Olifantiella Riaux-Gobin & Compère emend. Van de Vijver, 2009

Vijver, Bart Van De, Mertens, Adrienne & Dam, Herman Van, 2016, Olifantiella elisabethiana, a new raphid diatom species (Bacillariophyta) observed in the Port of Antwerp (Belgium), Phytotaxa 261 (3), pp. 251-259 : 258

Olifantiella Riaux-Gobin & Compère emend. Van de Vijver

Olifantiella taxa are small-sized symmetric Biraphidineae with: 1) parallel to slightly radiate striae, opening along their whole length on the outside (e. g. macroareolae), closed by an uninterrupted finely perforated hymen, 2) externally, a rather large hyaline, thickened zone runs all around the periphery of the valves. Internally, a hymenous velum extends from the valve mantle onto the striae in an oblique angle, forming a broad marginal canal running near the mantle from apex to apex, 3) central raphe endings bent away from the process opening, 4) raphe endings simple and very slightly bent, 5) on both valves, a process opening, unique, with different shape, width and position, 7) when observed, internal process or buciniportula, composed of more or less complex tubular structures, raised or not, ending in a bell-mouth plugged or not, or ending in a sort of fan, 8) multiple girdle bands with two to three rows of puncta occluded by a finely perforated velum; some bands lack puncta, 9) apical slits of various shape and number, internally occluded by a domed velum, 10) internally, a siliceous nodule in between the central raphe endings, 11) slightly raised helictoglossae, 12) externally an occasional small wart in the vicinity of the central nodule, and 13) a complex narrow wavy structure resembling a valvocopula (until now only observed in the generitype).

Olifantiella elisabethiana is so far the only species of this genus found in the Northern Hemisphere. All species known so far, were described from the coastal waters of tropical islands in the Indian and Pacific Ocean ( Riaux-Gobin & Compère 2009, Riaux-Gobin & Al-Handal 2012, Riaux-Gobin 2015), although based on the work of one single scientist. It is at the moment impossible to clarify the disjunct distribution of this genus. Given the typical morphology of the genus with the bucinoportula, its presence in marine and brackish samples should be noticed, even using only light microscopy techniques. Nevertheless, a literature search showed no records of the genus in for instance the Mediterranean Region nor in Western Europe. It is therefore difficult to explain the presence of Olifantiella in the Port of Antwerp. One hypothesis is that it is the consequence of an accidental introduction via the international ship transport. Large ships are known to transport reasonable amounts of viable diatoms cells in their ballast water during long trips ( Klein et al. 2010). Given the relatively large population observed at the type locality, it is clear that the presence of these valves in the harbor docks is not a coincidence and that a successful colonization took place. Klein et al. (2010) showed that several taxa, transported by long-term ship voyages, are capable of surviving in the port of arrival. Whether the populations of O. elisabethiana arrived in the Port of Antwerp in a similar way is of course at present only speculation and molecular research will be necessary to indicate the origin of the Antwerp population. Given the morphological differences with all known Olifantiella species in the tropical, a possible source population for O. elisabethiana in the tropics has still not been found.