, commonly known as "swan-necked ciliates", live in marine sediment. This video shows how they make tentative movements with their knob-shaped head, and how they can contract quite quickly from time to time. Instead of swimming only with the head pointing forward, as one might expect it to, it sometimes switches direction and glides along with the "head" trailing in the back!
At one point it stops to pick around in a clump of debris. Is it picking up food particles through its "mouth" at the end of the head, or is it simply trying to find a way through the debris?
Collected from marine sediment on the coast of Denmark. Thanks to the Marine Biological Section of the University of Copenhagen for hosting our visit.