The well known freshwater dinoflagellate Woloszynskia pseudopalustris is transferred to the new genus Biecheleria, 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. Biecheleria is phylogenetically related to Symbiodinium and Polarella of the family Suessiaceae. This family, which extends back to the Jurassic, is redefined with the eyespot (Type E sensu Moestrup and Daugbjerg) and apical apparatus as diagnostic features, unknown elsewhere in the dinoflagellates. Biecheleria also comprises the brackish water species Biecheleria baltica sp. nov. (presently identified as Woloszynskia halophila) and the marine species Biecheleria natalensis (syn. Gymnodinium natalense). Gymnodinium halophilum described in 1952 by B. Biecheler but apparently not subsequently refound, is transferred to Biecheleria. The Suessiaceae further includes the marine species Protodinium simplex, described by Lohmann in 1908 but shortly afterwards (1921) transferred to Gymnodinium by Kofoid and Swezy and subsequently known as Gymnodinium simplex. It only distantly related to Gymnodinium. 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 Baldinia and Borghiella. Cells of Biecheleria pseudopalustris and B. baltica 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.