I scale division = 2.5 µm.
Aspidisca are a crawling ciliate who use their clusters of hardened cilia, called cirri, to crawl over the surface of flocs, swimming and to brush bacteria (their food) off the surfaces they are travelling over.
You will see they have a little beak-like mouth that they stuff bacteria into! Aspidisca in decent numbers are a very positive sign in an activated sludge sample for two reasons.
Firstly, the presence of Aspidisca indicates that the surfaces of the flocs (aggregated bacterial biomass) are getting a good “hoovering”, exposing healthy, viable bacteria to consume the surrounding nutrients. Secondly, in my experience, when I see lots of healthy Aspidisca, the plant is usually nitrifying really well (excellent biological oxidation of ammonia).
Want to see some “live” action from Aspidisca? You’ll find a video below from Liz’s “Bug Lady” days in New Zealand.