Ultrastructure, pigment composition, and 18S rRNA gene sequence for Nannochloropsis granulata sp. nov. (Monodopsidaceae, Eustigmatophyceae), a marine ultraplankter isolated from the Skagerrak, northeast Atlantic Ocean

A marine ultraplankter, Nannochloropsis granulata sp. nov. (Eustigmatophyceae), was isolated from 17 m depth at a position north of Skagen, Denmark, in the Skagerrak, adjacent to the North Sea. Its ultrastructure, pigment composition, and the 18S rRNA gene sequence was studied and compared with N. oculata (Droop)Hibberd and N. salina Hibberd. The new species lacked both a pyrenoid and the lamellate vesicles present in the chloroplasts of the other two species. N. granulata had electron-dense bodies in the cytoplasm that did not resemble structures found in the other species. The red body characteristic of N. oculata was not observed in N. granulata. Remains of cell walls were conspicuous in old cultures of all three species. The pigment composition in all three species was very similar, with violaxanthin and a vaucheriaxanthin-like pigment as the dominating carotenoids. Based upon the alignment presented for the 18S rRNA gene, there were 9 nucleotide substitutions and 2 insertions/deletions between N. granulata and N. oculata, 32 substitutions and 1 insertion/deletion between N oculata and N. salina, and 32 substitutions and 4 insertions/deletions between N. granulata and N. salina. In a phylogenetic analysis the three species formed a well-supported (bootstrap value = 100)monophyletic group within the chromophyte/straminopile/heterokont assemblage.