The stressor-induced ecdysis takes a special place in dinoflagellate biology. During ecdysis, a cell loses the plasmalemma, outer amphiesmal vesicle membrane and, in armored species, thecal plates, becomes immotile, and then amphiesma regeneration occurs. Here we report the results of our study of cell covering rearrangement during ecdysis in the naked dinoflagellate species Amphidinium carterae Hulburt 1957. Ecdysis was induced by mechanical treatment (centrifugation). The changes in cell organization at the ultrastructural level were examined using transmission electron microscopy methods. Shedding of the plasma membrane and the outer amphiesmal vesicle membranes, fusion of the inner amphiesmal vesicle membranes were observed. The amorphous cytoplasm zone, which underlies inner amphiesmal vesicle membranes in motile cells, retains under the new plasma membrane in ecdysed cells. We showed accumulation of small vesicles and flattened tubules that apparently begin fusion to form juvenile amphiesmal vesicles in this zone. The absence of pellicle in Amphidinium dinoflagellates was suggested.

Voltage-gated potassium channels (Kv) and cyclic nucleotide-binding domain-containing cation channels HCN, CNG, and KCNH are the evolutionarily related families of ion channels in animals. Their homologues were found in several lineages of eukaryotes and prokaryotes; however, the actual phylogenetic and structural diversity of these ion channels remains unclear. In this work, we present a taxonomically broad investigation of evolutionary relationships and structural diversity of Kv, HCN, CNG, and KCNH and their homologues in eukaryotes focusing on channels from different protistan groups. We demonstrate that both groups of channels consist of a more significant number of lineages than it was shown before, and these lineages can be grouped in two clusters termed Kv-like channels and CNBD-channels. Moreover, we, for the first time, report the unusual two-repeat tandem Kv-like channels and CNBD-channels in several eukaryotic groups, i.e. dinoflagellates, oomycetes, and chlorarachniophytes. Our findings reveal still underappreciated phylogenetic and structural diversity of eukaryotic ion channel lineages.

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