Symbiomonas is a genus of eukaryotic organism notable for its unique morphology and genomic characteristics and viral associations. Symbiomonas scintillans is the only species in this genus. Initially discovered by Guillou et al. in 1999 from samples of low nutrient water in the Pacific Ocean and Mediterranean Sea, intracellular structures that resembled bacteria led to speculation that it was an endosymbiont. This heavily influenced the genus' classification and understanding, early in its discovery. Limited research on this genus allowed this information to remain uncontested for years until comprehensive genomic analysis by Cho et al. in 2024. They found no genomic evidence for endosymbiotic bacteria but rather the presence of giant viruses. Symbiomonas exhibit distinct morphological traits that allow it to live in oligotrophic marine environments where the availability of nutrients is severely limited. As some of the smallest free-living heterotrophic eukaryotes, it relies on the efficiency of their flagellar propulsion locomotion to move through the water column and capture bacterial prey. Unlike many other protists that have a protective casing structure like a lorica or shell, Symbiomonas is a naked flagellate. Along with morphological traits, these features categorize Symbiomonas as closely related to other bicosoecid heterotrophs.