Tropical benthic diatoms are poorly known but constitute a rich resource for studies of diatom morphology and phylogeny. A remarkable tabellarioid ribbon-forming diatom with a very distinctive pattern of plastid distribution and unique valve and girdle band characters is described from Guam (Mariana Islands) as a new genus and species, Hanicella moenia. We were able to study the ultrastructure and ontogeny of the girdle bands, to compare several other genera in the Striatellales and the Rhabdonematales with numerous septate copulae and hyaline, nonseptate pleurae, and to evaluate their phylogenetic relationships. The last-formed two copulae of Microtabella interrupta have distended septa, the last interlocking with the other via a transverse ridge between two unique "ligules." The fourth pleura of Hanicella is a delicate, fimbriate band. Views of developing copulae of H. moenia indicated that the septum was formed by ingrowth from the sides rather than from the apex; this blurs the distinction between septate and scalariform valvocopulae. Phylogenetic results (i) confirmed that the Striatellales and Striatellaceae, consisting of Striatella and Pseudostriatella, are unrelated to clades containing Hyalosira, Microtabella, Hanicella, and Rhabdonema; and (ii) showed that the fRhabdonemataceae is close to, but separate from, the strongly supported Hanicella/Microtabella/Grammatophora clade, for which we propose Grammatophoraceae fam. nov. Formal genus and species descriptions of H. moenia are given and we also propose to restore Hyalosira interrupta to Microtabella with an emended genus description.
Keywords: biodiversity; coral reefs; girdle bands; phylogeny; septum ontogeny.
© 2014 Phycological Society of America.