Morphology of the flagellar pore complex in Prorocentrum minimum (Dinophyceae) from the Adriatic and Baltic Seas

Prorocentrum minimum (Dinophyceae), a planktonic microalga forming red tides, is considered a potentially toxic species. In view of its likely harmful role, accurate identification of P. minimum to species and/or subspecies may be particularly important. Like most thecate dinoflagellates, species identification is largely based on morphology of the theca and on features of both flagellar and auxiliary apical pores. In this study, we compared 18S rDNA gene sequences to confirm that P. minimum strains isolated from the Baltic (3 strains) and Adriatic (3 strains) Seas were the same species, and compared the morphology of the apical pore region among the strains. Our results confirm that the platelet arrangement in the apical pore region is a stable morphological character, independent of the strain origin and culture growth phase. In addition a small tooth, opposite to the apical collar in the auxiliary pore area, is proposed as an additional diagnostic character.