The planktonic diatoms from Xiamen Harbourare dominated by nano(<20μm)size fractions both for their species and cell number. Using TEM and SEM we found two new species: Cymatosira gibberula and Rocella marina, two genera newly recorded to China: Arcocellulus and Minutocellus, both in the
subfamily Cymatosiroideae of the family Cymatosiraceae and a new record to China: Skeletonoma menzelii.