E-Microbiologist

This is Frontonia leucas (Ehrenberg, 1833) from the bottom sediment of a ditch. It can be found in plankton as well and prefers beta-mesosaprobic to alpha-mesosaprobic environments. Frontonia leucas feeds on bacteria, flagellates, diatoms, algae up to 50 μm in size, naked amoebas, testate amoebas (Arcella, Difflugia), ciliates (Coleps, Aspidisca) and even small metazoans (rotifers). The two most important characteristics for identification are the size of the oral apparatus compared to the overall size of the species and the single CV with long collecting channels.
In dirty environments (alpha-mesosaprobic) Frontonia leucas is common in sediments up to 5 cm depth.

Frontonia is a genus of free-living unicellular ciliate protists, belonging to the order Peniculida. As Peniculids, the Frontonia are closely related to members of the genus Paramecium. However, whereas Paramecia are mainly bacterivores, Frontonia are capable of ingesting large prey such as diatoms, filamentous algae, testate amoebas, and even, in some circumstances, members of their own species. In bacteria-rich saprobic conditions, Frontonia leucas can live as a facultative bacterivore.
Frontonia are widely dispersed, and members of the genus can be found in marine and freshwater environments on every continent.