Viruses are the most prevalent biological entities in the world’s oceans and play essential roles in its ecological and biogeochemical balance. Yet, they are the least understood elements of marine life. By unraveling the entire genome of a certain marine protist that may act as a host for many viruses, an international research team led by scientists from Stony Brook University sets the stage for future investigations of marine protist genomes, marine microbial dynamics and the evolutionary interplay between host organisms and their viruses – work that may open doors to a better understanding of the “invisible” world of marine viruses and offers a key to the ecology and health of oceans worldwide. The research is published early online in Current Biology.