Morphology and molecular phylogeny of Gomphonemopsis sieminskae sp. nov. isolated from brackish waters of the East China Sea coast

We describe the new species Gomphonemopsis sieminskae from brackish waters of the East China Sea littoral near Ningbo, China. Two diatom strains isolated from Ulva sp. were successfully grown, then analyzed by light (LM) and scanning electron (SEM) microscopy. The new species is compared to known Gomphonemopsis species, and similarities to G. pseudoexigua and G. obscurum are emphasized. Although the size metric data overlap and the external views are fairly similar, the two taxa differ in their valve interior. Molecular barcoding strongly discriminated G. sieminskae from G. cf. exigua, while rbcL gene-based phylogeny showed G. sieminskae to be sister to Phaeodactylum tricornutum. In this respect our results confirm the recent discovery, based on molecular data, that Gomphonemopsis is a close-relative taxon to Phaeodactylum, and place it in Phaeodactylaceae instead of Rhoicospheniaceae as inferred solely from morphology.