Video of the cyanobacterium Phormidium autumnale evading ingestion by Pseudomicrothorax dubius. © Agnieszka Pajdak-Stós, Institute of Environmental Sciences, Jagiellonian University, Poland, www.eko.uj.edu.pl (with permission).
P. dubius is highly specialised for feeding on filamentous cyanobacteria. Its cytopharyngeal basket is adapted for attaching to, ingesting and cutting long filaments.
Some cyanobacteria such as P. autumnale have a special mechanism of defense against ciliates, even highly specialised ones such as P. dubius.
In Phormidium, the trichome (the chain of vegetative cells) is contained within a sheath made of extracellular polysaccharide. When attacked by P. dubius, the trichome is able to withdraw inside its sheath leaving the ciliate unable to feed. Only when the filament is so short that the trichome cannot withdraw, is the ciliate able to suck it out of the sheath (Fialkowska and Pajdak-Stós, 1997).
Learn about the recent discovery of symbiotic bacteria in P. dubius.