New species in the marine diatom genus Olifantiella (Bacillariophyta, Biraphidineae) from Rodrigues Island (Western Indian Ocean)

Olifantiella RIAUX-GOBIN et COMPERE (Bacillariophyta, Biraphidineae), a monospecific diatom genus from coral reef environments in Reunion Island (Western Indian Ocean), was collected from Rodrigues Island (easterly island of the Mascarene archipelago) in 2007. Several taxa with the external characteristics of Olifantiella were observed in shallow lagoon sediments. The external opening connected to the internal process is easily identified in each taxon. The processes are on the same or opposite side of the frustule, depending on the taxon. Several taxa are present: I) Olifantiella cf. mascarenica RIAUX-GOBIN et COMPERE, 2) O. rodriguensis sp. nov., with an elongate shape and a double buciniportula, 3) O. gorandiana sp. nov., with a naviculoid shape and a complex buciniportula composed of two flattened tubes, that do not protrude, flanked by two small satellites, and 4) O. pilosella sp. nov., O. paucistriata sp. nov. and O. pseudobiremis sp. nov., which are only described from external views. The scarcity and minute size of the taxa necessitated the use of scanning electron microscopy (SEM) to examine and distinguish them accurately. Some LM observations were made when possible. During previous tropical marine surveys, the genus Olifantiella may have been overlooked or misidentified, due to its small size, fragile frustules, and often naviculoid shape. We discuss the morphological diversity of the genus, e.g. the frustule and buciniportula shape and structure, and propose a formal emended description of the genus Olifantiella.