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Canadian coastal waters of the Pacific Ocean and the Atlantic Ocean as well as inland freshwater habitats in Ontario were sampled for centrohelid heliozoans (free-living heterotrophic single-celled organisms) over a period of nearly five decades. More than 60 species and subspecies were revealed, including 1 Triangulopteris, 1 Raphidocystis, 2 Pseudoraphidocystis, 3 Raineriophrys, 4 Pseudoraphidiophrys, 12 Choanocystis, 15 Pterocystis, and 25 Acanthocystis taxa. Of these, 22 were officially named and described as new to science based primarily on the morphology of the siliceous scales that cover the cell. New species were compared with images and/or descriptions of close "relatives" to validate their new species assignments. New data on five species of Acanthocystis and one species of Choanocystis required revisions of their descriptive taxonomy that in some cases resulted in the splitting off of separate species or subspecies. Very little can be concluded about global distribution of centrohelid heliozoans, owing to the paucity of records. For many of the taxa reported here, previous records consist of just one or two findings from other parts of the world. One example is Choanocystis antarctica Tikhonenkov and Mylnikov, 2011 that was previously known only from Antarctic seawater, but is reported here from an Ontario softwater lake. [ABSTRACT FROM AUTHOR]

Red snow caused by dinoflagellates is a phenomenon rarely reported, described from the European Alps from 1914 onwards, and subsequently observed outside Europe on several occasions in Ontario, Canada. Considerable taxonomic confusion exists regarding the identity of the organism(s) causing red snow, but the most recent occurrence in 2016 in Ontario has now allowed detailed studies, including LM, SEM, TEM and molecular sequencing of the causative species. We conclude that the two species originally described as the cause of red snow, Glenodinium pascheri and Gyrodinium nivale, are synonymous and that the appropriate name for the organism is Borghiella pascheri (syn. Woloszynskia pascheri) as suggested by Moestrup & Calado in the recent volume of the Süsswasserflora. The central part of Borghiella pascheri cells is tomato red and filled with numerous organelles, whose ultrastructure indicates modified chloroplasts. Lack of cultures has prevented chemical characterization of the red pigment. Formation of temporary cysts was common in the samples. Transformation of the motile cells into temporary cysts was followed in detail, and the cysts were shown to be surrounded by the fused inner membranes of the amphiesmal vesicles, which became the cell membrane of the cysts, covered by the fused pellicle precursors. The cell membrane from the motile cell was discarded together with the outer amphiesmal vesicle membrane and the thin thecal plates, and the temporary cysts were therefore not surrounded by any pattern of vesicles. Sexual reproduction resulted in the formation of hypnozygotes. Although the species possessed several unusual features, DNA sequencing showed it to belong to Borghiella. The culture established in 1965 from the Botanical Garden in Göttingen, Germany and generally identified as Woloszynskia pascheri belongs to a separate species of Borghiella, to be described separately.The occurrence of red snow caused by dinoflagellates is discussed. [ABSTRACT FROM AUTHOR]

The life cycle of a previously undescribed chrysophyte, assigned to the new genus Rhizoochromonas, is described. It includes a small motile stage with heterokont flagellation which invades a Dinobryon lorica. Reproduction by cell division of the nearly spherical rhizopodial vegetative stage frequently leads to expulsion of the host protoplast through overcrowding of the lorica. Endogenous cysts (stomatocysts) are also formed within the Dinobryon lorica. The new family, Brehmiellaceae, is established to accommodate pseudopodial / rhizopodial chrysophytes with heterokont flagellation in the motile stage. Rhizoochromonas endoloricata gen et sp. Nov. has been found at two widely separated softwater locations in Onlario, and at one it constituted a major component of the planktonic flora during the autumns of six successive years. [ABSTRACT FROM AUTHOR]