“…Richelia symbioses inside the cells of several host diatoms, such as Rhizosolenia/Guinardia and Hemiaulus, whereas Calothrix attaches epiphytically to host diatoms, such as Chaetoceros and Bacteriastrum (Gómez et al, 2005;Tuo et al, 2014Tuo et al, , 2017Venrick, 1974;Villareal, 1992). Recent studies have shown unicellular cyanobacteria and noncyanobacterial diazotrophs (particularly proteobacteria) to be more widespread and actively N 2 fixing in the marine environments than previously thought (Li et al, 2019;Moisander et al, 2010;Tang et al, 2019;Zehr et al, 2001). However, it appears that the filamentous Trichodesmium and Richelia/Calothrix remain to be crucial N 2 -fixing cyanobacteria throughout the warm oligotrophic ocean (Capone et al, 1997(Capone et al, , 2005Carpenter et al, 1999;Foster et al, 2011;Zehr, 2011).…”