Nannochloropsis limnetica (Eustigmatophyceae), a new species of picoplankton from freshwater

High densities of Nannochloropsis, reaching up to 5.7 X 109 cells per litre, were observed in small inland water bodies in Germany. This is one of the few evidences of a Nannochloropsis species in a freshwater habitat. We describe a new species, N. limnetica Krienitz, Hepperle, Stich and Weiler sp. nov, for which the critical taxonomic characterization is based upon 18S rRNA sequence data. The ultrastructure of this species is characterized by the absence of a plastidial girdle lamella and pyrenoids. The plastid-bounding endoplasmic reticulum is continuous with the nuclear envelope, and the protoplasm contains numerous rodlike, doubly refringent lamellate vesicles. The pigment content of N. limnetica corresponds to that of other Nannochloropsis, but echinone was also found. The fatty acid composition of N. limnetica is similar to that of marine species; however, the total amount of fatty acids (351 µg mg-1 C-1)is higher than in marine species.