Morphological variability within the marine dinoflagellate Ornithocercus quadratus (Dinophysales, Dinophyceae) - evidence for three separate morphospecies

The dinoflagellate genus Ornithocercus is comprised of 15 valid morphospecies that were morphologically characterised by extraordinary winglike lists. Species determination was based mainly on the morphology of the left sulcal list, which has great variability. Whether forma delimitation of Ornithocercus quadratus was possible on the basis of infraspecific variation of the left sulcal list was the subject of this study. Additional supportive morphological features (e.g. cingular lists, cingulum, ornamentation and cell body shape) were investigated. In considering infraspecific variability, the validity of previously published forms (and varieties) of the species was reviewed and compared with our results. A total of 247 specimens of five forms of O. quadratus from the Atlantic and Pacific Oceans were examined morphologically, using light and scanning electron microscopy. The range of morphological variation of the left sulcal list (e.g. shape and rib pattern) was evaluated for each form. On the basis of this analysis, the forms O. quadratus f. simplex and O. quadratus f. intermedia have to be treated as synonyms of O. quadratus f. assimilis. The species status of O. assimilis should be reinstated, and the form O. quadratus f. schuettii is proposed to represent a separate morphospecies.