SUMMARY A dinophyte strain, WY98, was established by incubating an ellipsoid cyst from recent sediments collected in a freshwater reservoir in Fuzhou, China. Cell morphology and life cycle were examined using light and scanning electron microscopy. Motile cells of strain WY98 have an archetypical plate pattern similar to that of Peridinialean/Gonyaulacalean, exhibiting a plate pattern of 4′, 4a, 7′′, Z, 4s, 6′′′, and 2′′′′. This strain is characteristic in having a horseshoe‐shaped eyespot, a smooth thecal surface, and two antapical plates of unequal size. This strain is described as Sphaerodinium shuikouense sp. nov. Sphaerodinium shuikouense showed a diurnal migration and turned motile in a light period and immotile in a dark period. Asexual reproduction begins during the immotile stage, but the division is completed during the motile stage. Molecular phylogenetics using concatenated ribosomal RNA gene sequence data identified Sphaerodiniaceae as a member of the Suessiales and Sphaerodinium shuikouense as a relative of S. cracoviense and one Cystodinium species. The relatively high number of thecal plates suggests that Sphaerodinium occupies an intermediate phylogenetic position between suessioid and peridinioid dinophytes.
Zhao et al. (Fri,) studied this question.