Observations of two marine members of the genus Cymbellonitzschia (Bacillariophyta) from Tokyo Bay, Japan, with the description of the new species Cymbellonitzschia banzuensis

Cymbellonitzschia is a small genus of canal raphid diatoms within the Bacillariales reported from both freshwater and coastal marine environments. The genus is characterized by its distinct dorsiventral or ‘cymbelloid’ valve outline with the canal raphe either on the dorsal or, more commonly, along the ventral margin. Of the six currently described species only two freshwater representatives, the type of the name of the genus C. minima and the widely reported C. diluviana, have received detailed morphological treatments. This lack of understanding of the morphological diversity within the group hampers any efforts at understanding the relationships between species in this small but ecologically diverse genus. Presented here are observations and descriptions of two marine representatives from the genus Cymbellonitzschia, C. szulczewskii and the new species C. banzuensis sp. nov., based on light and scanning electron microscopy and a preliminary investigation of the phylogenetic position of marine Cymbellonitzschia within the Bacillariales. These species were collected co‐occurring in low tide sand samples from the Banzu Flats, Tokyo Bay, Japan. The morphology of these marine species will be compared to the documented freshwater species to better understand the morphological diversity and relationships within the genus.