Cyanobacteria have evolved to thrive in a diverse range of habitats, including the oceans, and exhibit stunning morphological diversity. Although Prochlorococcus is the smallest, this marine cyanobacterium is a significant contributor to global photosynthesis. Clockwise from top:  Merismopedia, Spirulina, Prochlorococcus, Anabaena. (Adpated from Ting, 2014)