Nannochloropsis is a genus of alga comprising approximately 6 species. The genus in the current taxonomic classification was first termed by Hibberd (1981). The species have mostly been known from the marine environment but also occur in fresh and brackish water. All of the species are small, nonmotile spheres which do not express any distinct morphological feature, and cannot be distinguished by either light or electron microscopy. The characterisation is mostly done by rbcL gene and 18S rDNA sequence analysis. link to wiki