Carlos, I missed that when watching the video, earlier. Fascinating.
In her classic article on
Chaetospira and its cousin
Stichotricha, Joan Froud records that
Chaetospira's "anus" (more properly, cytoproct) is located on the proboscis, instead of the more typical place in the posterior of the organism. So, egestion from the front of the cell could be what we're seeing here. Of course, the amazing thing is that the critter was released alive and swam away!
In any case, the creature in your video emerges at exactly the spot where
Chaetospira keeps its "anus".
An illustration from Froud:
The "A" shows the location of the "anus," on the corkscrew proboscis of
C. muelleri. The three bumps below it are supposed to show successive stages of a pellet of digested food being ejected from the cytoproct.
http://jcs.biologists.org/content/s3-90/10/141.full.pdf
Stichotricha have forward-mounted cytoprocts, too, although they're not so far forward as this (they're rather dirty creatures, and I've watched them pile up ejected matter around their mucous tubes). If you think about it, the front is a good place for a tube-dwelling or bottle-dwelling organism to keep its anus.
