High Quality Content by WIKIPEDIA articles! Synechococcus (from the Greek synechos (in succession) and the Greek kokkos (berry) is a unicellular cyanobacterium that is very widespread in the marine environment. Its size varies from 0.8 µm to 1.5 µm. The photosynthetic coccoid cells are preferentially found in well–lit surface waters where it can be very abundant (generally 1,000 to 200,000 cells per millilitre). Many freshwater species of Synechococcus have also been described.