My PhD project focuses on the uncultivable marine protist lineage of Radiolaria. In order to elucidate their life cycle and shed light onto the long speculated reproductive radiolarian cycle, the functional profile of single-cell transcriptomes of various radiolarian life forms is investigated for sex-related essential genes. The described genes will serve as sexual cycle marker genes that will allow the estimation of radiolarian lifespan and provide a better insight into the ecological implications of each reproductive life stage. Overall, these results aim at expanding the current knowledge over the life of Rhizaria, a lineage with few cultivable representatives.