Polarella glacialis, gen. nov., sp. nov. (Dinophyceae): Suessiaceae are still alive!

The culture CCMP 1383, obtained from sea-ice brine collected in McMurdo Sou nd (Ross Sea, Antarctica), is a small gymnodinioid dinoflagellate, This spe cies is very abundant in the upper land-fast sea ice, where it can both gro w and overwinter as a spiny encysted stage. The motile vegetative stage and the cyst produced in the culture were studied by scanning electron microsc opy (SEM) and transmission electron micrscopy (TEM), The amphiesma of the v egetative cells is constituted by thin vesicles that are organized into nin e latitudinal series of plates: three in the epitheca, two in the cingulum, and four in the hypotheca, The same tabulation is reflected in the cyst wa ll by acicular processes arising from the center of paraplates, with the ex ception of the paracingulum, in which acicular processess are absent, On th e basis of the peculiar plate pattern of this dinoflagellate, we establish the new genus Polarella and the new species Polarella glacialis (family Sue ssiaceae, order Suessiales), This species has a remarkable similarity with fossil Suessiaceae cysts dating back to the Triassic and Jurassic and repre sents, up to now, the only extant member of the subfamily Suessiaceae, Phyl ogenetic analysis based on the small-subunit ribosomal RNA gene confirmed t he placement of this species in the order Suessiales and its close relation ship with the genus Symbiodinium Freudenthal.