Distribution and morphology of the diatom genus Riaux-Gobin & Compère in Indonesian and Australian waters, including the description of sp. nov.

Samples from coastal tropical waters of Central Sulawesi, Bangka Island and Bawean Island in Indonesia and from the Great Barrier Reef at Fitzroy Island in Queensland, Australia were analysed for species composition of diatom assemblages with a focus on . Whereas samples from Fitzroy Island littoral in Australia retrieved only one species of , in Poso Bay, Indonesia, we observed at least six species. All established taxa were documented with light (LM) and scanning electron microscope (SEM) and principal component analysis (PCA) analysis was used to compare the species, based on the basic valve parameters of length, width, length to width ratio and striae density. A new species of the genus , is described from Australia. In addition, we showed the distinct nature of O.pilosellavar.rhizophorae permitting to species status. Particular attention is placed on girdle bands in this genus.