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Has anybody any idea what ciliate this is? It is about the same size as Paramecium and quite flexible and rotates as it swims. It was found in the sediments of a freshwater pond. It's main feature is a distinct vacuole at the anterior end (as seen in images). It's mouth is not very prominent but I think is visible in one images.

Sorry - that should be posterior end

It has a posterior vacuole, a somewhat truncate anterior, a mouth that is almost certainly apical, and a very long macronucleus (clearly visibile in the second image). So, probably a species of Prorodon, e.g. P. niveus, P. emmae, P. ellipticus. In older texts, the genus appears as Pseudoprorodon, because of a taxonomic mixup in the mid 20th century (and the species assigned to Prorodon in older sources are now mostly in Holophrya).

Hi Bruce,

Thanks for that. It sometimes seems overwhelming trying to identify these critters. Once someone points you in the right direction you can start to identify the main things to look for. I am currently using D.J. Patterson's 'Free-Living Freshwater Protozoa' for identification - which is very good. However, sometimes the key just seems to end at a dead end. Any advice from members about other sources for reference would be appreciated.