Background and aims – With the advent of molecular techniques to analyze relationships among diatom genera came the realization that the complex canal raphe system has evolved in at least two separate lineages, the Bacillariales and the Rhopalodiales + Surirellales. One genus with a canal raphe system, Denticula, is a small, but morphologically diverse group of species whose systematic position has been debated since its description. Methods – Presented here is documentation of the valve and girdle band morphology of D . kuetzingii, D . tenuis, D . valida, D . rainierensis, D . vanheurckii and Epithemia zebra var. denticuloides, all freshwater taxa, based on light and scanning electron microscopy. Key results – Observations suggest that Denticula is polyphyletic, with species previously placed in Denticula allied with several different groups within the Bacillariales. Another group of species, represented here by D . vanheurckii, appears more similar morphologically to the Rhopalodiales, especially the genus Epithemia . A new genus, Tetralunata, is proposed for D . vanheurckii and its allies. This new genus is restricted to Java and Bali. Conclusion – This work emphasizes the utility of evaluating morphological features within an established phylogenetic context and is part of a larger study to investigate relationships among the Bacillariales using morphological and eventually, molecular data.

BACILLARIALES; CANAL RAPHE; DENTICULA; DIATOM; EPITHEMIA; NEW GENUS; SPECIES FLOCKS; SUMATRA; SYSTEMATICS; TETRALUNATA