Studies on woloszynskioid dinoflagellates IV: The genus <i>Biecheleria</i> gen. nov.

<jats:title>SUMMARY</jats:title><jats:p>The well known freshwater dinoflagellate <jats:italic>Woloszynskia pseudopalustris</jats:italic> is transferred to the new genus <jats:italic>Biecheleria</jats:italic>, based on the very unusual structure of the eyespot (comprising a stack of cisternae), the apical apparatus of a single elongate amphiesma vesicle, the structure of the resting cyst, and molecular data. <jats:italic>Biecheleria</jats:italic> is phylogenetically related to <jats:italic>Symbiodinium</jats:italic> and <jats:italic>Polarella</jats:italic> of the family Suessiaceae. This family, which extends back to the Jurassic, is redefined with the eyespot (Type E <jats:italic>sensu</jats:italic> Moestrup and Daugbjerg) and apical apparatus as diagnostic features, unknown elsewhere in the dinoflagellates. <jats:italic>Biecheleria</jats:italic> also comprises the brackish water species <jats:italic>Biecheleria baltica</jats:italic> sp. nov. (presently identified as <jats:italic>Woloszynskia halophila</jats:italic>) and the marine species <jats:italic>Biecheleria natalensis</jats:italic> (syn. <jats:italic>Gymnodinium natalense</jats:italic>). <jats:italic>Gymnodinium halophilum</jats:italic> described in 1952 by B. Biecheler but apparently not subsequently refound, is transferred to <jats:italic>Biecheleria</jats:italic>. The Suessiaceae further includes the marine species <jats:italic>Protodinium simplex</jats:italic>, described by Lohmann in 1908 but shortly afterwards (1921) transferred to <jats:italic>Gymnodinium</jats:italic> by Kofoid and Swezy and subsequently known as <jats:italic>Gymnodinium simplex</jats:italic>. It only distantly related to <jats:italic>Gymnodinium</jats:italic>. A new family, the Borghiellaceae, is proposed for the sister group to the Suessiaceae, based on eyespot structure (Type B of Moestrup and Daugbjerg), the morphology of the apical apparatus (if present), and molecular data. It presently comprises the genera <jats:italic>Baldinia</jats:italic> and <jats:italic>Borghiella</jats:italic>. Cells of <jats:italic>Biecheleria pseudopalustris</jats:italic> and <jats:italic>B. baltica</jats:italic> contain a microtubular strand (msp) associated with vesicles containing opaque material. Such structures are known in other dinoflagellates to serve as a peduncle, indicating that the two species may be mixotrophic.</jats:p>