It is likely that all living organisms can be infected by one or more viruses. One of the latest higher taxa to be converted from ‘no characterized viruses’ to ‘well characterized viruses’ are the diatoms (Bacillariophyceae, Heterokontophyta) with the recent publication of three papers characterizing an ssRNA and a ssDNA virus from two genera (Chaetoceros and Rhizosolenia) of marine planktonic diatom (Nagasaki et al., 2004, 2005; Bettarel et al., 2005). It would have been strange if viruses had not been able to exploit the dominant, in terms of global primary production, photosynthetic organisms in the ocean (assimilating perhaps as much as 20 Pg inorganic C into organic C per year), despite the less than completely convincing arguments assembled by Raven & Waite (2004) as to possible anti-viral defences unique to diatoms.