An interesting group of testate amoebae is the genus Difflugia. There have been described hundreds of species, but the question is: how many of them are true species? Most descriptions are inaccurate of just based on one single test. Probably this group consists of several genera. Only DNA sequencing can help here. One of my projects is to make a visual map of all known species. It's one of the most difficult taxa to identify.

Hyalosphenia - Assulina - Arcella - Difflugia - Cyphoderia - Centropyxis - Nebela