Chrysolykos complanatus is a freshwater chrysophyte microalga in the genus Chrysolykos, class Chrysophyceae. The species epithet complanatus — flattened or compressed — describes a lorica that is notably flattened in lateral view compared with the more three-dimensional forms of other Chrysolykos species. This flattened lorica morphology is the primary taxonomic character distinguishing C. complanatus from the angular C. angulatus and the boot-shaped C. calceatus within the small genus Chrysolykos. The loricate chrysophytes, including Chrysolykos, are characterized by cells enclosed within a species-specific outer case from which two flagella emerge — one directed anteriorly and one often wrapped around the cell — enabling swimming in aquatic environments. C. complanatus has been recorded from Norwegian and Swedish freshwater ecosystems, contributing to the known diversity of chrysophytes in cold Scandinavian lakes and pond habitats. These boreal and subarctic freshwater environments, often characterized by low pH, low nutrient concentrations, and high dissolved organic carbon from surrounding peat bogs, support characteristic chrysophyte assemblages in which loricate forms are frequently present. The species contributes to primary production as a photoautotroph and may supplement its carbon budget through bacterivory. Chrysolykos species are minor components of most phytoplankton communities and are not known to form blooms. C. complanatus has not been evaluated under IUCN Red List criteria and is listed as Not Evaluated.