engleski

˝Planktonic lifestyle lovers˝: a story of eight new marine Entomoneis species

The diatom genus Entomoneis Ehrenberg has been known as a common floristic component of marine, brackish and, to a lesser degree, freshwater habitats, with a largely unknown phylogenetic and ecological history. The genus includes diatoms with a bilobate keel elevated above the valve surface, a sigmoid canal raphe, transition between keel and valve body – so called “junction line” and numerous girdle bands. Here, we will present the recent discovery of eight morphologically diagnosable species of Entomoneis found in the marine plankton, a habitat not usually associated with a high diversity of raphid diatoms. While Entomoneis cells often occur in near–shore plankton tows, where cells from the benthos can get entrained in the water column by wave or tidal action (tychoplankton, e.g. E. alata, E. pulchra), off–shore planktonic Entomoneis are reported far less frequently, and are perhaps best known from polar habitats (E. gigantea, E. kjellmanii). Nevertheless, all known Entomoneis species were mainly described as epipelic, epiphytic or associated with sea-ice, while Entomoneis cells from deep–waters, temperate or tropical plankton until recently have been unexplored. To a degree, the poor understanding of species diversity in Entomoneis is a result of a lack of taxonomic and phylogenetic framework against which newly recorded specimens, especially from the plankton, can be compared. In 2017 we described E. tenera from the Adriatic Sea, as a first species of this genus preferring an exclusively planktonic lifestyle (Mejdandžić et al. 2017). Subsequent research revealed six additional planktonic Entomoneis species: E. pusilla, E. gracilis, E. vilicicii, E. infula, E. adriatica and E. umbratica (Mejdandžić et al. 2018). These species were characterized by unique morphological parameters such as valve shape and torsion of cells, valvocopulae shape and perforation, striae ultrastructure and density, transition between valve body and keel and specific raphe features (fibulae in raphe canal and central and terminal raphe endings). Along with morphological parameters, phylogenetic support for monophyletic and well supported species delineation based on a three-gene phylogeny contributed to new species descriptions. Additionally, we present the description of another planktonic Entomoneis from the Adriatic Sea, provisionally named E. nevidinia that is characterized by an extremely light silification of the frustules and multiple plastids within its cells. With this in mind, future research should be focused on searching the traits that are possibly shared between raphid diatom genera that prefer planktonic lifestyle as well as further in- depth investigation of Entomoneis species regarding this underappreciated species diversity combining classical morphological and phylogenetic analyses along with global metagenomics approach.

Entomoneis ; Adriatic Sea ; phytoplankton ; morphology ; phylogeny

nije evidentirano