(A) 18S rRNA gene copy number per cell belonging to the major single celled eukaryotic plankton groups: Bacillariophyta (Stramenopiles), Dinoflagellata (Alveolata), Ciliophora (Alveolata) and flagellated cells. See Supplementary Table 1 for the median, mean and standard deviation values. (B) Log-log correlation between the number of 18S rRNA copies and cellular C-content (pgC cell-1). The linear regressions were significant (p < 0.05) for all groups. Data were obtained through different methodological approaches: qPCR (Zhu et al. 2005), real-time PCR (Godhe et al. 2008), single-celled qPCR (Gong et al. 2013), bioinformatics pipeline (Gong, Marchetti 2019) and single cell digital PCR (Yarimizu et al. 2021).