The elusive genus Olifantiella (Bacillariophyta): South Pacific assemblage and Indo-Pacific biogeography
Résumé
The biraphid genus Olifantiella (Bacillariophyta), which was recently discovered from the Mascarene Islands (Indian Ocean), is also present in coral reef environments of the islands of Tahiti and Moorea (South Pacific) as an epiphyte on the mangrove Rhizophora stylosa. The genus Olifantiella may be considered elusive because all of its currently known species are very small and difficult to identify under a light microscope. Several Olifantiella taxa first described from Rodrigues Island are also present in the South Pacific, along with three new taxa: O. societatis sp. nov., O. sp., and O. pilosella var. rhizophorae var. nov. Olifantiella societatis resembles O. paucistriata but the buciniportula opening of the former is oblong and faces one stria only. Olifantiella societatis and O. sp. show distinctive features of the genus Olifantiella but are very rare. A description of the buciniportula in O. pilosella is given. Although it is still unclear, the role of the buciniportula may be related to the excretion of mucilaginous material. The diversity of Olifantiella taxa between the Mascarene and Society archipelagos is similar with 6–7 species, five of which are common to both. Olifantiella mascarenica and O. pilosella are the most common members of the genus in the Mascarene Islands and the South Pacific, respectively. Olifantiella has only been previously described from the Indo-Pacific Basin, but it may be a widespread tropical genus. This genus has probably been overlooked in the past or misidentified as Navicula because of its overall naviculoid shape and small size. Electron microscopy remains essential in determining the identity of very small diatoms such as Olifantiella.