Identification
Gram staining does not work on choanoflagellates like S. rosetta, and you can’t identify them via pathogenicity since they aren’t infectious. You could look at the DNA, but this isn’t always practical.
The best way to identify S. rosetta is to observe it under a microscope. It should look distinctly like a choanoflagellate with its collar and flagellum. Additionally, it has a slightly different shape from other species. S. rosetta is known for its rosette form, so if a sample is taken from brackish water and has choanoflagellates in this form, there is a good chance it is S. rosetta. S. rosetta is not extremely common, however.