Tethysphytum antarcticum gen. et sp. nov. (Hapalidiales, Rhodophyta), a new non-geniculate coralline alga from Terra Nova Bay (Ross Sea, Antarctica): morpho-anatomical characterization and molecular phylogeny.

Over the last decade, our knowledge of the phylogenetic and taxonomic diversity of coralline algae has greatly progressed thanks to the use of DNA sequence data. Despite this, in some geographic regions the knowledge of coralline diversity is still incomplete, because it is entirely based on traditional morpho-anatomical grounds; Antarctica can certainly be included among these regions. During an investigation of the marine phototrophic biodiversity of the Ross Sea, a crustose coralline alga was collected from two sites in Tethys Bay. The alga formed thin crusts adherent to cobbles at ~20 m depth and showed morpho-anatomical features typical of the order Hapalidiales, family Hapalidiaceae (cell fusions, zonate tetrasporangia produced in multiporate conceptacles, and apical plugs). Molecular phylogenies based on the psbA, rbcL and 18S rRNA genes showed that this alga formed a lineage in the family Hapalidiaceae for which a formal assignment at genus level was not yet available. The only other known member of the lineage was a coralline from the Balleny Islands, named as Hapalidiaceae sp. ASG448A, for which psbA and 18S rRNA sequences were deposited in GenBank without identification at genus and species level. Based on our results, we describe this lineage as the new genus Tethysphytum Sciuto, Moschin & Moro, with the single species Tethysphytum antarcticum Sciuto, Moschin & Moro. At present, morpho-anatomical characters do not allow for the discrimination of Tethysphytum from other similar genera of Hapalidiaceae. The discovery of a new genus suggests that the diversity of coralline algae in Antarctica may have been underestimated and that molecular data will be essential for future taxonomic assessments of this group within this region.