Symbiomonas scintillans gen. et sp nov and Picophagus flagellatus gen. et sp nov (Heterokonta): Two new heterotrophic flagellates of picoplanktonic Size

Two new oceanic free-living heterotrophic Heterokonta species with picoplan ktonic size (< 2 mu m) are described, Symbiomonas scintillans Guillou et Ch retiennot-Dinet gen. ef sp. nov, was isolated from samples collected both i n the equatorial Pacific Ocean and the Mediterranean Sea. This new species possesses ultrastructural features of the bicosoecids, such as the absence of a helix in the flagellar transitional region (found in Cafeteria roenber gensis and in a few bicosoecids), and a flagellar root system very similar to that of C. roenbergensis, Acronema sippewissettensis, and Bicosoeca mari s. This new species is characterized by a single flagellum with mastigoneme s, the presence of endosymbiotic bacteria located close to the nucleus, the absence of a lorica and a R3 root composed of a 6+3+x microtubular structu re. Phylogenetical analyses of nuclear-encoded SSU rDNA gene sequences indi cate that this species is close to the bicosoecids C. roenbergensis and Sil uania monomastiga. Picophagus flagellatus Guillou et Chretiennot-Dinet gen. et sp. nov. was collected in the equatorial Pacific Ocean, Cells are naked and possess two flagella, This species is characterized by the lack of a t ransitional helix and lateral filaments on the flagellar tubular hairs, the absence of siliceous scales, two unequal flagella, R1 + R3 roots, and the absence of a rhizoplast. SSU rDNA analyses place this strain at the base of the Chrysophyceae/Synurophyceae lineages.